[Nek5000-users] Nek5000-users Digest, Vol 82, Issue 11

Mon Dec 14 01:08:00 CST 2015

Hi Ricardo,
I am using the k-omega SST turbulence model in Fluent to simulate a 3D flow
over the S805 airfoil. The wind tunnel measurements measured turbulence
intensity at 0.4% with wind speed of 2.8 m/s. It is a time dependent
simulation. What I plan to do is emulate the RANS inlet velocity field in
the NEK5000 DNS simulations at the inlet. Can you help with this?  Many
thanks.

Cheers
Rif

On Sun, Dec 13, 2015 at 11:39 PM, <nek5000-users-request at lists.mcs.anl.gov>
wrote:

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> Today's Topics:
>
>    1. Re: Stress formulation (nek5000-users at lists.mcs.anl.gov)
>    2. Re: Stress formulation (nek5000-users at lists.mcs.anl.gov)
>    3. freestream turbulence at INLET (nek5000-users at lists.mcs.anl.gov)
>    4. Re: freestream turbulence at INLET
>       (nek5000-users at lists.mcs.anl.gov)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 14 Dec 2015 00:19:30 +0100
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] Stress formulation
> Message-ID:
>         <mailman.11996.1450048795.24727.nek5000-users at lists.mcs.anl.gov>
> Content-Type: text/plain; charset="utf-8"
>
> Hi Paul,
>
> Thank you for your reply.
> Yes, if i increase Reynolds number, the outlet profile become much close to
> the inlet one. But in my simulations the Reynolds number is between 300 and
> 1200.
> Can you recommend me what kind of boundary conditions i can utilise for
> ensure for ensure the flow physics ? I would implement these one in code.
>
> Thanks,
> Andrew
>
>
> 2015-12-05 3:37 GMT+01:00 <nek5000-users at lists.mcs.anl.gov>:
>
> >
> > Hi Andrew,
> >
> > I checked into this... I think what is happening is that the 'O  ' bc for
> > the stress formulation
> > means stress-free, which is not guaranteed to yield  a parabolic profile
> > at the outlet.
> >
> > If you increase your Reynolds number I'm guessing that you'll recover the
> > parabolic
> > profile because the viscous stresses will diminish -- this is what I
> > observed.
> >
> > From my perspective, the outlet boundary is not a region where I would
> > count on accurate
> > physics --- it is, after all, a truncated domain, so I don't generally
> > worry too much about
> > the behavior there.
> >
> > 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, December 01, 2015 2:44 AM
> > *To:* nek5000-users at lists.mcs.anl.gov
> > *Subject:* [Nek5000-users] Stress formulation
> >
> > Hi Neks,
> >
> >     I have one question about stress formulation in NEK5000.
> >     I tried to make a simulation for Poiseuil flow with stress
> > formulation. In inlet boundary condition use was made of parabolic
> profile.
> > If IFSTRS=false the outlet profile is exactly the same as inlet one but
> in
> > case of IFSTRS=true the outlet profile changes significantly (both the
> > maximum value and profile shape). Could you tell me how I can get the
> > parabolic profile at outlet, please?
> >      The same thing occurs with pressure values. The maximum pressure
> > value with IFSTRS=true is three times higher then the one with
> IFSTRS=false.
> >
> >      I found that the difference comes from subroutines where the
> > stiffness matrix is calculated (axehlm for IFSTRS = false and axhmsf for
> > IFSTRS = true) but I don't undestand what is happening exactly.
> >
> > Thanks in advance for your help,
> > Best regards,
> > Andrew
> >
> > _______________________________________________
> > Nek5000-users mailing list
> > Nek5000-users at lists.mcs.anl.gov
> > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> >
> >
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> ------------------------------
>
> Message: 2
> Date: Sun, 13 Dec 2015 23:55:04 +0000
> From: nek5000-users at lists.mcs.anl.gov
> To: "nek5000-users at lists.mcs.anl.gov"
>         <nek5000-users at lists.mcs.anl.gov>
> Subject: Re: [Nek5000-users] Stress formulation
> Message-ID:
>         <mailman.11997.1450050923.24727.nek5000-users at lists.mcs.anl.gov>
> Content-Type: text/plain; charset="iso-8859-1"
>
>
> Hi Andrew,
>
> In my view, you are already getting the correct flow physics.
>
> What happens at outflow, especially at moderate Reynolds number, is not
> necessarily parallel flow.
>
> The stress formulation is giving the stress-free result.
>
> 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: Sunday, December 13, 2015 5:19 PM
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] Stress formulation
>
> Hi Paul,
>
> Thank you for your reply.
> Yes, if i increase Reynolds number, the outlet profile become much close
> to the inlet one. But in my simulations the Reynolds number is between 300
> and 1200.
