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October 19, 2012, 10:35 |
Time step independence?
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#1 |
Senior Member
David Gaden
Join Date: Apr 2009
Location: Winnipeg, Canada
Posts: 437
Rep Power: 21 |
Basic stuff here.
I cannot get consistent results from pisoFoam. I have a simple cavity with a cross flow inlet / outlet. I vary the time step from 0.001 to 0.0000001 s and the resulting pressure fields vary by 20-60%. Does anyone have any ideas? So far I've observed:
Yeah, I'm an OpenFOAM developer... not a user. -Dave
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October 20, 2012, 22:54 |
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#2 |
Senior Member
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Hi David,
are you comparing averaged pressure or just pressure at some time ? Regards, Awais |
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October 22, 2012, 07:49 |
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#3 |
Senior Member
Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 621
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Dave,
Are you sure that there is convergence between all of your fields at each timestep? If not, then this will have a big affect on your pressure field. Adding outer-correction will ensure convergence at each timestep. Have you looked at using pimpleFoam instead of pisoFoam? This is suggested on http://www.cfd-online.com/Forums/ope...ependency.html Last edited by chegdan; October 22, 2012 at 08:01. Reason: edit: bad grammar |
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November 5, 2012, 23:50 |
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#4 |
Senior Member
David Gaden
Join Date: Apr 2009
Location: Winnipeg, Canada
Posts: 437
Rep Power: 21 |
@Awais
I am calculating an RMS error across the entire pressure field. Average pressure doesn't vary nearly as much. @Dan Thanks for the suggestions, I will try implementing pimpleFoam into the solver. I've attached some pictures of the pressure and flow field. I'm getting a pressure fluctuation at the inlet, and discontinuities at the corners. I'm sure this is a rookie problem, but it mystifies me. These images are for velocity driven flow. When I do pressure driven flow, though, it smooths out, but I still can't get timestep independence. Thank you all for your suggestions. I will continue troubleshooting this between my full-time job and parenthood! -Dave
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