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 gerardosrez July 9, 2012 10:11

pressure boundary conditions

Hi cfd colleagues,

What are the pressure boundary conditions I have to set for the following boundaries?:

1) Flow entering through a boundary.
2) Flow exiting through a boundary (corrected mass flow).
3) Wall with no slip condition.

For (3) I use isolated boundary for pressure equation (no diffusion through boundary), but I'm not sure what do I have to use for (1) and (2) because I'm confuse if I have to set 0 value for pressure nodes at the exit (let's say a pipe or duct exit) or is it a no diffusion boundary condition on pressure equation.

This is a collocated variable CVFEM scheme on triangular grids...

Best regards...

 juliom July 9, 2012 10:30

Dear Gerardo.
In your first question, you may use dinamic pressure.
In your second question, I would use 0, because I assume your are using "outflow" as a result, you will have the other pressure, from an explicit way.
At any wall the pressure you selecte is the same as you define as a pressure reference!
Greetings !!!! from INELMECA!!

 FMDenaro July 9, 2012 11:46

Quote:
 Originally Posted by gerardosrez (Post 370462) Hi cfd colleagues, What are the pressure boundary conditions I have to set for the following boundaries?: 1) Flow entering through a boundary. 2) Flow exiting through a boundary (corrected mass flow). 3) Wall with no slip condition. For (3) I use isolated boundary for pressure equation (no diffusion through boundary), but I'm not sure what do I have to use for (1) and (2) because I'm confuse if I have to set 0 value for pressure nodes at the exit (let's say a pipe or duct exit) or is it a no diffusion boundary condition on pressure equation. This is a collocated variable CVFEM scheme on triangular grids... Best regards...

depends on your case ... are you solving compressible of incompressible flow? The mathematical problem is different ...

 gerardosrez July 9, 2012 18:17

Quote:
 Originally Posted by FMDenaro (Post 370487) depends on your case ... are you solving compressible of incompressible flow? The mathematical problem is different ...
Hi FMDENARO, right now I´m solving incompressible flow but I´m interested in compressible flow too because this solver will be improved for solving the shallow water equations so I need both advises ;)..

Thanks in advance FMDENARO...

 FMDenaro July 10, 2012 03:41

this paper can give useful suggestions

Poinsot T. et Lele S. (1992). Boundary conditions for direct simulations of compressible reacting flows. Journal of Computational Physics. 101, 1, 104-129.

otherwise, for incompressible flows, when the pressure equation is derived from the continuity constraint (divergence-free velocity field), the boundary conditions for the pressure are derived from the Hodge decomposition

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