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Combining BCs: wall - outlet. Boundary layer disappears

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Old   July 20, 2009, 18:12
Post Combining BCs: wall - outlet. Boundary layer disappears
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Martina Friedrich
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Dear Foamers,

I've got a question: combining the boundary conditions wall - outlet.

For the cells between the two boundary conditions (with one face wall and another outlet BC) I would expect that the boundary condition (velocity = uniform (0 0 0)) yields also in the last cell!
I've tested several solver (ico, turb, rasCavitating, interPhaseChange - Foam) and the wall-boundary condition is always ignored. (see attached file in the next thread)

I expect a boundary layer till the outlet. But one cell in front of the outlet, the boundary layer disappears. Does anyone know why this effect exists?

My idea is: a velocity near zero at an outlet can perhaps lead to negative velocities at the outlet and therefore the boundary type can change from outlet to opening. There for numerical arguments leads to this effect. Am I right?

Thanks
Martina

Last edited by MartinaF; July 20, 2009 at 18:42.
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Old   July 20, 2009, 18:14
Default image of the effect
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Martina Friedrich
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The picture shows the velocity field of my simulation case: wall (blue color) and outlet (circle, multicolored).
The upper case is from rasCavitatingFoam and the lower case from CFX.
You can also see the grid I used and that the effect I explained takes place in the last cells.
Attached Images
File Type: jpg cell_wall_outlet.jpg (84.6 KB, 13 views)
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