From nek5000-users at lists.mcs.anl.gov Fri Sep 2 03:40:58 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 2 Sep 2016 08:40:58 +0000 Subject: [Nek5000-users] Suggestion about choice of Example Message-ID: Hello Neks, I am looking for some suggestions about the choice of example for my model. I want to study the flow around a 3-D bluff body in a wind tunnel set-up to calculate its drag and yawing moment (only velocity field no heat transfer/) so as to compare it with my previous study in which I used RANS SST model in CFX. Being quite new with the NEK code I need some help and useful suggestions. Thanks in advance. Shivang Aggarwal From nek5000-users at lists.mcs.anl.gov Fri Sep 2 10:03:59 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 2 Sep 2016 17:03:59 +0200 (CEST) Subject: [Nek5000-users] problem with pressure calculation Message-ID: Hi Neks, I'm having a problem with the computation of my pressure. I am simulating a flow past an airfoil. I'm using user defined velocity bounday condition at the inlet (set as 'v'), and zero gradient at the outlet. I implemented a von Karman isotropic turbulence model at the inlet of my domain, on which I impose in the userbc U+u', v' and w'(flow in x direction). The model gives correct description of the perturbation , spatially and in time. With constant velocity the problem works fine, but when I add the fluctuation, the local pressure becomes randomed and jump from a value to another with no correlation at all. The velocities look just fine in all cases. I tried to use call dsavg(u) to ensure I am C0-continuous, but it didn't work i.e. I guess I am already, and since I use only one random number to generate my von Karman spectra, there is no reason not to be, at least spatially. I have more doubts about my time correlation, where I use a basic asymmetric time filter that seems to induce quite random behavior near low amplitudes fluctuations. Some time ago, I also had the same problem by setting a random noise at the inlet. I also tried to tighten the convergence by decreasing p21(10e-8,10e-9, 10e-10..) in the rea but it have no effect at all. I also checked my model with flow past a flat plate and it gives similar problem. after calling the subroutine in usechk, I just add the fluctuation writing ux=U+utm(ix,iy,iz,e), uy= .... in userbc Any comments will be very much appreciated and thank you in advance. Antoine PS: Below is my parameters in the rea file, and a part of the userbc in case there is something I missed... ****** PARAMETERS ***** 2.6099999 NEKTON VERSION 3 DIMENSIONAL RUN 118 PARAMETERS FOLLOW 1.0000 p001 DENSITY 0.000001 p002 VISCOS 0.00000 p003 0.00000 p004 0.00000 p005 0.00000 p006 1.00000 p007 RHOCP 1.00000 p008 CONDUCT 0.00000 p009 000000.00000 p010 FINTIME 0100.000 p011 NSTEPS 2500.00000 p012 DT 0.00000 p013 IOCOMM 00000.00000 p014 IOTIME 00000025.00 p015 IOSTEP 0.00000 p016 PSSOLVER: 0=default 0.00000 p017 0.500000 p018 GRID < 0 --> # cells on screen -1.00000 p019 INTYPE 10.0000 p020 NORDER 0.100000E-08 p021 DIVERGENCE 0.100000E-07 p022 HELMHOLTZ 0.00000 p023 NPSCAL 0.100000E-01 p024 TOLREL 0.100000E-01 p025 TOLABS 0.600000 p026 COURANT/NTAU 3.00000 p027 TORDER 0.00000 p028 TORDER: mesh velocity (0: p28=p27) 0.00000 p029 = magnetic visc if > 0, = -1/Rm if < 0 0.00000 p030 > 0 ==> properties set in uservp() 0.00000 p031 NPERT: #perturbation modes 0.00000 p032 #BCs in re2 file, if > 0 0.00000 p033 0.00000 p034 0.00000 p035 0.00000 p036 0.00000 p037 0.00000 p038 0.00000 p039 0.00000 p040 0.00000 p041 1-->multiplicative SEMG 0.00000 p042 0=gmres/1=pcg 1.00000 p043 0=semg/1=schwarz 0.00000 p044 0=E-based/1=A-based prec. 0.00000 p045 Relaxation factor for DTFS 0.00000 p046 reserved 0.00000 p047 vnu: mesh matieral prop. 0.00000 p048 0.00000 p049 0.00000 p050 0.00000 p051 0.00000 p052 IOHIS 0.00000 p053 0.00000 p054 fixed flow rate dir: |p54|=1,2,3=x,y,z 0.00000 p055 vol.flow rate (p54>0) or Ubar (p54<0) 0.00000 p056 0.00000 p057 0.00000 p058 0.00000 p059 !=0 --> full Jac. eval. for each el. 0.00000 p060 !=0 --> init. velocity to small nonzero 0.00000 p061 0.00000 p062 >0 --> force byte_swap for output 0.00000 p063 =8 --> force 8-byte output 0.00000 p064 =1 --> perturbation restart 0.00000 p065 #iofiles (eg, 0 or 64); <0 --> sep. dirs 6.00000 p066 output : <0=ascii, else binary 6.00000 p067 restart: <0=ascii, else binary 0.00000 p068 iastep: freq for avg_all (0=iostep) 0.00000 p069 0.00000 p070 0.00000 p071 0.00000 p072 0.00000 p073 0.00000 p074 verbose Helmholtz 0.00000 p075 0.00000 p076 0.00000 p077 0.00000 p078 0.00000 p079 0.00000 p080 0.00000 p081 0.00000 p082 0.00000 p083 0.00000 p084 !=0 --> sets initial timestep if p12>0 0.00000 p085 dt ratio if p84 !=0, for timesteps>0 0.00000 p086 reserved 0.00000 p087 0.00000 p088 0.00000 p089 p89 reserved 0.00000 p090 0.00000 p091 0.00000 p092 20.0000 p093 Number of previous pressure solns saved 5.00000 p094 start projecting velocity after p94 step 5.00000 p095 start projecting pressure after p95 step 1.00000 p096 p96 u0 translational velocity (in 0.300000 p097 p97 v0 translational velocity (i 0.00000 p098 3.00000 p099 dealiasing: <0--> off/3--> old/4--> new 0.00000 p100 0.00000 p101 Number of additional modes to filter 0.00000 p102 Dump out divergence at each time step 0.00000 p103 weight of stabilizing filter (.01) 0.00000 p104 0.00000 p105 0.00000 p106 0.00000 p107 !=0 --> add to h2 array in hlmhotz eqn 0.00000 p108 0.00000 p109 0.00000 p110 0.00000 p111 0.00000 p112 0.00000 p113 0.00000 p114 0.00000 p115 0.00000 p116 !=0: x elements for fast tensor product 0.00000 p117 !=0: y elements for fast tensor product 0.00000 p118 !=0: z elements for fast tensor product 4 Lines of passive scalar data follows2 CONDUCT; 2RHOCP 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 13 LOGICAL SWITCHES FOLLOW T IFFLOW F IFHEAT T IFTRAN T F F F F F F F F F F IFNAV & IFADVC (convection in P.S. fields) F F T T T T T T T T T T IFTMSH (IF mesh for this field is T mesh) F IFAXIS F IFSTRS F IFSPLIT F IFMGRID F IFMODEL F IFKEPS F IFMVBD F IFCHAR ---------------------------------- subroutine userbc (ix,iy,iz,iside,eg) include 'SIZE' include 'TOTAL' include 'NEKUSE' integer e,eg common /myturb/ utm(lx1,ly1,lz1,lelt),vtm(lx1,ly1,lz1,lelt), ! my fluctuations $ wtm(lx1,ly1,lz1,lelt) e=gllel(eg) ... uy=vtm(ix,iy,iz,e) ux =1.0+utm(ix,iy,iz,e) uz=wtm(ix,iy,iz,e) ... -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 2 12:29:47 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 2 Sep 2016 13:29:47 -0400 Subject: [Nek5000-users] ERROR: Error reading restart header. Abort. ierr= 2 call exitt: dying ... Message-ID: Hello all, I have been getting this error message for my RESTART calculations, however using the same kind of .rea file in a different calculation (different mesh) seems to work. Any help is appreciated. .rea file is attached. I had to zip it because it exceeds the file upload size limitation. Thanks, Saikat. *Saikat Mukherjee,* *Graduate** Student,* *Engineering Science and Mechanics,* *BEAM,* *Virginia Tech.* -------------- next part -------------- An HTML attachment was scrubbed... URL: -------------- next part -------------- A non-text attachment was scrubbed... Name: g100cond.zip Type: application/zip Size: 2369575 bytes Desc: not available URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 2 14:31:05 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 2 Sep 2016 21:31:05 +0200 (CEST) Subject: [Nek5000-users] ERROR: Error reading restart header. Abort. ierr= 2 call exitt: dying ... In-Reply-To: References: Message-ID: Hi Saikat, Can you show the complete log you get when trying to run the case ? Thanks, Antoine De: nek5000-users at lists.mcs.anl.gov ?: nek5000-users at lists.mcs.anl.gov Envoy?: Vendredi 2 Septembre 2016 19:29:47 Objet: [Nek5000-users] ERROR: Error reading restart header. Abort. ierr= 2 call exitt: dying ... Hello all, I have been getting this error message for my RESTART calculations, however using the same kind of .rea file in a different calculation (different mesh) seems to work. Any help is appreciated. .rea file is attached. I had to zip it because it exceeds the file upload size limitation. Thanks, Saikat. Saikat Mukherjee, Graduate Student, Engineering Science and Mechanics, BEAM, Virginia Tech. _______________________________________________ Nek5000-users mailing list Nek5000-users at lists.mcs.anl.gov https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 2 14:40:04 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 2 Sep 2016 15:40:04 -0400 Subject: [Nek5000-users] ERROR: Error reading restart header. Abort. ierr= 2 call exitt: dying ... In-Reply-To: References: Message-ID: Hi, Thanks for the reply. Here is the full output file that contains the log. Saikat. *Saikat Mukherjee,* *Graduate** Student,* *Engineering Science and Mechanics,* *BEAM,* *Virginia Tech.