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<p style="margin-top:0;margin-bottom:0">Hi Ali,</p>
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<p style="margin-top:0;margin-bottom:0">Two questions:</p>
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<p style="margin-top:0;margin-bottom:0">1) How are you forcing your flow? (Do you have periodic boundary conditions in x ? Are you using constant flow rate?</p>
<p style="margin-top:0;margin-bottom:0">(p54 = -1; p55=1 would be recommended for periodic bcs </p>
<p style="margin-top:0;margin-bottom:0">with ffx=0 in the .usr file).</p>
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<p style="margin-top:0;margin-bottom:0">2) If your Reynolds number is Re = Ubar H / nu , where </p>
<p style="margin-top:0;margin-bottom:0">H=channel half height and </p>
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<p style="margin-top:0;margin-bottom:0"> Re > (2/3) * 5772</p>
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<p style="margin-top:0;margin-bottom:0">then you should find that you have sustained unsteadiness.</p>
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<p style="margin-top:0;margin-bottom:0">That is, you should have linear instabilities that will grow and saturate to some truly nonlinear (unsteady) state.</p>
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<p style="margin-top:0;margin-bottom:0">[ The 2/3 is because Re=5772 is the transition point for 2D plane channel flow based on U_max, when the background profile is </p>
<p style="margin-top:0;margin-bottom:0">U=(1-y*y)*Umax and H=1. In this case, Ubar = 2/3 * Umax .]</p>
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<p style="margin-top:0;margin-bottom:0">In general, you won't have turbulence in 2D.</p>
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<p style="margin-top:0;margin-bottom:0">hth,</p>
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<p style="margin-top:0;margin-bottom:0">Paul</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Nek5000-users <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> Friday, March 9, 2018 11:21:46 AM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> [Nek5000-users] Small random perturbations</font>
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<div>Dear Dr.Fischer,</div>
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<div>Actually, I am doing 2-D simulation, at least for now, so no z-dimension is up there. Am I wrong to do DNS in 2-D? Also, I just started doing so, and I think my files are not useful at this point. </div>
<div>Let me try more, maybe I am missing something. </div>
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<div>Thank you for your awesome free code and your continuous support.</div>
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<div>Ali </div>
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<div><a href="https://lists.mcs.anl.gov/pipermail/nek5000-users/2018-March/005133.html" class="x_OWAAutoLink" id="LPlnk323673">https://lists.mcs.anl.gov/pipermail/nek5000-users/2018-March/005133.html</a><br>
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