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<span style="font-size: 11pt;">Hi Klaus,</span></div>
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<span style="margin: 0px; font-size: 11pt">Thank you so much for your reply. </span></div>
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<span style="margin: 0px; font-size: 11pt">Does this work for a multi-fluid problem as well? Can i specify separate viscosities to each of the materials?</span></div>
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<span style="margin: 0px; font-size: 11pt">Best,</span></div>
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<span style="margin: 0px; font-size: 11pt">Nitish</span></div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Klaus Weide <klaus@flash.uchicago.edu><br>
<b>Sent:</b> Thursday, June 18, 2020 12:36 PM<br>
<b>To:</b> Acharya, Nitish <nachary2@ur.rochester.edu><br>
<b>Cc:</b> flash-users@flash.uchicago.edu <flash-users@flash.uchicago.edu><br>
<b>Subject:</b> [EXTERNAL] Re: [FLASH-USERS] Adding viscous term in the momentum equation</font>
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<div class="PlainText">On Fri, 12 Jun 2020, Acharya, Nitish wrote:<br>
<br>
> I figured FLASH solves only the non-viscous Euler equations for <br>
> simulating HED experiments. I plan to solve a complete Navier Stokes <br>
> Equation for a Laserslab problem by explicitly defining a constant <br>
> viscosity coefficient for materials. From what I understand, I might <br>
> have to add a viscous term in the momentum equation and modify the hydro <br>
> unit in FLASH. How convenient is it to implement this? What should be <br>
> the general approach to add this extra term in the hydro solver? I would <br>
> really appreciate any sort of help here?<br>
<br>
As Rodrigo Fernandez already pointed out, you can use the "flux-based" <br>
part of the "Diffuse" unit for your purpose. You will need to include<br>
<br>
physics/Diffuse/DiffuseFluxBased<br>
<br>
in your configuration, as well as an implementation of the Viscosity unit, <br>
and set appropriate runtime parameters. Hopefully the User's Guide can <br>
help you further.<br>
<br>
Keep in mind that this is an explicit implementation; FLASH currently does <br>
not provide an implicit (or semi-implicit) solver for viscosity. So your <br>
time step may have to become significantly smaller than what you are used <br>
to.<br>
<br>
Klaus<br>
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