Time step independence?
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.
are you comparing averaged pressure or just pressure at some time ?
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
I am calculating an RMS error across the entire pressure field. Average pressure doesn't vary nearly as much.
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!
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