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Hi Andrew,
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<div>In my view, you are already getting the correct flow physics.</div>
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<div>What happens at outflow, especially at moderate Reynolds number, is not</div>
<div>necessarily parallel flow.</div>
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<div>The stress formulation is giving the stress-free result.</div>
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<div>Paul</div>
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<div id="divRpF999418" style="direction: ltr;"><font face="Tahoma" size="2" color="#000000"><b>From:</b> nek5000-users-bounces@lists.mcs.anl.gov [nek5000-users-bounces@lists.mcs.anl.gov] on behalf of nek5000-users@lists.mcs.anl.gov [nek5000-users@lists.mcs.anl.gov]<br>
<b>Sent:</b> Sunday, December 13, 2015 5:19 PM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> Re: [Nek5000-users] Stress formulation<br>
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<div>Hi Paul, <br>
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Thank you for your reply. </div>
<div>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.
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Can you recommend me what kind of boundary conditions i can utilise for ensure for ensure the flow physics<font color="#000000" face="tahoma, arial, verdana, sans-serif, Lucida Sans"><span style="font-size:11px; line-height:16.5px"> ?</span></font> I would
implement these one in code. <br>
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Thanks,<br>
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Andrew<br>
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<div class="gmail_quote">2015-12-05 3:37 GMT+01:00 <span dir="ltr"><<a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.gov</a>></span>:<br>
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Hi Andrew,
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<div>I checked into this... I think what is happening is that the 'O ' bc for the stress formulation</div>
<div>means stress-free, which is not guaranteed to yield a parabolic profile at the outlet.</div>
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<div>If you increase your Reynolds number I'm guessing that you'll recover the parabolic</div>
<div>profile because the viscous stresses will diminish -- this is what I observed.</div>
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<div>From my perspective, the outlet boundary is not a region where I would count on accurate</div>
<div>physics --- it is, after all, a truncated domain, so I don't generally worry too much about</div>
<div>the behavior there.</div>
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<div>Paul</div>
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<div style="direction:ltr"><font face="Tahoma" size="2" color="#000000"><b>From:</b>
<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov" target="_blank">nek5000-users-bounces@lists.mcs.anl.gov</a> [<a href="mailto:nek5000-users-bounces@lists.mcs.anl.gov" target="_blank">nek5000-users-bounces@lists.mcs.anl.gov</a>] on behalf of
<a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.gov</a> [<a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.gov</a>]<br>
<b>Sent:</b> Tuesday, December 01, 2015 2:44 AM<br>
<b>To:</b> <a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.gov</a><br>
<b>Subject:</b> [Nek5000-users] Stress formulation<br>
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<div><span lang="en"><span title="Andrew"></span></span>Hi Neks,<br>
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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>
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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>
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Thanks in advance for your help,<br>
Best regards,<br>
Andrew<br>
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