* On Fri, Sep 2, 2016 at 3:31 PM, wrote: > Hi Saikat, > Can you show the complete log you get when trying to run the case ? > Thanks, > Antoine > > ------------------------------ > *De: *nek5000-users at lists.mcs.anl.gov > *?: *nek5000-users at lists.mcs.anl.gov > *Envoy?: *Vendredi 2 Septembre 2016 19:29:47 > *Objet: *[Nek5000-users] ERROR: Error reading restart header. Abort. > ierr= 2 call exitt: dying ... > > Hello all, > I have been getting this error message for my RESTART calculations, > however using the same kind of .rea file in a different calculation > (different mesh) seems to work. Any help is appreciated. .rea file is > attached. I had to zip it because it exceeds the file upload size > limitation. > > Thanks, > > Saikat. > *Saikat Mukherjee,* > *Graduate** Student,* > *Engineering Science and Mechanics,* > *BEAM,* > *Virginia Tech.* > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > > -------------- next part -------------- An HTML attachment was scrubbed... URL: -------------- next part -------------- A non-text attachment was scrubbed... Name: output Type: application/octet-stream Size: 10056 bytes Desc: not available URL: From nek5000-users at lists.mcs.anl.gov Tue Sep 6 08:39:26 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 6 Sep 2016 13:39:26 +0000 Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions Message-ID: Dear nek users, I am simulating the flow in a 7 pin bundle mesh with periodic boundary conditions in Nek5000 and set the parameters p054 and p055 to -3 and 1, respectively. With these settings, the average velocity should be 1 in the geometry. This is however not what I am seeing; the maximum velocity is around 0.32. I used the same set up for a 3-D pipe and the numerical solution behaves as expected. Does anybody has details on how the fix mass flow rate/volumetric velocity are enforced in Nek5000? Thanks, Marco From nek5000-users at lists.mcs.anl.gov Tue Sep 6 09:19:38 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 6 Sep 2016 14:19:38 +0000 Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions In-Reply-To: References: Message-ID: Hi Marco, Does this have conjugate heat transfer ? Paul ________________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 06, 2016 8:39 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions Dear nek users, I am simulating the flow in a 7 pin bundle mesh with periodic boundary conditions in Nek5000 and set the parameters p054 and p055 to -3 and 1, respectively. With these settings, the average velocity should be 1 in the geometry. This is however not what I am seeing; the maximum velocity is around 0.32. I used the same set up for a 3-D pipe and the numerical solution behaves as expected. Does anybody has details on how the fix mass flow rate/volumetric velocity are enforced in Nek5000? Thanks, Marco _______________________________________________ Nek5000-users mailing list Nek5000-users at lists.mcs.anl.gov https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users From nek5000-users at lists.mcs.anl.gov Tue Sep 6 09:44:32 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 6 Sep 2016 14:44:32 +0000 Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions In-Reply-To: References: Message-ID: Paul, there is no heat added to the flow but I do have IFHEAT set to true in the rea file. The temperature profile does not vary though. Marco > On Sep 6, 2016, at 10:19 AM, nek5000-users at lists.mcs.anl.gov wrote: > > Hi Marco, > > Does this have conjugate heat transfer ? > > Paul > > ________________________________________ > From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] > Sent: Tuesday, September 06, 2016 8:39 AM > To: nek5000-users at lists.mcs.anl.gov > Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions > > Dear nek users, > > I am simulating the flow in a 7 pin bundle mesh with periodic boundary conditions in Nek5000 and set the parameters p054 and p055 to -3 and 1, respectively. With these settings, the average velocity should be 1 in the geometry. This is however not what I am seeing; the maximum velocity is around 0.32. > > I used the same set up for a 3-D pipe and the numerical solution behaves as expected. > > Does anybody has details on how the fix mass flow rate/volumetric velocity are enforced in Nek5000? > > Thanks, > Marco > > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > From nek5000-users at lists.mcs.anl.gov Tue Sep 6 10:40:23 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 6 Sep 2016 15:40:23 +0000 Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions In-Reply-To: References: Message-ID: Also, the heat equation is only solved in the fluid domain. I am only interested in the turbulent flow without heat equation for now. Marco > On Sep 6, 2016, at 10:44 AM, nek5000-users at lists.mcs.anl.gov wrote: > > Paul, > > there is no heat added to the flow but I do have IFHEAT set to true in the rea file. The temperature profile does not vary though. > > Marco >> On Sep 6, 2016, at 10:19 AM, nek5000-users at lists.mcs.anl.gov wrote: >> >> Hi Marco, >> >> Does this have conjugate heat transfer ? >> >> Paul >> >> ________________________________________ >> From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] >> Sent: Tuesday, September 06, 2016 8:39 AM >> To: nek5000-users at lists.mcs.anl.gov >> Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions >> >> Dear nek users, >> >> I am simulating the flow in a 7 pin bundle mesh with periodic boundary conditions in Nek5000 and set the parameters p054 and p055 to -3 and 1, respectively. With these settings, the average velocity should be 1 in the geometry. This is however not what I am seeing; the maximum velocity is around 0.32. >> >> I used the same set up for a 3-D pipe and the numerical solution behaves as expected. >> >> Does anybody has details on how the fix mass flow rate/volumetric velocity are enforced in Nek5000? >> >> Thanks, >> Marco >> >> >> _______________________________________________ >> Nek5000-users mailing list >> Nek5000-users at lists.mcs.anl.gov >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users >> _______________________________________________ >> Nek5000-users mailing list >> Nek5000-users at lists.mcs.anl.gov >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users >> > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > From nek5000-users at lists.mcs.anl.gov Tue Sep 6 11:36:28 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 6 Sep 2016 16:36:28 +0000 Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions In-Reply-To: References: , Message-ID: Hi Marco, If you want to send .rea/.usr off-list, I'll take a look... Best, Paul ________________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 06, 2016 10:40 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions Also, the heat equation is only solved in the fluid domain. I am only interested in the turbulent flow without heat equation for now. Marco > On Sep 6, 2016, at 10:44 AM, nek5000-users at lists.mcs.anl.gov wrote: > > Paul, > > there is no heat added to the flow but I do have IFHEAT set to true in the rea file. The temperature profile does not vary though. > > Marco >> On Sep 6, 2016, at 10:19 AM, nek5000-users at lists.mcs.anl.gov wrote: >> >> Hi Marco, >> >> Does this have conjugate heat transfer ? >> >> Paul >> >> ________________________________________ >> From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] >> Sent: Tuesday, September 06, 2016 8:39 AM >> To: nek5000-users at lists.mcs.anl.gov >> Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions >> >> Dear nek users, >> >> I am simulating the flow in a 7 pin bundle mesh with periodic boundary conditions in Nek5000 and set the parameters p054 and p055 to -3 and 1, respectively. With these settings, the average velocity should be 1 in the geometry. This is however not what I am seeing; the maximum velocity is around 0.32. >> >> I used the same set up for a 3-D pipe and the numerical solution behaves as expected. >> >> Does anybody has details on how the fix mass flow rate/volumetric velocity are enforced in Nek5000? >> >> Thanks, >> Marco >> >> >> _______________________________________________ >> Nek5000-users