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buoyantPimpleFoam high velocity values

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Old   March 26, 2015, 06:26
Default buoyantPimpleFoam high velocity values
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Luuk Buijs
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Dear Foamers,

I'm trying to implement variable density and viscosity in buoyantPimpleFoam (bPF) for a simple Rayleigh-Benard problem in a cubical cavity. My simulations are working fine for buoyantBoussinesqPimpleFoam (bBPF), but switching to bPF causes some problems. See my previous thread for a more detailed explanation.

I've tried changing the standard hotRoom tutorial for bPF to my own problem step by step, and I've run into something that surprises me. Running the standard hotRoom without a temperature gradient, generates physically significant (~20cm/s) velocity values. This seems very strange to me, because I don't see any other forcing active. Running the exact same tutorial in bBPF results in a nice 0 velocity field, as I would expect. Trying to trace back why this is happening looking at the UEqn-file in bPF, I figured this is coming from the values of p_rgh, which are quite large. I don't have a physical explanation for this though. Can anybody tell me what is happening?

Just for clarity: this is the completely standard hotRoom tutorial, copied from the bPF folder in OF.

Many thanks!
Luuk
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Old   March 30, 2015, 05:14
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Any ideas anyone?
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Old   April 9, 2015, 09:41
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Hi Luuk,

it could be more or less the same problem with pressure initialisation already described here:
http://www.cfd-online.com/Forums/ope...tml#post460410
With the Boussinesq approximation p_rgh is independent of the height otherwise it is not anf it is assumed constant over height on boundary conditions you obtain a flow.

Hannes
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