[Nek5000-users] Courant number for passive scalar

nek5000-users at lists.mcs.anl.gov nek5000-users at lists.mcs.anl.gov
Thu Jun 15 03:38:03 CDT 2017 

How does the blow-up manifest itself?

Try to run it with 2nd order in time and keep the CFL<0.5. This should be stable assuming there is no source term introducing an additional time step constraint.

Does your mesh resolve these steep gradients? 

Cheers,
Stefan
 
-----Original message-----
> From:nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
> Sent: Thursday 15th June 2017 9:29
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] Courant number for passive scalar
> 
> I havent seen the equivalent of a Courant criterion for passive scalars. 
> what I meant is the scalar is intermittent, so one should have a way to detect the regions where gradients are extremely large (fronts) and make sure to decrease the timestep there.
> <br class="" />fronts do not correspond to regions where velocities are especially large, so the classic courant criterion will miss them. 
> <br class="" />does this make sense ?
> any suggestions ?
> <br class="" />agnese
> <br class="" /><br class="" /><br class="" />On Jun 14, 2017, at 2:39 PM, nek5000-users-request at lists.mcs.anl.gov <mailto:nek5000-users-request at lists.mcs.anl.gov> wrote:
> <br class="Apple-interchange-newline" />Send Nek5000-users mailing list submissions to<br class="" />	nek5000-users at lists.mcs.anl.gov <mailto:nek5000-users at lists.mcs.anl.gov><br class="" /><br class="" />To subscribe or unsubscribe via the World Wide Web, visit<br class="" />	https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users<br class="" />or, via email, send a message with subject or body 'help' to<br class="" />	nek5000-users-request at lists.mcs.anl.gov<br class="" /><br class="" />You can reach the person managing the list at<br class="" />	nek5000-users-owner at lists.mcs.anl.gov<br class="" /><br class="" />When replying, please edit your Subject line so it is more specific<br class="" />than "Re: Contents of Nek5000-users digest..."<br class="" />Today's Topics:<br class="" /><br class="" />   1. Re: Courant for passive scalar ? (nek5000-users at lists.mcs.anl.gov)<br class="" />   2. Re: Courant for passiv
 e scalar
  ? (nek5000-users at lists.mcs.anl.gov)<br class="" /><br class="" />From: nek5000-users at lists.mcs.anl.gov<br class="" />Subject: Re: [Nek5000-users] Courant for passive scalar ?<br class="" />Date: June 14, 2017 at 10:44:13 AM GMT+2<br class="" />To: nek5000-users at lists.mcs.anl.gov<br class="" />Reply-To: nek5000-users at lists.mcs.anl.gov<br class="" /><br class="" /><br class="" />Thanks Jan !
> <br class="" />so it is confirmed that the tilmestep is based exclusively on the velocity field ?
> how do people make sure that the passive scalars do not blow up ? 
> anybody ?
> <br class="" />any help is greatly appreciated !!
> agnese
> <br class="" /><br class="" />Agnese Seminara
> --------------------------------
> CNRS
> Institut de Physique de Nice
> Parc Valrose 
> avenue J Vallot
> 06108 Nice, France
> +33 (0) 492 076 775
> http://sites.unice.fr/site/aseminara/ <http://sites.unice.fr/site/aseminara/><br class="" />On Jun 13, 2017, at 7:00 PM, nek5000-users-request at lists.mcs.anl.gov <mailto:nek5000-users-request at lists.mcs.anl.gov> wrote:
> <br class="Apple-interchange-newline" />Send Nek5000-users mailing list submissions to<br class="" />	nek5000-users at lists.mcs.anl.gov <mailto:nek5000-users at lists.mcs.anl.gov><br class="" /><br class="" />To subscribe or unsubscribe via the World Wide Web, visit<br class="" />	https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users<br class="" />or, via email, send a message with subject or body 'help' to<br class="" />	nek5000-users-request at lists.mcs.anl.gov<br class="" /><br class="" />You can reach the person managing the list at<br class="" />	nek5000-users-owner at lists.mcs.anl.gov<br class="" /><br class="" />When replying, please edit your Subject line so it is more specific<br class="" />than "Re: Contents of Nek5000-users digest..."<br class="" />Today's Topics:<br class="" /><br class="" />   1. Re: Courant for passive scalar ? (nek5000-users at lists.mcs.anl.gov)<br class="" />   2. prenek (nek5000-users@
 lists.mc
 s.anl.gov)<br class="" /><br class="" />From: nek5000-users at lists.mcs.anl.gov<br class="" />Subject: Re: [Nek5000-users] Courant for passive scalar ?<br class="" />Date: June 12, 2017 at 8:00:26 PM GMT+2<br class="" />To: nek5000-users at lists.mcs.anl.gov<br class="" />Reply-To: nek5000-users at lists.mcs.anl.gov<br class="" /><br class="" /><br class="" />Hi,
> I haven' t tried this myself, but I guess you could write a subroutine that calculates the maximum timestep from the scalar field and sets dt accordingly. Then simple call the routine from userchk.
