<div dir="ltr">Hi Ricardo,<div>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.</div><div><br></div><div>Cheers</div><div>Rif</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sun, Dec 13, 2015 at 11:39 PM, <span dir="ltr"><<a href="mailto:nek5000-users-request@lists.mcs.anl.gov" target="_blank">nek5000-users-request@lists.mcs.anl.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Send Nek5000-users mailing list submissions to<br>
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Today's Topics:<br>
<br>
1. Re: Stress formulation (<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>)<br>
2. Re: Stress formulation (<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>)<br>
3. freestream turbulence at INLET (<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>)<br>
4. Re: freestream turbulence at INLET<br>
(<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>)<br>
<br>
<br>
----------------------------------------------------------------------<br>
<br>
Message: 1<br>
Date: Mon, 14 Dec 2015 00:19:30 +0100<br>
From: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
Subject: Re: [Nek5000-users] Stress formulation<br>
Message-ID:<br>
<<a href="mailto:mailman.11996.1450048795.24727.nek5000-users@lists.mcs.anl.gov">mailman.11996.1450048795.24727.nek5000-users@lists.mcs.anl.gov</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
Hi Paul,<br>
<br>
Thank you for your reply.<br>
Yes, if i increase Reynolds number, the outlet profile become much close to<br>
the inlet one. But in my simulations the Reynolds number is between 300 and<br>
1200.<br>
Can you recommend me what kind of boundary conditions i can utilise for<br>
ensure for ensure the flow physics ? I would implement these one in code.<br>
<br>
Thanks,<br>
Andrew<br>
<br>
<br>
2015-12-05 3:37 GMT+01:00 <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>>:<br>
<br>
><br>
> Hi Andrew,<br>
><br>
> I checked into this... I think what is happening is that the 'O ' bc for<br>
> the stress formulation<br>
> means stress-free, which is not guaranteed to yield a parabolic profile<br>
> at the outlet.<br>
><br>
> If you increase your Reynolds number I'm guessing that you'll recover the<br>
> parabolic<br>
> profile because the viscous stresses will diminish -- this is what I<br>
> observed.<br>
><br>
> From my perspective, the outlet boundary is not a region where I would<br>
> count on accurate<br>
> physics --- it is, after all, a truncated domain, so I don't generally<br>
> worry too much about<br>
> the behavior there.<br>
><br>
> Paul<br>
><br>
> ------------------------------<br>
> *From:* <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.mcs.anl.gov</a> [<br>
> <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.mcs.anl.gov</a>] on behalf of<br>
> <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>]<br>
> *Sent:* Tuesday, December 01, 2015 2:44 AM<br>
> *To:* <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
> *Subject:* [Nek5000-users] Stress formulation<br>
><br>
> Hi Neks,<br>
><br>
> I have one question about stress formulation in NEK5000.<br>
> I tried to make a simulation for Poiseuil flow with stress<br>
> formulation. In inlet boundary condition use was made of parabolic profile.<br>
> If IFSTRS=false the outlet profile is exactly the same as inlet one but in<br>
> case of IFSTRS=true the outlet profile changes significantly (both the<br>
> maximum value and profile shape). Could you tell me how I can get the<br>
> parabolic profile at outlet, please?<br>
> The same thing occurs with pressure values. The maximum pressure<br>
> value with IFSTRS=true is three times higher then the one with IFSTRS=false.<br>
><br>
> I found that the difference comes from subroutines where the<br>
> stiffness matrix is calculated (axehlm for IFSTRS = false and axhmsf for<br>
> IFSTRS = true) but I don't undestand what is happening exactly.<br>
><br>
> Thanks in advance for your help,<br>
> Best regards,<br>
> Andrew<br>
><br>
> _______________________________________________<br>
> Nek5000-users mailing list<br>
> <a href="mailto:Nek5000-users@lists.mcs.anl.gov">Nek5000-users@lists.mcs.anl.gov</a><br>
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Message: 2<br>
Date: Sun, 13 Dec 2015 23:55:04 +0000<br>
From: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
To: "<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>"<br>
<<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>><br>
Subject: Re: [Nek5000-users] Stress formulation<br>
Message-ID:<br>
<<a href="mailto:mailman.11997.1450050923.24727.nek5000-users@lists.mcs.anl.gov">mailman.11997.1450050923.24727.nek5000-users@lists.mcs.anl.gov</a>><br>
Content-Type: text/plain; charset="iso-8859-1"<br>
<br>
<br>
Hi Andrew,<br>
<br>
In my view, you are already getting the correct flow physics.<br>
<br>
What happens at outflow, especially at moderate Reynolds number, is not<br>
necessarily parallel flow.<br>
