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Technically Nek solves convection-diffusion (CD).
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<div>CD with nu=0 is invalid because it's a singular perturbation --- the number of</div>
<div>boundary conditions is different for the 1st-order convection eqn than for the</div>
<div>2nd-order CD equation, so Nek checks to make certain nu \ge 0.</div>
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<div>I usually set nu=1.e-31.... it won't show up in the calculation (assuming</div>
<div>your other quantities are O(1)).</div>
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<div>Best,</div>
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<div>Paul</div>
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<div id="divRpF802446" 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, March 08, 2015 9:17 AM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> Re: [Nek5000-users] Linear Advection Equation<br>
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<div dir="ltr">Thank You, Paul. <br>
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Why does the conductivity/diffusivity (i.e. param(08)) have to be small and non-zero positive? Can nek5k solve the linear advection equation without the discrete diffusion term?
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<div class="gmail_quote">On Sat, Feb 28, 2015 at 10:31 AM, <span dir="ltr"><<a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.gov</a>></span> wrote:<br>
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<div>Set ifflow to false and ifheat to T and ifadvc = F T F F F F...</div>
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<div>in the .rea file.</div>
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<div>Then, supply your velocity field in useric (ux, uy, uz), or, if you want time-varying velocity,</div>
<div>do so in usrchk by over-writing the velocity field arrays, vx(), vy(), and vz() at each step.</div>
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<div>Paul<br>
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<div style="direction:ltr"><font color="#000000" face="Tahoma"><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> Saturday, February 28, 2015 9:24 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] Linear Advection Equation<br>
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<div>Dear Users,<br>
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Is there a way to solve a linear advection equation in nek5k without computing the Navier-Stokes equations? I am simply interested in advecting a profile according to the following:<br>
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D(phi)/Dt = d (phi) /dt + v<b>.</b>grad(phi)= 0<br>
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where v<b>.</b>grad(phi) = u.d(phi)/dx + v.d(phi)/dy + w.d(phi)/dz<br>
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<div>and v is a prescribed velocity (for example v = (1,1) in 2D) <br>
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<div>Best,<br>
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<div>Saumil <br clear="all">
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-- <br>
<div class="gmail_signature">
<div dir="ltr">Saumil S. Patel<br>
Ph.D. Candidate<br>
Department of Mechanical Engineerin<font>g<br>
<a href="https://sites.google.com/site/leeccny/" dir="ltr" target="_blank">Computational Multiphase Fluid Dynamics Group</a></font><br>
The City College of New York<br>
Telephone: <a value="+12126507134">1 (212) 650-7134</a></div>
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