# compressibility-NavierStokesEqutations in buoyantFOAM?

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 June 18, 2009, 12:04 compressibility-NavierStokesEqutations in buoyantFOAM? #1 New Member   Join Date: May 2009 Posts: 21 Rep Power: 8 hi everybody! i' ve got a quick question about the equations of buoyantFoam, i realize that most buoyant flows can be treated incompressible.. I understand that I technically solve compressible Navier Stokes equations, however i am slightly confused about the pressure correction procedure with pdyn. is this just a way of introducing a sort of artificial compressibility and when this equation is solved put back into the momentum equation (->correct)? I solve for rho, U, h and pdyn (and turb. properties) in that order. So the pressure correction term has an effect in the next time step for U.Eqn & h.Eqn? many thanxx for your help!!:-) thomas

 June 19, 2009, 09:46 #2 New Member   Yi Wang Join Date: Mar 2009 Posts: 17 Rep Power: 8 The effect of pressure correction is the same as in incompressible flow: enforce continuity.

 June 20, 2009, 05:15 #3 New Member   Join Date: May 2009 Posts: 21 Rep Power: 8 thanks for your reply! so i understand I solve the NavStokEquations in the compressible state (if UEqn would contain p_total, UEqn. would be the same form as e.g. in sonicFOAM) and that the pressure correction acts on just the dynamic pressure (not total) to enforce continuity but still for the compressible system the only thing that still confuses me is that basically all buoyant flows CFD I have seen so far was run incompressible maybe I still make a mistake in understanding the solver thanks thomas

 June 20, 2009, 07:45 #4 New Member   Yi Wang Join Date: Mar 2009 Posts: 17 Rep Power: 8 Pressure is dicomposed as: P = PRef + Pd + rho * g * h PRef is a constant, dpRef/dx =0, so it does not show up in momentum equation. -dp/dx = - dpd/dx - grad(rho)*g*h - rho*grad(rho*h) The last term is canceled out with rho*g term in the momentum equation. What you are really solving is compressible equation with gravity term in the momentum equation. Hope it helps.

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