> <br class="" />Best,
> Jan
> <br class="" />Am 12.06.2017 um 18:15 schrieb nek5000-users at lists.mcs.anl.gov <mailto:nek5000-users at lists.mcs.anl.gov>:<br class="" /><br class="" />Dear Neks
> <br class="" />I am running a simulation of a channel, with a passive scalar. Using diffusivity=viscosity, the velocity field converges nicely, whereas the passive scalar blows up at some random point down the simulation. Reynolds number is 10 000 so its in the turbulent regime.
> <br class="" />I suspect this is due to the fact that the passive scalar is intermittent, so sometimes large fluctuations will occur, totally uncorrelated to velocity fluctuations. to avoid the code to blow up, one would need to setup the timestep based on a courant criterion for the scalar, and not for the velocity. 
> <br class="" />has this already been implemented ?
> or how do people avoid this ?
> <br class="" />any suggestion is more than welcome.
> thanks
> Agnese
> <br class="" /><br class="" /><br class="" />Agnese Seminara
> --------------------------------
> CNRS
> Institut de Physique de Nice
> Parc Valrose 
> avenue J Vallot
> 06108 Nice, France
> +33 (0) 492 076 775
> http://sites.unice.fr/site/aseminara/ <http://sites.unice.fr/site/aseminara/><br class="" />_______________________________________________<br class="" />Nek5000-users mailing list<br class="" />Nek5000-users at lists.mcs.anl.gov <mailto:Nek5000-users at lists.mcs.anl.gov><br class="" />https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users <https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users><br class="" /><br class="" /><br class="" /><br class="" />From: nek5000-users at lists.mcs.anl.gov<br class="" />Subject: [Nek5000-users] prenek<br class="" />Date: June 13, 2017 at 12:12:49 PM GMT+2<br class="" />To: nek5000-users at lists.mcs.anl.gov<br class="" />Reply-To: nek5000-users at lists.mcs.anl.gov<br class="" /><br class="" /><br class="" />Hi nek,
> <br class="" />I have a 2D mesh. When I used global refine function, the errors occurred. do you know why?
> <br class="" /> OCT/Multi-SPLIT
> quad or multi-split? (q/m)
> Number of elements after OctSplit operation:    7680
> Are you sure you want to split (y/n)?
>  inside gencen         7680 F           4
>  done gencen         7680
>  start locglob_lexico:           4        7680       30720   2.00000009E-03
>  locglob:           1           1       30720
>  locglob:           2        3664       30720
>  locglob:           1        7761       30720
>  locglob:           2        7761       30720
>  Performing unique_vertex2 self_chk       30720
>  done locglob_lexico:      7761      7761     30720         4
>  Performing makecell self_chk       30720
> <br class="" />  RMIN: 0.153545E-03
>   EPS,RMIN: 0.500000E-01 0.153545E-03
>  I/O Error: No String Terminator sent to PRS
>  zeroing y:     1  82 -0.75715434E-10
>  I/O Error: No String Terminator sent to PRS
>  zeroing y:     4  82 -0.14778734E-11
>  I/O Error: No String Terminator sent to PRS
>  zeroing y:     4  83  0.72759583E-10
>  I/O Error: No String Terminator sent to PRS
>  zeroing y:     4 123  0.15279482E-09
> ......
