<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I remember looking at variable density flow equations long time ago in the context of R. T. instability<div>and what I recall is that the governing equations are pretty much the same as the low Mach ones w/o source terms</div><div>see for example ( <span class="Apple-style-span" style="color: rgb(51, 102, 153); font-weight: bold; font-size: large; ">The mixing transition in Rayleigh–Taylor instability </span><a href="http://journals.cambridge.org/action/displayJournal?jid=FLM" title="Journal of Fluid Mechanics">Journal of Fluid Mechanics</a> /
Volume 511 /
July 2004,
pp 333-362)</div><div>you will need to have two passive scalars in addition to the mass and momentum equations.</div><div><br></div><div>Ammar</div><div><br></div><div><br></div><div><br></div><div><div><div>On Oct 11, 2013, at 11:54 AM, <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr"><div style="">Hi Paul</div><div style=""><br></div>For variable density case do I need to use the low mach number version or some other way ?<div><br></div><div style="">Thanks</div><div style="">praveen</div></div><div class="gmail_extra">
<br><br><div class="gmail_quote">On Fri, Oct 11, 2013 at 8:24 PM, <span dir="ltr"><<a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
In principle, this should work with the Pn-Pn-2 STRESS formulation, but<br>
I don't think it has been thoroughly tested.<br>
<br>
Regarding large viscosity variations, work needs to be done on the<br>
preconditioners for the viscous terms. This hasn't been a traditional<br>
focus for Nek5000, which has been aimed at high Reynolds number flows<br>
where the viscous solves are essentially trivial (compared to the<br>
pressure, say).<br>
<br>
Certainly, there are things that could be done to be effective in<br>
this space. I would start by running some test problems with the<br>
STRESS formulation to see if you get the accuracy you're after. If<br>
so, then we can look into performance enhancement via better preconditioning<br>
strategies for the case at hand.<br>
<br>
HTH,<br>
<br>
Paul<br>
<div><div class="h5"><br>
----- Original Message -----<br>
From: <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
To: "nek5000" <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>><br>
Sent: Friday, October 11, 2013 9:16:24 AM<br>
Subject: [Nek5000-users] Fwd: Variable density flows<br>
<br>
<br>
<br>
Hello<br>
<br>
<br>
<br>
<br>
<br>
Can we solve variable density incompressible flows with nek5000 ? For e.g. see the model given by eq. 2.1 here<br>
<br>
<br>
<a href="http://www.math.tamu.edu/~guermond/PUBLICATIONS/guermond_quartapelle_JCP_2000.pdf" target="_blank">http://www.math.tamu.edu/~guermond/PUBLICATIONS/guermond_quartapelle_JCP_2000.pdf</a><br>
<br>
<br>
<br>
Also, can nek handle variable viscosity with large variations ?<br>
<br>
<br>
Thanks<br>
praveen<br>
<br>
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