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Checkerboarding with interFoam

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Old   July 14, 2015, 08:59
Default Checkerboarding with interFoam
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Dr. Fabian Schlegel
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Dear Foamers,

I have a very annoying problem concerning boundary conditions in multiphase flows. I like to simulate a single twodimensional bubble with interFoam. Boundary conditions are zero velocity condition at top and buttom and slip condition at the left and right wall. Alpha has zeroGradient everywhere and p_rgh fixedFluxPressure.

To generate an appropriate start solution I turned of gravity and gave the simulation some time to generate a steady solution, assuming that the bubble does not move due to missing gravity. However, after a couple of seconds my simulation crashes. The reason seems to be some oscillations (checkerboarding) visible in the horizontal velocity U at the left or right wall (velocity_slip.png). The pressure field looks strange as well (not symmetric, pressue_slip.png). I do not have a clue what is the reason for that. If I change slip to fixedValue everything is fine (velocity_fixedValue.png and pressure_fixedValue.png). I attached a testcase, if somebody wants to try it. I appreciate every help.

Best regards,
Fabian
Attached Images
File Type: jpg pressure_fixedValue.jpg (27.0 KB, 20 views)
File Type: jpg pressure_slip.jpg (30.3 KB, 21 views)
File Type: jpg velocity_fixedValue.jpg (29.2 KB, 21 views)
File Type: jpg velocity_slip.jpg (33.2 KB, 20 views)
Attached Files
File Type: zip testcase.zip (6.6 KB, 1 views)
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Old   July 15, 2015, 07:19
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Dr. Fabian Schlegel
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Heureka, the solution is written in Ferziger, Computational Methods for Fluid Dynamics, 2008 on page 294 (section 8.8) and is related to the rhie-chow correction to avoid the checkerboarding on staggered grids. There is a minimum criteria for the Courant number of Co>0.01 and I missed it.
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