<html dir="ltr">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css" style="">
<!--
p
{margin-top:0;
margin-bottom:0}
-->
</style><style id="owaParaStyle" type="text/css">P {margin-top:0;margin-bottom:0;}</style>
</head>
<body ocsi="0" fpstyle="1" dir="ltr">
<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Hi Friedrich,<br>
<br>
There are some alternatives to the nozzle (turb_outflow) outflow boundary condition, alternatives on which we work right now<br>
a) stabilized outflow boundary condition (Dong et al. 2014)<br>
b) convective boundary conditions<br>
<br>
These have been tested on simple 2d cases but not on full turbulence. Let us know if you are willing to try and test them for your case and we can send the files.<br>
<br>
Oana<br>
<br>
<div style="font-family: Times New Roman; color: #000000; font-size: 16px">
<hr tabindex="-1">
<div style="direction: ltr;" id="divRpF72070"><font color="#000000" face="Tahoma" size="2"><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, April 05, 2015 4:49 AM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> [Nek5000-users] turbflow_outflow() - emergency<br>
</font><br>
</div>
<div></div>
<div>
<div id="divtagdefaultwrapper" style="font-size:12pt; color:#000000; background-color:#FFFFFF; font-family:Calibri,Arial,Helvetica,sans-serif">
<p>Dear all,</p>
<p><br>
</p>
<p>I am using Nek5000 to do DNS of jet flow.</p>
<p><br>
</p>
<p>As my turbulent flow reaches the end of the domain the CFL number increases rapidly and thus the simulation crashes.</p>
<p><br>
</p>
<p>My understanding of this issue is that it is caused by a turbulent backflow, thus one should try to accelerate the flow a little in this region to prevent this from occurring.</p>
<p><br>
</p>
<p>After trying to reduce dt and divergence parameter I included the subroutine accl_outflow() as described in the expansion example. This was unsuccessful, thus I also tried to implement the turb_outflow() subroutine which again did not solve my problem.</p>
<p><br>
</p>
<p>I am unsure how to proceed, the only way forward that I can tell is to make a variable timestep.</p>
<p><br>
</p>
<p>I look forward to hearing your responses,</p>
Friedrich
<p><br>
</p>
</div>
</div>
</div>
</div>
</body>
</html>