> <br class="" />Does it mean my mesh is still not right?
> <br class="" /><br class="" />_______________________________________________<br class="" />Nek5000-users mailing list<br class="" />Nek5000-users at lists.mcs.anl.gov<br class="" />https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users<br class="" /><br class="" /><br class="" /><br class="" /><br class="" />From: nek5000-users at lists.mcs.anl.gov<br class="" />Subject: Re: [Nek5000-users] Courant for passive scalar ?<br class="" />Date: June 14, 2017 at 2:37:35 PM GMT+2<br class="" />To: nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov><br class="" />Reply-To: nek5000-users at lists.mcs.anl.gov<br class="" /><br class="" /><br class="" />How do you define a courant number for a scalar?<br class="" /><br class="" />-----Original message-----<br class="" />From:nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov><br class="" />Sent: Wednesday 14th June 2017 10:43<br class="" />To: nek5000-users at lists.mcs
 .anl.gov
 <br class="" />Subject: Re: [Nek5000-users] Courant for passive scalar ?<br class="" /><br class="" />Thanks Jan !<br class="" /><br class="" />so it is confirmed that the tilmestep is based exclusively on the velocity field ?<br class="" />how do people make sure that the passive scalars do not blow up ? <br class="" />anybody ?<br class="" /><br class="" />any help is greatly appreciated !!<br class="" />agnese<br class="" /><br class="" /><br class="" />Agnese Seminara<br class="" />--------------------------------<br class="" />CNRS<br class="" />Institut de Physique de Nice<br class="" />Parc Valrose <br class="" />avenue J Vallot<br class="" />06108 Nice, France<br class="" />+33 (0) 492 076 775<br class="" />http://sites.unice.fr/site/aseminara/ <http://sites.unice.fr/site/aseminara/><br class="" />On Jun 13, 2017, at 7:00 PM, nek5000-users-request at lists.mcs.anl.gov <mailto:nek5000-users-request at lists.mcs.a
 nl.gov> 
 wrote:<br class="" /><br class="Apple-interchange-newline" />Send Nek5000-users mailing list submissions to<br class="" />	nek5000-users at lists.mcs.anl.gov <mailto:nek5000-users at lists.mcs.anl.gov><br class="" /><br class="" />To subscribe or unsubscribe via the World Wide Web, visit<br class="" />	https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users<br class="" />or, via email, send a message with subject or body 'help' to<br class="" />	nek5000-users-request at lists.mcs.anl.gov<br class="" /><br class="" />You can reach the person managing the list at<br class="" />	nek5000-users-owner at lists.mcs.anl.gov<br class="" /><br class="" />When replying, please edit your Subject line so it is more specific<br class="" />than "Re: Contents of Nek5000-users digest..."<br class="" />Today's Topics:<br class="" /><br class="" />   1. Re: Courant for passive scalar ? (nek5000-users at lists.mcs.anl.gov)<br class="" />   2. 