> Can you recommend me what kind of boundary conditions i can utilise for
> ensure for ensure the flow physics ? I would implement these one in code.
>
> Thanks,
> Andrew
>
>
> 2015-12-05 3:37 GMT+01:00 <nek5000-users at lists.mcs.anl.gov<mailto:
> nek5000-users at lists.mcs.anl.gov>>:
>
> Hi Andrew,
>
> I checked into this... I think what is happening is that the 'O  ' bc for
> the stress formulation
> means stress-free, which is not guaranteed to yield  a parabolic profile
> at the outlet.
>
> If you increase your Reynolds number I'm guessing that you'll recover the
> parabolic
> profile because the viscous stresses will diminish -- this is what I
> observed.
>
> >From my perspective, the outlet boundary is not a region where I would
> count on accurate
> physics --- it is, after all, a truncated domain, so I don't generally
> worry too much about
> the behavior there.
>
> Paul
>
> ________________________________
> From: nek5000-users-bounces at lists.mcs.anl.gov<mailto:
> nek5000-users-bounces at lists.mcs.anl.gov> [
> 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<mailto:nek5000-users at lists.mcs.anl.gov> [
> nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>]
> Sent: Tuesday, December 01, 2015 2:44 AM
> To: nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov
> >
> Subject: [Nek5000-users] Stress formulation
>
> Hi Neks,
>
>     I have one question about stress formulation in NEK5000.
>     I tried to make a simulation for Poiseuil flow with stress
> formulation. In inlet boundary condition use was made of parabolic profile.
> If IFSTRS=false the outlet profile is exactly the same as inlet one but in
> case of IFSTRS=true the outlet profile changes significantly (both the
> maximum value and profile shape). Could you tell me how I can get the
> parabolic profile at outlet, please?
>      The same thing occurs with pressure values. The maximum pressure
> value with IFSTRS=true is three times higher then the one with IFSTRS=false.
>
>      I found that the difference comes from subroutines where the
> stiffness matrix is calculated (axehlm for IFSTRS = false and axhmsf for
> IFSTRS = true) but I don't undestand what is happening exactly.
>
> Thanks in advance for your help,
> Best regards,
> Andrew
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov<mailto:Nek5000-users at lists.mcs.anl.gov>
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>
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> ------------------------------
>
> Message: 3
> Date: Mon, 14 Dec 2015 11:48:09 +0800
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Subject: [Nek5000-users] freestream turbulence at INLET
> Message-ID:
>         <mailman.12001.1450064910.24727.nek5000-users at lists.mcs.anl.gov>
> Content-Type: text/plain; charset="utf-8"
>
> Hi neks,
> I looked at this nek5000 simulation on youtube of a flow over an airfoil.
> https://www.youtube.com/watch?v=aR-hehP1pTk
> In the video, a Dirichlet condition was imposed at the inlet from a RANS
> simulation. My question is how do  you this?
> I have a RANS simulation from Fluent which prescribes freestream
> turbulence. I wish to use a plane of the Fluent simulations as my inlet in
> the nek solver. Can you help with this?
>
> Cheers
> Rif
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> ------------------------------
>
> Message: 4
> Date: Mon, 14 Dec 2015 07:39:19 +0100
> From: nek5000-users at lists.mcs.anl.gov
> To: "nek5000-users at lists.mcs.anl.gov"
>         <nek5000-users at lists.mcs.anl.gov>
> Subject: Re: [Nek5000-users] freestream turbulence at INLET
> Message-ID:
>         <mailman.12007.1450075185.24727.nek5000-users at lists.mcs.anl.gov>
> Content-Type: text/plain; charset="utf-8"
>
> Dear Rif,
>
> In our wing simulation the boundary layers are tripped using a volume
> force in the direction normal to the surface. This emulates the approach in
> wind tunnel experiments, where the models are tripped using sand paper, V
> disturbances, etc. In such wind tunnel tests the transition location is
> prescribed, and the freestream turbulence intensity is very low. The idea
> is to have a ?canonical? turbulent boundary layer, developing in the most
> controlled way in order to study the effects of turbulence. Therefore, in
> our wing simulation turbulence is also zero at our boundaries.
>
> Regarding the use of Fluent data in Nek, could you give us some more
> information about your setup? Which RANS model are you using, and is it
> time-dependent? What kind of geometry are you simulating?
>
> Best regards,
>
> Ricardo Vinuesa.
>
> Sent from Mail for Windows 10
>
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> End of Nek5000-users Digest, Vol 82, Issue 11
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