# New pressure and velocity boundary condition derived from the mixedFvPatchField.C

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June 14, 2014, 05:01
New pressure and velocity boundary condition derived from the mixedFvPatchField.C
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zhanglei
Join Date: May 2013
Location: China
Posts: 19
Rep Power: 6
Hello, everyone
The attachment is my pressure BC(filterPA) and velocity BC(filterUA) derived from the mixed BC.Just like the inletoutlet BC, the both of the new BC finish defining the valueFraction().The valueFraction() of my BC is defined according to the alpha.
The different between filterPA and filterUA is when the valueFraction() of pressure(or velocity) BC is equal to 1, the valueFraction() of velocity(or pressure) BC is equal to 0. On one hand, when the prssure BC is the dirichlet type, the velocity BC is the Neumann type. The pressure on the patch with a fixedvalue(eg. 1e5) and the velocity on the same patch with a zerogradient can form a "outlet" on this patch.On the other hand, when the prssure BC is the Neumann type, the velocity BC is the dirichlet type. The pressure on the patch with a zerogradient and the velocity on the same patch with a fixedvalue(eg.(0 0 0)) can form a "no-slip BC" on this patch.
In the 0/p_rgh, the BC is defined like:
wall
{
type filterPA;
value uniform 1e5;
wallValue uniform 1e5;
}
In the 0/U, the BC is defined like:
wall
{
type filterUA;
value uniform (0 0 0);
wallValue uniform (0 0 0);
}
Maybe the train of thought of this two BC is a mistake or the somewhere of the code is wrong, I got a strange result shown as the picture which shows the velocity field near the patch when the patch is "outlet".
I donot know how to solve, any answer is welcome! thanks!
Attached Images
 u.jpg (72.2 KB, 10 views) ux.jpg (55.0 KB, 7 views) uy.jpg (87.0 KB, 7 views)
Attached Files
 myBCs-zhanglei.tar.gz (9.4 KB, 3 views)

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