 prenek (
 nek5000-users@<br class="" /> lists.mc<br class="" /> s.anl.gov)<br class="" /><br class="" />From: nek5000-users at lists.mcs.anl.gov<br class="" />Subject: Re: [Nek5000-users] Courant for passive scalar ?<br class="" />Date: June 12, 2017 at 8:00:26 PM GMT+2<br class="" />To: nek5000-users at lists.mcs.anl.gov<br class="" />Reply-To: nek5000-users at lists.mcs.anl.gov<br class="" /><br class="" /><br class="" />Hi,<br class="" />I haven' t tried this myself, but I guess you could write a subroutine that calculates the maximum timestep from the scalar field and sets dt accordingly. Then simple call the routine from userchk.<br class="" /><br class="" />Best,<br class="" />Jan<br class="" /><br class="" />Am 12.06.2017 um 18:15 schrieb nek5000-users at lists.mcs.anl.gov <mailto:nek5000-users at lists.mcs.anl.gov>:<br class="" /><br class="" />Dear Neks<br class="" /><br class="" />I am running a simulation of a channel, with a passive scalar. Usi
 ng diffu
 sivity=viscosity, the velocity field converges nicely, whereas the passive scalar blows up at some random point down the simulation. Reynolds number is 10 000 so its in the turbulent regime.<br class="" /><br class="" />I suspect this is due to the fact that the passive scalar is intermittent, so sometimes large fluctuations will occur, totally uncorrelated to velocity fluctuations. to avoid the code to blow up, one would need to setup the timestep based on a courant criterion for the scalar, and not for the velocity. <br class="" /><br class="" />has this already been implemented ?<br class="" />or how do people avoid this ?<br class="" /><br class="" />any suggestion is more than welcome.<br class="" />thanks<br class="" />Agnese<br class="" /><br class="" /><br class="" /><br class="" />Agnese Seminara<br class="" />--------------------------------<br class="" />CNRS<br class="" />Institut de Physique de Nice<br class="" />Parc
  Valrose
  <br class="" />avenue J Vallot<br class="" />06108 Nice, France<br class="" />+33 (0) 492 076 775<br class="" />http://sites.unice.fr/site/aseminara/ <http://sites.unice.fr/site/aseminara/><br class="" />_______________________________________________<br class="" />Nek5000-users mailing list<br class="" />Nek5000-users at lists.mcs.anl.gov <mailto:Nek5000-users at lists.mcs.anl.gov><br class="" />https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users <https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users><br class="" /><br class="" /><br class="" /><br class="" />From: nek5000-users at lists.mcs.anl.gov<br class="" />Subject: [Nek5000-users] prenek<br class="" />Date: June 13, 2017 at 12:12:49 PM GMT+2<br class="" />To: nek5000-users at lists.mcs.anl.gov<br class="" />Reply-To: nek5000-users at lists.mcs.anl.gov<br class="" /><br class="" /><br class="" />Hi nek,<br class="" /><br class="" />I have a 2D mesh. When I used global refine fu
 nction, 
 the errors occurred. do you know why?<br class="" /><br class="" /> OCT/Multi-SPLIT<br class="" />quad or multi-split? (q/m)<br class="" />Number of elements after OctSplit operation:    7680<br class="" />Are you sure you want to split (y/n)?<br class="" /> inside gencen         7680 F           4<br class="" /> done gencen         7680<br class="" /> start locglob_lexico:           4        7680       30720   2.00000009E-03<br class="" /> locglob:           1           1       30720<br class="" /> locglob:           2        3664       30720<br class="" /> locglob:           1        7761      A0 30720
 <br class="" /> locglob:           2        7761       30720<br class="" /> Performing unique_vertex2 self_chk       30720<br class="" /> done locglob_lexico:      7761      7761     30720         4<br class="" /> Performing makecell self_chk       30720<br class="" /><br class="" />  RMIN: 0.153545E-03<br class="" />  EPS,RMIN: 0.500000E-01 0.153545E-03<br class="" /> I/O Error: No String Terminator sent to PRS<br class="" /> zeroing y:     1  82 -0.75715434E-10<br class="" /> I/O Error: No String Terminator sent to PRS<br class="" /> zeroing y:     4  82 -0.14778734E-11<br class="" /> I/O Error: No String Terminator sent to PRS<br class="" /> zeroing y:     4  83  0.72759583E-10<br class=""
  />Â=A
 0I/O Error: No String Terminator sent to PRS<br class="" /> zeroing y:     4 123  0.15279482E-09<br class="" />......<br class="" /><br class="" />Does it mean my mesh is still not right?<br class="" /><br class="" /><br class="" />_______________________________________________<br class="" />Nek5000-users mailing list<br class="" />Nek5000-users at lists.mcs.anl.gov<br class="" />https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users<br class="" /><br class="" />_______________________________________________<br class="" />Nek5000-users mailing list<br class="" />Nek5000-users at lists.mcs.anl.gov<br class="" />https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users<br class="" /><br class="" /><br class="" /><br class="" />_______________________________________________<br class="" />Nek5000-users mailing list<br class="" />Nek5000-users at lists.mcs.anl.gov<br class="" />https://lists.mcs.anl.gov/mailman/listinfo
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