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August 12, 2012, 21:00 |
pisoFoam basics...
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#1 |
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David Gaden
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Location: Winnipeg, Canada
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Hello Foamers,
How do we know what time step or mesh density to use with pisoFoam? I know this should be introductory CFD basics, but it escapes me. The pisoFoam tutorial, for instance... it is currently set to deltaT = 0.005. If I re-run the simulation with the time step 1/10 the size (deltaT = 0.0005), the results are different. The pressure field differs by 15% and phi differs by 8%. Any insights would be much appreciated. -Dave
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August 13, 2012, 02:51 |
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#2 |
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Anton Kidess
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I don't think there's a simple answer to that. There are a priori error estimates (e.g. http://www.ams.org/journals/mcom/199...18-96-00701-6/), but their use is limited. In most cases, people have a posteriori error estimates, such as rerunning with a smaller timestep or higher mesh resolution, and then estimating the error e.g. with GCI or Richardson extrapolation. Jasak's thesis also might be a good read.
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August 13, 2012, 18:32 |
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#3 |
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David Gaden
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Thanks. So it is just plain old trial and error, then. Man, CFD is littered with it.
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August 16, 2012, 20:52 |
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#4 |
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Tarak
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Hii,
Do you have any idea about what the Mean/Max Courant Number (hence specifying the time step accordingly) should be for getting meaningful results with pisoFoam? |
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August 16, 2012, 20:56 |
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#5 |
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David Gaden
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If this is regarding the problem I was facing, the max was very small... around 10e-6. If this is a general question, then no, that's partly what I wanted to know.
-Dave
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August 17, 2012, 12:41 |
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#6 |
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Tarak
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That was just a general question I was curious about.
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