mailing list >> Nek5000-users at lists.mcs.anl.gov >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users >> _______________________________________________ >> Nek5000-users mailing list >> Nek5000-users at lists.mcs.anl.gov >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users >> > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > _______________________________________________ Nek5000-users mailing list Nek5000-users at lists.mcs.anl.gov https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users From nek5000-users at lists.mcs.anl.gov Tue Sep 6 12:00:27 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 6 Sep 2016 17:00:27 +0000 Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions In-Reply-To: References: Message-ID: Paul, I emailed you on your illinoi email. There is a link to download the files. Thanks for looking into this. Marco > On Sep 6, 2016, at 12:36 PM, nek5000-users at lists.mcs.anl.gov wrote: > > > Hi Marco, > > If you want to send .rea/.usr off-list, I'll take a look... > > Best, > Paul > > ________________________________________ > From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] > Sent: Tuesday, September 06, 2016 10:40 AM > To: nek5000-users at lists.mcs.anl.gov > Subject: Re: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions > > Also, the heat equation is only solved in the fluid domain. I am only interested in the turbulent flow without heat equation for now. > > Marco >> On Sep 6, 2016, at 10:44 AM, nek5000-users at lists.mcs.anl.gov wrote: >> >> Paul, >> >> there is no heat added to the flow but I do have IFHEAT set to true in the rea file. The temperature profile does not vary though. >> >> Marco >>> On Sep 6, 2016, at 10:19 AM, nek5000-users at lists.mcs.anl.gov wrote: >>> >>> Hi Marco, >>> >>> Does this have conjugate heat transfer ? >>> >>> Paul >>> >>> ________________________________________ >>> From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] >>> Sent: Tuesday, September 06, 2016 8:39 AM >>> To: nek5000-users at lists.mcs.anl.gov >>> Subject: [Nek5000-users] constant average velocity at inlet with periodic boundary conditions >>> >>> Dear nek users, >>> >>> I am simulating the flow in a 7 pin bundle mesh with periodic boundary conditions in Nek5000 and set the parameters p054 and p055 to -3 and 1, respectively. With these settings, the average velocity should be 1 in the geometry. This is however not what I am seeing; the maximum velocity is around 0.32. >>> >>> I used the same set up for a 3-D pipe and the numerical solution behaves as expected. >>> >>> Does anybody has details on how the fix mass flow rate/volumetric velocity are enforced in Nek5000? >>> >>> Thanks, >>> Marco >>> >>> >>> _______________________________________________ >>> Nek5000-users mailing list >>> Nek5000-users at lists.mcs.anl.gov >>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users >>> _______________________________________________ >>> Nek5000-users mailing list >>> Nek5000-users at lists.mcs.anl.gov >>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users >>> >> >> _______________________________________________ >> Nek5000-users mailing list >> Nek5000-users at lists.mcs.anl.gov >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users >> > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > From nek5000-users at lists.mcs.anl.gov Wed Sep 7 19:37:54 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Wed, 7 Sep 2016 20:37:54 -0400 Subject: [Nek5000-users] Tools Compilation Error Message-ID: Hi All, Just thought I'd let everyone know (I assume this has been seen) that in the latest GIT or SVN version, the tools compilation fails when the maketools script gets to postnek, and the reference to the file blas.f cannot be found; need to change the reference in the postnek makefile from "../nek/.." to "../core/.." Thanks, Murph From nek5000-users at lists.mcs.anl.gov Thu Sep 8 07:52:33 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Thu, 08 Sep 2016 12:52:33 +0000 Subject: [Nek5000-users] Tools Compilation Error In-Reply-To: References: Message-ID: Hi Murph, Thanks for pointing this out. I believe we fixed this in the "develop" branch a few weeks back: https://github.com/Nek5000/Nek5000/commit/3ff04ccb36446f001834d67b4ebfe549fa1ac6f3 The changes haven't been merged into the "master" branch since we are still finalizing the release. You should expect to see it soon. For now, if you'd like to see this and other bug fixes, you're welcome to use the "develop" branch. Best, Ron On Wed, Sep 7, 2016 at 9:24 PM wrote: > Hi All, > > Just thought I'd let everyone know (I assume this has been seen) that in > the latest GIT or SVN version, the tools compilation fails when the > maketools script gets to postnek, and the reference to the file blas.f > cannot be found; need to change the reference in the postnek makefile > from "../nek/.." to "../core/.." > > > Thanks, > > Murph > > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users > -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 9 09:51:02 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 9 Sep 2016 14:51:02 +0000 Subject: [Nek5000-users] Time of restart Message-ID: Dear Nek users, I?m using the restart option in *.rea. How can I force the restart time to 0, instead of the time in restarting file. The file to restart has format of *.f0000 Thank you, Peng From nek5000-users at lists.mcs.anl.gov Fri Sep 9 11:13:30 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 9 Sep 2016 16:13:30 +0000 Subject: [Nek5000-users] Time of restart In-Reply-To: References: Message-ID: Hi Peng, I usually do the following in the .usr file: in userchk .... if (step.eq.0) time=0 ...You do have to remember to comment this out for subsequent restarts, however. Paul ________________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Friday, September 09, 2016 9:51 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Time of restart Dear Nek users, I?m using the restart option in *.rea. How can I force the restart time to 0, instead of the time in restarting file. The file to restart has format of *.f0000 Thank you, Peng _______________________________________________ Nek5000-users mailing list Nek5000-users at lists.mcs.anl.gov https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users From nek5000-users at lists.mcs.anl.gov Fri Sep 9 16:25:24 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 9 Sep 2016 21:25:24 +0000 Subject: [Nek5000-users] Time of restart In-Reply-To: References: Message-ID: Thanks Paul! Peng > On Sep 9, 2016, at 1:00 PM, nek5000-users-request at lists.mcs.anl.gov wrote: > > Send Nek5000-users mailing list submissions to > nek5000-users at lists.mcs.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.mcs.anl.gov_mailman_listinfo_nek5000-2Dusers&d=DQICAg&c=y2w-uYmhgFWijp_IQN0DhA&r=QEl5evD27KmYmPJRHh_RJPXwtG0VKYwu68jKU6Xd1hw&m=EboqzcGMC8bHF11qSx9LDsKHqyLyyiYVSjbX8lusxwQ&s=842Qrk3uY0A69nu48HPLXZeRqUhmeh5ZvD-PYHs1VJI&e= > or, via email, send a message with subject or body 'help' to > nek5000-users-request at lists.mcs.anl.gov > > You can reach the person managing the list at > nek5000-users-owner at lists.mcs.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Nek5000-users digest..." > > > Today's Topics: > > 1. Time of restart (nek5000-users at lists.mcs.anl.gov) > 2. Re: Time of restart (nek5000-users at lists.mcs.anl.gov) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Fri, 9 Sep 2016 14:51:02 +0000 > From: nek5000-users at lists.mcs.anl.gov > To: "nek5000-users at lists.mcs.anl.gov" > > Subject: [Nek5000-users] Time of restart > Message-ID: > > Content-Type: text/plain; charset="utf-8" > > Dear Nek users, > > I?m using the restart option in *.rea. > How can I force the restart time to 0, instead of the time in restarting file. > The file to restart has format of *.f0000 > > Thank you, > Peng > > > ------------------------------ > > Message: 2 > Date: Fri, 9 Sep 2016 16:13:30 +0000 > From: nek5000-users at lists.mcs.anl.gov > To: "nek5000-users at lists.mcs.anl.gov" > > Subject: Re: [Nek5000-users] Time of restart > Message-ID: > > Content-Type: text/plain; charset="Windows-1252" > > > Hi Peng, > > I usually do the following in the .usr file: > > in userchk .... > > > if (step.eq.0) time=0 > > ...You do have to remember to comment this out for subsequent restarts, however. > > Paul > > ________________________________________ > From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] > Sent: Friday, September 09, 2016 9:51 AM > To: nek5000-users