<br>
The stress formulation is giving the stress-free result.<br>
<br>
Paul<br>
<br>
<br>
<br>
________________________________<br>
From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.mcs.anl.gov</a>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>]<br>
Sent: Sunday, December 13, 2015 5:19 PM<br>
To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
Subject: Re: [Nek5000-users] Stress formulation<br>
<br>
Hi Paul,<br>
<br>
Thank you for your reply.<br>
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.<br>
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.<br>
<br>
Thanks,<br>
Andrew<br>
<br>
<br>
2015-12-05 3:37 GMT+01:00 <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><mailto:<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>>>:<br>
<br>
Hi Andrew,<br>
<br>
I checked into this... I think what is happening is that the 'O ' bc for the stress formulation<br>
means stress-free, which is not guaranteed to yield a parabolic profile at the outlet.<br>
<br>
If you increase your Reynolds number I'm guessing that you'll recover the parabolic<br>
profile because the viscous stresses will diminish -- this is what I observed.<br>
<br>
>From my perspective, the outlet boundary is not a region where I would count on accurate<br>
physics --- it is, after all, a truncated domain, so I don't generally worry too much about<br>
the behavior there.<br>
<br>
Paul<br>
<br>
________________________________<br>
From: <a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.mcs.anl.gov</a><mailto:<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.mcs.anl.gov</a>> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.mcs.anl.gov</a><mailto:<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov">nek5000-users-bounces@lists.mcs.anl.gov</a>>] on behalf of <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><mailto:<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>> [<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><mailto:<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>>]<br>
Sent: Tuesday, December 01, 2015 2:44 AM<br>
To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><mailto:<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>><br>
Subject: [Nek5000-users] Stress formulation<br>
<br>
Hi Neks,<br>
<br>
I have one question about stress formulation in NEK5000.<br>
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?<br>
The same thing occurs with pressure values. The maximum pressure value with IFSTRS=true is three times higher then the one with IFSTRS=false.<br>
<br>
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.<br>
<br>
Thanks in advance for your help,<br>
Best regards,<br>
Andrew<br>
<br>
_______________________________________________<br>
Nek5000-users mailing list<br>
<a href="mailto:Nek5000-users@lists.mcs.anl.gov">Nek5000-users@lists.mcs.anl.gov</a><mailto:<a href="mailto:Nek5000-users@lists.mcs.anl.gov">Nek5000-users@lists.mcs.anl.gov</a>><br>
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<br>
Message: 3<br>
Date: Mon, 14 Dec 2015 11:48:09 +0800<br>
From: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
To: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
Subject: [Nek5000-users] freestream turbulence at INLET<br>
Message-ID:<br>
<<a href="mailto:mailman.12001.1450064910.24727.nek5000-users@lists.mcs.anl.gov">mailman.12001.1450064910.24727.nek5000-users@lists.mcs.anl.gov</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
Hi neks,<br>
I looked at this nek5000 simulation on youtube of a flow over an airfoil.<br>
<a href="https://www.youtube.com/watch?v=aR-hehP1pTk" rel="noreferrer" target="_blank">https://www.youtube.com/watch?v=aR-hehP1pTk</a><br>
In the video, a Dirichlet condition was imposed at the inlet from a RANS<br>
simulation. My question is how do you this?<br>
I have a RANS simulation from Fluent which prescribes freestream<br>
turbulence. I wish to use a plane of the Fluent simulations as my inlet in<br>
the nek solver. Can you help with this?<br>
<br>
Cheers<br>
Rif<br>
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Message: 4<br>
Date: Mon, 14 Dec 2015 07:39:19 +0100<br>
From: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
To: "<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>"<br>
<<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>><br>
Subject: Re: [Nek5000-users] freestream turbulence at INLET<br>
Message-ID:<br>
<<a href="mailto:mailman.12007.1450075185.24727.nek5000-users@lists.mcs.anl.gov">mailman.12007.1450075185.24727.nek5000-users@lists.mcs.anl.gov</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
Dear Rif,<br>
<br>
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.<br>
<br>
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?<br>
<br>
Best regards,<br>
<br>
Ricardo Vinuesa.<br>
<br>
Sent from Mail for Windows 10<br>
<br>
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</blockquote></div><br></div>