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Hi Tony,
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<div>I would just set p55=1.0; p54=-1.0</div>
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<div>This will fix < u_x > == 1.0</div>
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<div>If you are using variable viscosity, this might be problematic, but for the</div>
<div>constant viscosity case this is the best way.</div>
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<div>Be certain to also set ffx=ffy=ffz=0 in the .usr file, the the p54/p55 combination</div>
<div>sets the x-body force as needed to ensure the prescribed mass flux is realized.</div>
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<div>Paul</div>
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<div id="divRpF840581" 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, August 31, 2014 5:57 PM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> [Nek5000-users] Constant mass flow rate in simulation<br>
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<div style="margin-top:0; margin-bottom:0">Dear Neks,</div>
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<div style="margin-top:0; margin-bottom:0">Recently I've been struggling with constant mass flow rate in my turbulent channel flow simulation. Based on the userchk subroutine in 'turbChannel' tutorial case, I also used torque_calc(1.0,x0,.false.,.false.) to
calculate the wall shear and then got the mean wall shear. After that I set mean pressure gradient 'ffx' equal to the mean wall shear in order to keep constant mass flow rate. In this case, the flow rate started from 1 (nondimensionalised case, bulk mean equal
to 1) and kept increasing. Although the increment was very small at each time step, it never stopped and the bulk mean velocity has increased to 1.002.</div>
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<div style="margin-top:0; margin-bottom:0">Is it appropriate to set constant mass flow rate by updating mean pressure gradient based on mean wall shear in Nek5000 or am I using the wrong calculation? Since the bulk mean is still increasing, the simulation is
like acceleration channel flow.</div>
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<div style="margin-top:0; margin-bottom:0">Does anyone has any clue about how to set constant mass flow rate for turbulent channel flow in Nek5000? Any idea is appreciated and many thanks in advance.<br>
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<div style="margin-top:0; margin-bottom:0">Thanks and regards,<br>
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<div style="margin:0"><font face="Calibri,Arial,Helvetica,sans-serif">Tony</font></div>
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