at lists.mcs.anl.gov > Subject: [Nek5000-users] Time of restart > > Dear Nek users, > > I?m using the restart option in *.rea. > How can I force the restart time to 0, instead of the time in restarting file. > The file to restart has format of *.f0000 > > Thank you, > Peng > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.mcs.anl.gov_mailman_listinfo_nek5000-2Dusers&d=DQICAg&c=y2w-uYmhgFWijp_IQN0DhA&r=QEl5evD27KmYmPJRHh_RJPXwtG0VKYwu68jKU6Xd1hw&m=EboqzcGMC8bHF11qSx9LDsKHqyLyyiYVSjbX8lusxwQ&s=842Qrk3uY0A69nu48HPLXZeRqUhmeh5ZvD-PYHs1VJI&e= > > ------------------------------ > > _______________________________________________ > Nek5000-users mailing list > Nek5000-users at lists.mcs.anl.gov > https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.mcs.anl.gov_mailman_listinfo_nek5000-2Dusers&d=DQICAg&c=y2w-uYmhgFWijp_IQN0DhA&r=QEl5evD27KmYmPJRHh_RJPXwtG0VKYwu68jKU6Xd1hw&m=EboqzcGMC8bHF11qSx9LDsKHqyLyyiYVSjbX8lusxwQ&s=842Qrk3uY0A69nu48HPLXZeRqUhmeh5ZvD-PYHs1VJI&e= > > > End of Nek5000-users Digest, Vol 91, Issue 8 > ******************************************** From nek5000-users at lists.mcs.anl.gov Tue Sep 13 16:30:41 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 13 Sep 2016 21:30:41 +0000 Subject: [Nek5000-users] recycling BC Message-ID: I'm trying to setup a problem with recycling BC and am getting a series of errors. First in 'get_shift' I hit the check : npmax = iglmax(npts,1) ! max RBC pts/core if (npmax.gt.lpart) call exitti( $ 'set_inflow err: increase lpart in SIZE$',npmax) After I increased lpart in SIZE to satisfy the above, the code aborted complaining that the problem is too large and is suggesting to recompile with lelt = total number of elements. What is the role of this check? Thanks for looking into this. -emilian -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 16 01:03:22 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 16 Sep 2016 02:03:22 -0400 Subject: [Nek5000-users] Profile points in Postnek Message-ID: Hello all, How do you change the default maximum number of profile points in Postnek? I have the maximum set at 4000. Thanks, Saikat. Saikat Mukherjee, Graduate Student, Engineering Science and Mechanics, BEAM, Virginia Tech. -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 16 07:44:13 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 16 Sep 2016 12:44:13 +0000 Subject: [Nek5000-users] Profile points in Postnek In-Reply-To: References: Message-ID: Hi Saikat, You would need to change mxpro in nek5000/tools/postnek/basicsp.inc to a larger value. (Max is currently 4000 points.) Then cd cd nek5000/tools maketools postnek then, in postx: SET ATTRIBUTE SET RESOLUTION PROFILE POINTS and type in the new number that you want. It will take min of that value with whatever you set mxpro to be in the basicsp.inc file. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Friday, September 16, 2016 1:03 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Profile points in Postnek Hello all, How do you change the default maximum number of profile points in Postnek? I have the maximum set at 4000. Thanks, Saikat. Saikat Mukherjee, Graduate Student, Engineering Science and Mechanics, BEAM, Virginia Tech. -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Mon Sep 19 09:08:20 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Mon, 19 Sep 2016 14:08:20 +0000 Subject: [Nek5000-users] IFMGRID and IFMVBD Message-ID: Dear Nek users, In *.rea file, there are two logical switches for free surface flow, i.e. IFMGRID and IFMVBD. Should both of them be set to true in simulating free surface flow? Thank you, Peng From nek5000-users at lists.mcs.anl.gov Tue Sep 20 07:24:19 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 20 Sep 2016 12:24:19 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Message-ID: Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Tue Sep 20 09:02:03 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 20 Sep 2016 14:02:03 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: Message-ID: Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Tue Sep 20 09:32:17 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 20 Sep 2016 14:32:17 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: Message-ID: Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax - xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Tue Sep 20 09:41:00 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 20 Sep 2016 14:41:00 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: , Message-ID: Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax ? xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Tue Sep 20 09:55:40 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 20 Sep 2016 14:55:40 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: , Message-ID: Paul, I am not using the usrdat2 sub-routine for now. But in any case, I will set p59 = 1. I am only using the function ffx in the sub-routine userf. But I checked the vol_flow routine and could not find anything that should affect ffx in the angled domain. So I will keep it. Do you agree? Best regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:43 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax - xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Tue Sep 20 10:46:21 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 20 Sep 2016 15:46:21 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: , , Message-ID: Hi Pradyumna, If you are using p54/p55, you should set ffx (ffy,ffz) to 0. Nek will adjust the mean pressure drop to sustain your requested flow rate. You can find what this is, as a function of time, by: grep volf logfile Column 1 is step number Column 2 is time Column 3 is ffx (unless you prescribed ffx, then c2 will be ffx - what you prescribed). Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:55 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, I am not using the usrdat2 sub-routine for now. But in any case, I will set p59 = 1. I am only using the function ffx in the sub-routine userf. But I checked the vol_flow routine and could not find anything that should affect ffx in the angled domain. So I will keep it. Do you agree? Best regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:43 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax ? xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Tue Sep 20 10:58:38 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 20 Sep 2016 15:58:38 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: , , Message-ID: Paul, Thank you I will do that. Best regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 5:48 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, If you are using p54/p55, you should set ffx (ffy,ffz) to 0. Nek will adjust the mean pressure drop to sustain your requested flow rate. You can find what this is, as a function of time, by: grep volf logfile Column 1 is step number Column 2 is time Column 3 is ffx (unless you prescribed ffx, then c2 will be ffx - what you prescribed). Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:55 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, I am not using the usrdat2 sub-routine for now. But in any case, I will set p59 = 1. I am only using the function ffx in the sub-routine userf. But I checked the vol_flow routine and could not find anything that should affect ffx in the angled domain. So I will keep it. Do you agree? Best regards, c From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:43 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax - xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Thu Sep 22 04:25:19 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Thu, 22 Sep 2016 09:25:19 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Message-ID: Hi Neks, I had recently clarified a few issues on the forum regarding the flow rate and the mean velocity parameters p54 and p55. There are still a few issues and therefore, for convenience, I am replying to the same thread. Paul, like you had suggested I ran a simulation with the p54 set to -1.0 and the p55 set to 1.0 (because I want the bulk mean velocity in the channel to be 1 , so as to make the viscosity \nu = 1 / Re). This I did with two domains at two different angles of 30 degrees and 60 degrees (a quick screenshot is attached in the mail. Note this is a 3D simulation, the image shows view perpendicular to the z-axis). The perpendicular distance between the walls normal to the y-axis are the same between these domains, as are all the other simulation parameters, except