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Gravity source term in PisoFoam

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Old   November 28, 2012, 13:59
Default Gravity source term in PisoFoam
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Dan M
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I have a question regarding adding a source term to the momentum equation in the piso solver. I would like to model a channel flow taking into account the effect of gravity. To do so I have adjusted the solver as follows:

fvVectorMatrix UEqn
+ fvm::div(phi, U)
+ turbulence->divDevReff(U)
- gravity

I have specified a non uniform pressure outlet condition to the channel that takes into account the effect of gravity. When solving the problem I attain a pressure distribution that seem reasonable (hydrostatic pressure distribution). However, I experience oscillations of the vertical velocity component (U1). This is seen in the attached picture that shows the velocity distribution across the channel height. The picture corresponds to the beginning of the simulation where the horizontal velocity is still zero and the vertical velocity should also be equal to zero across the height. It seems like the boundaries are causing some issues. I have used standard no slip conditions for U and zeroGradient for p so I am not sure what is causing the error. Is there something else I need to consider when trying to include gravity in a pisoFoam flow?

I would greatly appreciate any help.

Thank you very much,

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