<div dir="ltr"><div><div>Hi Paul, <br><br></div>No, I have run my own example with my grid, but now I'm running "axi" case in examples and after 20000 steps I don't get the parabolic profile.<span lang="en"><span> In addition,</span> <span>the solution</span> <span>does not change</span> <span>after 1000</span> <span>steps.</span></span><span></span></div><div><br></div>Best, Andrew<br></div><div class="gmail_extra"><br><div class="gmail_quote">2015-12-18 17:19 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><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt"><span class="">
<div><br>
</div>
<div><br>
</div>
Hi Andrew
<div><br>
</div>
<div>Are you running the "axi" case in the examples?</div>
<div><br>
</div>
<div>This case started with u=0 as an initial condition.</div>
<div><br>
</div>
<div>A quick glance at the output it produces in f00004, after 200 steps, shows plots</div>
<div>similar to yours.</div>
<div><br>
</div>
<div>If you run longer (change nsteps in the .rea file), the viscous boundary layer</div>
<div>will diffuse inward from the walls and you should see a parabolic profile. This</div>
<div>is what I observed just now.</div>
<div><br>
</div>
<div>Please let me know if this resolves the issue --- if not, I'm happy to check</div>
<div>further.</div>
<div><br>
</div>
</span><div>Best, Paul</div>
<div><br>
</div>
<div style="font-family:Times New Roman;color:#000000;font-size:16px">
<hr>
<div style="direction:ltr"><font color="#000000" face="Tahoma" size="2"><span class=""><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>
</span><b>Sent:</b> Thursday, December 17, 2015 7:07 PM<div><div class="h5"><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> Re: [Nek5000-users] Stress formulation<br>
</div></div></font><br>
</div><div><div class="h5">
<div></div>
<div>
<div dir="ltr"><span lang="en"><span>Hi Paul, <br>
</span></span>
<div><span lang="en"><span><br>
I think I have</span> <span>misspoken</span><span>.</span> <span>The thing is</span>
<span>that I</span> <span>haven't got</span> <span>the profile</span> <span>corresponding to the</span>
<span>inlet one</span> <span></span><span>anywhere</span> <span>in pipe</span><span></span><span>.</span>
<span></span><span><br>
</span><span>I</span> <span>add some</span> <span>clarifications.</span> <span>You can</span>
<span>find attached</span> <span>file with</span> <span>velocity</span> <span>curves</span>
<span>for my</span> <span>simulaltions</span><span>.</span> <br>
<span>I have done the</span> <span>simulations of</span> <span>Poiseuille flow</span>
<span>in the cylindrical</span> <span>pipe.</span> <span>With</span> <span></span><span>IFAXIS</span>
<span>= true</span><span>,</span> <span>IFSTRS</span> <span>= false</span><span>,</span>
<span>param</span> <span>(30) = 0</span> <span>the</span> <span>input</span> <span>
profile doesn't chage.</span> <span>With</span> <span></span><span>IFAXIS</span> <span>
= true</span><span>,</span> <span>IFSTSR</span> <span>= true</span><span>,</span>
<span>param (</span><span>30)</span> <span>=</span> <span>0 </span><span>the</span>
<span>input velocity profile changes</span> <span>considerably along the pipe</span> <span>and</span>
<span>on the axis</span> <span>there is strange</span> <span>pressure peak</span><span>,</span>
<span>the nature</span> <span>of which I</span> <span>can not understand</span><span>.</span> Can
<span>I</span> <span>have</span> <span>clarification on</span> <span>this </span>
<span>question?<br>
<br>
</span></span></div>
<div><span lang="en"><span>Thanks, <br>
</span></span></div>
<div><span lang="en"><span>Andrew<br>
</span></span></div>
<div><br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2015-12-14 0:55 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>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">
<div><br>
</div>
Hi Andrew,
<div><br>
</div>
<div>In my view, you are already getting the correct flow physics.</div>
<div><br>
</div>
<div>What happens at outflow, especially at moderate Reynolds number, is not</div>
<div>necessarily parallel flow.</div>
<div><br>
</div>
<div>The stress formulation is giving the stress-free result.</div>
<div><br>
</div>
<div>Paul</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
<div style="font-family:Times New Roman;color:#000000;font-size:16px">
<hr>
<div style="direction:ltr"><font color="#000000" face="Tahoma" size="2"><span><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>
</span><b>Sent:</b> Sunday, December 13, 2015 5:19 PM<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> Re: [Nek5000-users] Stress formulation<br>
</font><br>
</div>
<div>
<div>
<div></div>
<div>
<div dir="ltr">
<div>
<div>
<div>Hi Paul, <br>
<br>
</div>
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.
<br>
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>
<br>
</div>
Thanks,<br>
</div>
Andrew<br>
<div>
<div><br>
</div>
</div>
</div>
<div class="gmail_extra"><br>
<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>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">
<div><br>
</div>
Hi Andrew,
<div><br>
</div>
<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>
<div><br>
</div>
<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>
<div><br>
</div>
<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>
<div><br>
</div>
<div>Paul</div>
<div><br>
<div style="font-family:Times New Roman;color:#000000;font-size:16px">
<hr>
<div style="direction:ltr"><font color="#000000" face="Tahoma" size="2"><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>
</font><br>
</div>
<div>
<div>
<div></div>
<div>
<div dir="ltr">
<div><span lang="en"><span title="Andrew"></span></span>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>
</div>
</div>
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