for the mesh points (of course, since the domains are different). The ffx variable in the userf sub-routine is set to zero, and as far as I can say, there is nothing else in the case files that could be affecting the mass flow rates or the velocity in this simulation. However when I run the simulation for the two different domains with the same p55, I am still ending up with different volume flow rates ( and therefore different turbulent Reynolds numbers, Re_\tau, which is my ultimate target). I could not understand, what it is that is causing this. Do you, or anybody else have any inputs on why this might be happening? Here are a few lines, of the last few time steps, from the logfile of the 30 degrees domain containing the volume flow rate: 161133 0.1099986E+04 4.03381E-03 9.43269E-05 5.39728E+00 5.39738E+00 volflow X 161134 0.1099994E+04 4.03312E-03 9.43107E-05 5.39728E+00 5.39738E+00 volflow X 161135 0.1100001E+04 4.03279E-03 7.99447E-05 5.39730E+00 5.39738E+00 volflow X Similar lines for the 60 degrees domain: 86405 0.1099983E+04 3.90944E-03 1.07987E-04 4.13041E+00 4.13052E+00 volflow X 86406 0.1099996E+04 3.91068E-03 1.08021E-04 4.13041E+00 4.13052E+00 volflow X 86407 0.1100005E+04 3.91126E-03 9.15895E-05 4.13043E+00 4.13052E+00 volflow X Thanks and regards, Pradyumna TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 6:01 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, Thank you I will do that. Best regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 5:48 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, If you are using p54/p55, you should set ffx (ffy,ffz) to 0. Nek will adjust the mean pressure drop to sustain your requested flow rate. You can find what this is, as a function of time, by: grep volf logfile Column 1 is step number Column 2 is time Column 3 is ffx (unless you prescribed ffx, then c2 will be ffx - what you prescribed). Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:55 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, I am not using the usrdat2 sub-routine for now. But in any case, I will set p59 = 1. I am only using the function ffx in the sub-routine userf. But I checked the vol_flow routine and could not find anything that should affect ffx in the angled domain. So I will keep it. Do you agree? Best regards, c From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:43 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax - xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: -------------- next part -------------- A non-text attachment was scrubbed... Name: mesh.png Type: image/png Size: 38883 bytes Desc: mesh.png URL: From nek5000-users at lists.mcs.anl.gov Thu Sep 22 08:15:10 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Thu, 22 Sep 2016 13:15:10 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: Message-ID: Hi Pradyumna, Right. The volf reported in the fixed-flow rate routine computes \int u dV / L-domain In your case, it can't figure out L-domain, which needs to be the periodic pitch, rather than the naive xmax-xmin, which is what it uses. This is the same reason I suggested switching to prescribing Ubar, which is computed as: Ubar = \int u dV / \int 1 dV = \int u dV / volume [ This definition is also problematic in other cases.. but it's ok here.] So, your volumetric flow is likely ok --- I just ran tests in 2d and 3d to verify --- but you'll need to correct for your domain length according to the above. Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Thursday, September 22, 2016 4:25 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I had recently clarified a few issues on the forum regarding the flow rate and the mean velocity parameters p54 and p55. There are still a few issues and therefore, for convenience, I am replying to the same thread. Paul, like you had suggested I ran a simulation with the p54 set to -1.0 and the p55 set to 1.0 (because I want the bulk mean velocity in the channel to be 1 , so as to make the viscosity \nu = 1 / Re). This I did with two domains at two different angles of 30 degrees and 60 degrees (a quick screenshot is attached in the mail. Note this is a 3D simulation, the image shows view perpendicular to the z-axis). The perpendicular distance between the walls normal to the y-axis are the same between these domains, as are all the other simulation parameters, except for the mesh points (of course, since the domains are different). The ffx variable in the userf sub-routine is set to zero, and as far as I can say, there is nothing else in the case files that could be affecting the mass flow rates or the velocity in this simulation. However when I run the simulation for the two different domains with the same p55, I am still ending up with different volume flow rates ( and therefore different turbulent Reynolds numbers, Re_\tau, which is my ultimate target). I could not understand, what it is that is causing this. Do you, or anybody else have any inputs on why this might be happening? Here are a few lines, of the last few time steps, from the logfile of the 30 degrees domain containing the volume flow rate: 161133 0.1099986E+04 4.03381E-03 9.43269E-05 5.39728E+00 5.39738E+00 volflow X 161134 0.1099994E+04 4.03312E-03 9.43107E-05 5.39728E+00 5.39738E+00 volflow X 161135 0.1100001E+04 4.03279E-03 7.99447E-05 5.39730E+00 5.39738E+00 volflow X Similar lines for the 60 degrees domain: 86405 0.1099983E+04 3.90944E-03 1.07987E-04 4.13041E+00 4.13052E+00 volflow X 86406 0.1099996E+04 3.91068E-03 1.08021E-04 4.13041E+00 4.13052E+00 volflow X 86407 0.1100005E+04 3.91126E-03 9.15895E-05 4.13043E+00 4.13052E+00 volflow X Thanks and regards, Pradyumna TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 6:01 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, Thank you I will do that. Best regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 5:48 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, If you are using p54/p55, you should set ffx (ffy,ffz) to 0. Nek will adjust the mean pressure drop to sustain your requested flow rate. You can find what this is, as a function of time, by: grep volf logfile Column 1 is step number Column 2 is time Column 3 is ffx (unless you prescribed ffx, then c2 will be ffx - what you prescribed). Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:55 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, I am not using the usrdat2 sub-routine for now. But in any case, I will set p59 = 1. I am only using the function ffx in the sub-routine userf. But I checked the vol_flow routine and could not find anything that should affect ffx in the angled domain. So I will keep it. Do you agree? Best regards, c From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:43 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax ? xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Thu Sep 22 08:43:54 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Thu, 22 Sep 2016 13:43:54 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: Message-ID: Paul, Ah ok. Do I also then have to change the object definition somewhere which is involved in the calculation of the drag (and hence the Re_\tau) in the sub-routine drag_calc? Because the results of the drag are also varying with the angling of the domain, and hence the calculation of the Re_\tau is changing, and that is the main criterion that I have to characterize the flow. Thanks and regards, Pradyumna TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Thursday, September 22, 2016 3:16 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Right. The volf reported in the fixed-flow rate routine computes \int u dV / L-domain In your case, it can't figure out L-domain, which needs to be the periodic pitch, rather than the naive xmax-xmin, which is what it uses. This is the same reason I suggested switching to prescribing Ubar, which is computed as: Ubar = \int u dV / \int 1 dV = \int u dV / volume [ This definition is also problematic in other cases.. but it's ok here.] So, your volumetric flow is likely ok --- I just ran tests in 2d and 3d to verify --- but you'll need to correct for your domain length according to the above. Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Thursday, September 22, 2016 4:25 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I had recently clarified a few issues on the forum regarding the flow rate and the mean velocity parameters p54 and p55. There are still a few issues and therefore, for convenience, I am replying to the same thread. Paul, like you had suggested I ran a simulation with the p54 set to -1.0 and the p55 set to 1.0 (because I want the bulk mean velocity in the channel to be 1 , so as to make the viscosity \nu = 1 / Re). This I did with two domains at two different angles of 30 degrees and 60 degrees (a quick screenshot is attached in the mail. Note this is a 3D simulation, the image shows view perpendicular to the z-axis). The perpendicular distance between the walls normal to the y-axis are the same between these domains, as are all the other simulation parameters, except for the mesh points (of course, since the domains are different). The ffx variable in the userf sub-routine is set to zero, and as far as I can say, there is nothing else in the case files that could be affecting the mass flow rates or the velocity in this simulation. However when I run the simulation for the two different domains with the same p55, I am still ending up with different volume flow rates ( and therefore different turbulent Reynolds numbers, Re_\tau, which is my ultimate target). I could not understand, what it is that is causing this. Do you, or anybody else have any inputs on why this might be happening? Here are a few lines, of the last few time steps, from the logfile of the 30 degrees domain containing the volume flow rate: 161133 0.1099986E+04 4.03381E-03 9.43269E-05 5.39728E+00 5.39738E+00 volflow X 161134 0.1099994E+04 4.03312E-03 9.43107E-05 5.39728E+00 5.39738E+00 volflow X 161135 0.1100001E+04 4.03279E-03 7.99447E-05 5.39730E+00 5.39738E+00 volflow X Similar lines for the 60 degrees domain: 86405 0.1099983E+04 3.90944E-03 1.07987E-04 4.13041E+00 4.13052E+00 volflow X 86406 0.1099996E+04 3.91068E-03 1.08021E-04 4.13041E+00 4.13052E+00 volflow X 86407 0.1100005E+04 3.91126E-03 9.15895E-05 4.13043E+00 4.13052E+00 volflow X Thanks and regards, Pradyumna TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 6:01 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, Thank you I will do that. Best regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 5:48 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, If you are using p54/p55, you should set ffx (ffy,ffz) to 0. Nek will adjust the mean pressure drop to sustain your requested flow rate. You can find what this is, as a function of time, by: grep volf logfile Column 1 is step number Column 2 is time Column 3 is ffx (unless you prescribed ffx, then c2 will be ffx - what you prescribed). Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:55 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, I am not using the usrdat2 sub-routine for now. But in any case, I will set p59 = 1. I am only using the function ffx in the sub-routine userf. But I checked the vol_flow routine and could not find anything that should affect ffx in the angled domain. So I will keep it. Do you agree? Best regards, c From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:43 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax - xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Thu Sep 22 09:07:32 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Thu, 22 Sep 2016 14:07:32 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: , Message-ID: I shouldn't think you have to change that, it computes its own area. You should be aware, that shearing a domain reduces the effective mesh resolution. This is its main impact on the solution quality --- it's not the angle of the mesh per se (though that _might_ be an issue at severe angles, but I don't thing so). Why? First - a shear results in constant metrics and Jacobian; so it doesn't introduce high wave-number components into the integrands in the weighted residual terms. Second - Consider a shear of the form x = r + s*shear, y = s A unit length in s has now been translated from dL = (dy/ds) *ds = dy, to dL = (dy/ds) + (dx/ds) ] * ds Total proportional change of sqrt( 1 + shear^2 ). Pictorially, If you have k waves in x and y and a polynomial of deg N in x and y, you are resolving k waves with N modes. Now, in the sheared case you will encounter many more modes along the diagonal than if you cut straight across. Assuming isotropy, the number will increase according to the increased length of the edge. So, to recover the same resolution along that edge, you need to add more elements in the y direction. ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Thursday, September 22, 2016 8:43 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, Ah ok. Do I also then have to change the object definition somewhere which is involved in the calculation of the drag (and hence the Re_\tau) in the sub-routine drag_calc? Because the results of the drag are also varying with the angling of the domain, and hence the calculation of the Re_\tau is changing, and that is the main criterion that I have to characterize the flow. Thanks and regards, Pradyumna TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Thursday, September 22, 2016 3:16 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Right. The volf reported in the fixed-flow rate routine computes \int u dV / L-domain In your case, it can't figure out L-domain, which needs to be the periodic pitch, rather than the naive xmax-xmin, which is what it uses. This is the same reason I suggested switching to prescribing Ubar, which is computed as: Ubar = \int u dV / \int 1 dV = \int u dV / volume [ This definition is also problematic in other cases.. but it's ok here.] So, your volumetric flow is likely ok --- I just ran tests in 2d and 3d to verify --- but you'll need to correct for your domain length according to the above. Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Thursday, September 22, 2016 4:25 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I had recently clarified a few issues on the forum regarding the flow rate and the mean velocity parameters p54 and p55. There are still a few issues and therefore, for convenience, I am replying to the same thread. Paul, like you had suggested I ran a simulation with the p54 set to -1.0 and the p55 set to 1.0 (because I want the bulk mean velocity in the channel to be 1 , so as to make the viscosity \nu = 1 / Re). This I did with two domains at two different angles of 30 degrees and 60 degrees (a quick screenshot is attached in the mail. Note this is a 3D simulation, the image shows view perpendicular to the z-axis). The perpendicular distance between the walls normal to the y-axis are the same between these domains, as are all the other simulation parameters, except for the mesh points (of course, since the domains are different). The ffx variable in the userf sub-routine is set to zero, and as far as I can say, there is nothing else in the case files that could be affecting the mass flow rates or the velocity in this simulation. However when I run the simulation for the two different domains with the same p55, I am still ending up with different volume flow rates ( and therefore different turbulent Reynolds numbers, Re_\tau, which is my ultimate target). I could not understand, what it is that is causing this. Do you, or anybody else have any inputs on why this might be happening? Here are a few lines, of the last few time steps, from the logfile of the 30 degrees domain containing the volume flow rate: 161133 0.1099986E+04 4.03381E-03 9.43269E-05 5.39728E+00 5.39738E+00 volflow X 161134 0.1099994E+04 4.03312E-03 9.43107E-05 5.39728E+00 5.39738E+00 volflow X 161135 0.1100001E+04 4.03279E-03 7.99447E-05 5.39730E+00 5.39738E+00 volflow X Similar lines for the 60 degrees domain: 86405 0.1099983E+04 3.90944E-03 1.07987E-04 4.13041E+00 4.13052E+00 volflow X 86406 0.1099996E+04 3.91068E-03 1.08021E-04 4.13041E+00 4.13052E+00 volflow X 86407 0.1100005E+04 3.91126E-03 9.15895E-05 4.13043E+00 4.13052E+00 volflow X Thanks and regards, Pradyumna TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 6:01 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, Thank you I will do that. Best regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 5:48 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, If you are using p54/p55, you should set ffx (ffy,ffz) to 0. Nek will adjust the mean pressure drop to sustain your requested flow rate. You can find what this is, as a function of time, by: grep volf logfile Column 1 is step number Column 2 is time Column 3 is ffx (unless you prescribed ffx, then c2 will be ffx - what you prescribed). Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:55 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, I am not using the usrdat2 sub-routine for now. But in any case, I will set p59 = 1. I am only using the function ffx in the sub-routine userf. But I checked the vol_flow routine and could not find anything that should affect ffx in the angled domain. So I will keep it. Do you agree? Best regards, c From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:43 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax ? xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 23 07:25:01 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 23 Sep 2016 12:25:01 +0000 Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes In-Reply-To: References: , Message-ID: Paul, Thank you for the explanation of the impact on the quality of the simulation due to domain shear. I am actually planning to investigate this more in detail. Are there any books, articles, etc. that you might suggest, that elaborate on the effect of mesh/ domain distortion on the solution quality and error, for spectral element codes, in general, and maybe, NEK5000 in particular? Best, Pradyumna From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Thursday, September 22, 2016 4:09 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes I shouldn't think you have to change that, it computes its own area. You should be aware, that shearing a domain reduces the effective mesh resolution. This is its main impact on the solution quality --- it's not the angle of the mesh per se (though that _might_ be an issue at severe angles, but I don't thing so). Why? First - a shear results in constant metrics and Jacobian; so it doesn't introduce high wave-number components into the integrands in the weighted residual terms. Second - Consider a shear of the form x = r + s*shear, y = s A unit length in s has now been translated from dL = (dy/ds) *ds = dy, to dL = (dy/ds) + (dx/ds) ] * ds Total proportional change of sqrt( 1 + shear^2 ). Pictorially, If you have k waves in x and y and a polynomial of deg N in x and y, you are resolving k waves with N modes. Now, in the sheared case you will encounter many more modes along the diagonal than if you cut straight across. Assuming isotropy, the number will increase according to the increased length of the edge. So, to recover the same resolution along that edge, you need to add more elements in the y direction. ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Thursday, September 22, 2016 8:43 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, Ah ok. Do I also then have to change the object definition somewhere which is involved in the calculation of the drag (and hence the Re_\tau) in the sub-routine drag_calc? Because the results of the drag are also varying with the angling of the domain, and hence the calculation of the Re_\tau is changing, and that is the main criterion that I have to characterize the flow. Thanks and regards, Pradyumna TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Thursday, September 22, 2016 3:16 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Right. The volf reported in the fixed-flow rate routine computes \int u dV / L-domain In your case, it can't figure out L-domain, which needs to be the periodic pitch, rather than the naive xmax-xmin, which is what it uses. This is the same reason I suggested switching to prescribing Ubar, which is computed as: Ubar = \int u dV / \int 1 dV = \int u dV / volume [ This definition is also problematic in other cases.. but it's ok here.] So, your volumetric flow is likely ok --- I just ran tests in 2d and 3d to verify --- but you'll need to correct for your domain length according to the above. Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Thursday, September 22, 2016 4:25 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I had recently clarified a few issues on the forum regarding the flow rate and the mean velocity parameters p54 and p55. There are still a few issues and therefore, for convenience, I am replying to the same thread. Paul, like you had suggested I ran a simulation with the p54 set to -1.0 and the p55 set to 1.0 (because I want the bulk mean velocity in the channel to be 1 , so as to make the viscosity \nu = 1 / Re). This I did with two domains at two different angles of 30 degrees and 60 degrees (a quick screenshot is attached in the mail. Note this is a 3D simulation, the image shows view perpendicular to the z-axis). The perpendicular distance between the walls normal to the y-axis are the same between these domains, as are all the other simulation parameters, except for the mesh points (of course, since the domains are different). The ffx variable in the userf sub-routine is set to zero, and as far as I can say, there is nothing else in the case files that could be affecting the mass flow rates or the velocity in this simulation. However when I run the simulation for the two different domains with the same p55, I am still ending up with different volume flow rates ( and therefore different turbulent Reynolds numbers, Re_\tau, which is my ultimate target). I could not understand, what it is that is causing this. Do you, or anybody else have any inputs on why this might be happening? Here are a few lines, of the last few time steps, from the logfile of the 30 degrees domain containing the volume flow rate: 161133 0.1099986E+04 4.03381E-03 9.43269E-05 5.39728E+00 5.39738E+00 volflow X 161134 0.1099994E+04 4.03312E-03 9.43107E-05 5.39728E+00 5.39738E+00 volflow X 161135 0.1100001E+04 4.03279E-03 7.99447E-05 5.39730E+00 5.39738E+00 volflow X Similar lines for the 60 degrees domain: 86405 0.1099983E+04 3.90944E-03 1.07987E-04 4.13041E+00 4.13052E+00 volflow X 86406 0.1099996E+04 3.91068E-03 1.08021E-04 4.13041E+00 4.13052E+00 volflow X 86407 0.1100005E+04 3.91126E-03 9.15895E-05 4.13043E+00 4.13052E+00 volflow X Thanks and regards, Pradyumna TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 6:01 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, Thank you I will do that. Best regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 5:48 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, If you are using p54/p55, you should set ffx (ffy,ffz) to 0. Nek will adjust the mean pressure drop to sustain your requested flow rate. You can find what this is, as a function of time, by: grep volf logfile Column 1 is step number Column 2 is time Column 3 is ffx (unless you prescribed ffx, then c2 will be ffx - what you prescribed). Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:55 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Paul, I am not using the usrdat2 sub-routine for now. But in any case, I will set p59 = 1. I am only using the function ffx in the sub-routine userf. But I checked the vol_flow routine and could not find anything that should affect ffx in the angled domain. So I will keep it. Do you agree? Best regards, c From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:43 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pradyumna, Periodicity is pretty robust in nek. As long as the pair of periodic faces has the same normal vector and are of the same area, then it should work. Yes - I believe that using the correct Ubar will work for you. Another point, which I discovered just last week: If you are applying a shear in usrdat2 (which would be a normal thing to do), you need to make certain you set param(59)=1 in the .usr file. This turns off the "fast" operator evaluation that is valid only for element that are proper rectilinear bricks. The code detects such bricks when they are read from the .rea file, but the mechanism uses information that is not touched by standard morphing procedures. I'm working on a fix for this, but for now you should set param(59)=1, which will turn off the fast mode. Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 9:32 AM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Paul, Thank you for your reply. I am indeed using the flow rate parameter, that is p54 > 0. From your reply, then can I assume that prescribing the mean velocity should lead to reliable results? Also it struck me when reading your reply, so I am directly asking you. If the Lx =xmax - xmin is incorrect for an angled domain, then will it in anyway affect the periodic boundary conditions. I still want the same periodic conditions, as they were in the orthogonal turbulent channel flow case (periodic about the x-axis direction). That is the velocity profile in the right-most elements should be implanted onto the left-most profile. Will this happen reliably or could there be any factors that might cause a problem? Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering From: nek5000-users-bounces at lists.mcs.anl.gov [mailto:nek5000-users-bounces at lists.mcs.anl.gov] On Behalf Of nek5000-users at lists.mcs.anl.gov Sent: Tuesday, September 20, 2016 4:04 PM To: nek5000-users at lists.mcs.anl.gov Subject: Re: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Pardyumna, Nek supports two fixed flow-rate modes: .prescribed flow rate .prescribed average velocity. You toggle between these modes according to the sign of parameter 54. If p54 < 0, you are prescribing mean velocity If p54 > 0, you are prescribing flow rate. The flow rate may not work in your case because of the fact that your domain "length" ( := xmax - xmin) is not the same as your periodic pitch. The mean velocity is computed is: \int u dV / \int dV and I believe that should work OK. Flow rate needs an estimate of the length of the domain Q(x) = \int_A u dA = constant (by mass conservation) Q := (1/Lx) \int_0^Lx Q(x) dx = (1/Lx) * \int_Omega u dV In your case, Lx is the periodic pitch, and not equal to (xmax-xmin). However, Nek does not know how to find the periodic pitch. It is using Lx = xmax-xmin, which is incorrect for your geometry. Which one are your using? Best, Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Tuesday, September 20, 2016 7:24 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Drag calculation and mass flow rate with angled meshes Hi Neks, I am trying to run a simulation case similar to the turbulent channel flow case. I initially ran a simulation on the normal turbulent channel flow domain (with the geometry like the fig on the left). I used the parameter p55 in the rea file to ensure that the bulk velocity of the flow is 1 in the domain, and used the parameter p02 to set the turbulent Reynolds number, Re_tau to my required value of 180. I used the sub-routine drag_calc to find the mean shear on the wall, from which I calculated the shear stress and then the Re_tau and u_tau values. However, recently I was trying the same thing on a slightly different domain (fig to the right). --------------------------------------------------------------------- --------------------------------------------------------------------- | | / / ^ Y | | / / | | | / / |_____> X | | / / | | / / --------------------------------------------------------------------- --------------------------------------------------------------------- This domain is almost the same as the first except now there is an angle of 30 degrees in the mesh grid about the z-axis. Please note that the perpendicular distance between the walls normal to the y-direction remains the same for both the domains. In this domain if I use the same p55 and p02 parameters that I use for the orthogonal domain, then Re_tau, calculated as described above, is increasing to higher values (~220). If I reduce the parameter p55 to lesser values, then the Re_tau value is restored to 180. I could not figure out why exactly this was happening, and whether this difference is now because my way of calculating the Re_tau is not valid anymore in the angled domain. Or is the change because the mass flow rate is actually higher in the angled domain? If the case is latter, then why is the mass flow rate increasing just due to the angling of the mesh? I went through the sub-routines drag_calc, vol_flow and set_obj (to see if the integral object needs to be changed) in moderate detail, but could not figure out the reasons for this. Any help in this might be appreciated, as I want to establish the reason, so that I can trust the accuracy of the results of this simulation. Thanks and regards, Pradyumna M K Prasad TU Delft, Student: Masters in Aerospace Engineering -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 23 08:46:43 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 23 Sep 2016 13:46:43 +0000 Subject: [Nek5000-users] Definition of variables in the .usr file? Message-ID: Dear All, Is there any documentation of all variables that I have available in the .usr file? For example, in the User Guide it is explained you to modify a mesh for a straight pipe into a pipe with a width that varies along it. You use then * The variable "ntot". Which I guess is the number of vertices, but i it? * The variable "ym1", which seems to be a 4D tensor. Here you change the element ym1(i,1,1,1) for i = 1,ntot. Is this the y-position of the verices? What alse does ym1 contain? These and other variables are variables that I would appreciate to know the definition of. Is it available somwhere? Best, Johan -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 23 09:56:30 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 23 Sep 2016 14:56:30 +0000 Subject: [Nek5000-users] Definition of variables in the .usr file? In-Reply-To: References: Message-ID: Dear Johan, Virtually _all_ the variables are available because of the include 'TOTAL' statement. Geometry is in arrays xm1,ym1,zm1. N^3 x Nel is the data layout for all arrays, save for surface variables such as unit normals and surface area of each face of each element. (unx,uny,unz,area). Paul ________________________________ From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov] Sent: Friday, September 23, 2016 8:46 AM To: nek5000-users at lists.mcs.anl.gov Subject: [Nek5000-users] Definition of variables in the .usr file? Dear All, Is there any documentation of all variables that I have available in the .usr file? For example, in the User Guide it is explained you to modify a mesh for a straight pipe into a pipe with a width that varies along it. You use then * The variable "ntot". Which I guess is the number of vertices, but i it? * The variable "ym1", which seems to be a 4D tensor. Here you change the element ym1(i,1,1,1) for i = 1,ntot. Is this the y-position of the verices? What alse does ym1 contain? These and other variables are variables that I would appreciate to know the definition of. Is it available somwhere? Best, Johan -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Fri Sep 23 15:36:33 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Fri, 23 Sep 2016 16:36:33 -0400 Subject: [Nek5000-users] Error in Postnek for passive scalars. Message-ID: Hello everyone, I am encountering an error when I am doing the SET QUANTITY in postnek. I have 3 passive scalars, and in the SET QUANTITY, I should get them as PS 1, PS 2 and PS 3. Instead I am getting I, E E E, E E E --- these kind of notations. When I try to set either one of them as my Quantity I end up with nothing. Also the Postnek window has E E E E E E...I on top of it, which I have never seen before. I think it's some sort of an error. Has anyone else encountered this? Thanks, Saikat. Saikat Mukherjee, Graduate Student, Engineering Science and Mechanics, BEAM, Virginia Tech. -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Sat Sep 24 03:59:26 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Sat, 24 Sep 2016 11:59:26 +0300 Subject: [Nek5000-users] =?utf-8?q?Pn-Pn_and_IFSTRS?= Message-ID: Hi Neks, in the older version of the code when trying to set up Pn-Pn and IFSTRS the code returns "Stress formulation in Pn-Pn is not supported". Trying the channel flow with the new version, I do not get this line, however, NaN values appear in the solver output. Could you please help me out? Vlad Novosibirsk State University -------------- next part -------------- An HTML attachment was scrubbed... URL: From nek5000-users at lists.mcs.anl.gov Tue Sep 27 11:10:03 2016 From: nek5000-users at lists.mcs.anl.gov (nek5000-users at lists.mcs.anl.gov) Date: Tue, 27 Sep 2016 12:10:03 -0400 Subject: [Nek5000-users] Problem reading binary .fld files into Postnek Message-ID: Hello everyone, I am having some problem importing my bineary type data into postnek. When the files are imported, seems like many elements are missing and the error message that appears in the terminal is as follows - >>MAX_WINDOWW/H! -*-Helvetica-Medium-R-Normal--*-*-*-*-*-*-*-* NEKTON Version 2.6 Enter Session Name Beginning Session g40cond_as renaming SESSION.NAME SESSION.NAME~ Session name: g40cond_as >> LTRUNC: string: 28 >>LTRUNC: string: 80 >>this is iffmat: F -1.0000000 >>WARNING: Could not open file. >> ** ERROR ** Can't open file g40cond_as.his The same files can be read correctly by Visit though. Thanks for your help. Saikat. Saikat Mukherjee, Graduate Student, Engineering Science and Mechanics, BEAM, Virginia Tech. -------------- next part -------------- An HTML attachment was scrubbed... URL: