Static Pressure Inlet - Static Pressure Outlet
Hello,
My FDM code simulates Backward Facing Step flow when I use conventional BCs such as defining velocity profile at inlet and fully developed condition at outlet. I have validated the results and it seems functioning correctly. However, when I want to impose a pressure-pressure condition (both static), it only converges when a zero-gradient condition is selected for inlet. When I try to use mass balance to update inlet normal velocity at each iteration, the solution eventually blows up. I am integrating outflow and use the mean velocity as a uniform inlet velocity. Also I am interested to know if there is any difference to use momentum balance and mass balance to update inlet normal velocity. Has anyone faced this problem before? I appreciate your help:) |
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Well, you should provide more details... 1) are you using Neumann at walls and Dirichlet at inflow and outflow? what about the pressure difference ? 2) are you using staggered or colocated grid? 3) how do you discretize the pressure equation? |
Thanks Duri and Filippo for your comments. I am using a collocated explicit MacCormack (predictor-corrector) scheme for incompressible flow with pseudo-compressibility coupling for pressure. The BCs that converge for pressure-pressure are listed below:
@inlet: p=p_in , du/dx=0 , dv/dx=0 @outlet: p=p_out , du/dx=0, dv/dx=0 @walls: dp/dy=0 (or the extended version) , u=0, v=0 The BCs that won't converge: @inlet: p=p_in , u=U_in , v=0 @outlet: p=p_out , du/dx=0, dv/dx=0 @walls: dp/dy=0 (or the extended version) , u=0, v=0 I find "U_in" from mass conservation at the end of each iteration and update it. I have used pressure-pressure condition in CFX without zero-gradient condition so many times, so there should be a way for convergence. |
The error is that you can not prescribe both pressure and velocity as Dirichlet bc
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Thanks Filippo. I did not know about this. Could you kindly introduce me a book or paper that discusses what kind of Dirichlet and Neumann conditions go well together?
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https://www.researchgate.net/publica..._viscous_flows |
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compressible or incompressible???
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