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Old   August 12, 2012, 21:00
Default pisoFoam basics...
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David Gaden
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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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Old   August 13, 2012, 02:51
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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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Old   August 13, 2012, 18:32
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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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Old   August 16, 2012, 20:52
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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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Old   August 16, 2012, 20:56
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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.

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Old   August 17, 2012, 12:41
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That was just a general question I was curious about.
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