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Inlet boundary condition - coupling local inlet velocity with local static pressure
Posted 14 déc. 2014, 09:27 UTC−5 Fluid & Heat, Computational Fluid Dynamics (CFD), Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers 0 Replies
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as already described in the linked discussion (www.comsol.com/community/forums/general/thread/54351/) I want to study the steady flow in the gap between an air-hockey table and a levitating rectangular plate with a structured surface. Because I am not interested in the flow in the plate of the air-hockey table, I have tried to substitute the flow in porous media (Darcy’s law) with an equal boundary condition at the bottom of the gap (laminar flow, Navier-Stokes equations). It makes sense to me, to couple the local inlet velocity with the local static pressure at the inlet. Far away from the lateral outlet the inlet velocity will be very low (almost or equal zero), whereas near the outlet the inlet velocity will become maximal. Hence the boundary condition at the inlet is given by the expression
Form a mathematical point of view this boundary condition seems to be correct, however Comsol has some trouble with handling it. Do you have any experience using similar boundary conditions?
Do you have any advices how to improve the speed of convergence or my model at all? Is it possible to get rid of this numerical unstable boundary condition and replace it with another equal but more stable one. I have also tried to reinterpret the inlet velocity boundary
This works perfectly in 2D, but in 3D I don’t get any solution if the aspect ratio
For those of you, who are interested in this problem, I will upload a model tomorrow.
Thank you very much in advance.
Best regards
Maximilian
PS. I know that my boundary conditions is not realistic regarding the tangential velocity at the boundary. Nevertheless I want to use it ;-) I have already ruled out problems with the mesh by assuming the inlet velocity to be constant or a function of space.
Hello mts
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