Pressure boundary conditions
 

Hi all,

First I thought that if you have a boundary condition which imposes pressure only, the velocity at that point is taken as being the same as the neighbouring cell. In fact it imposes

grad(v)*n = 0

near to the pressure (outflow) boundary, but I supposed that for many flows, it's not a problem.

Now I wonder if solving the unknowns for boundary conditions would make the system a little less stiff.

The problem is: I already have 3 equations (Navier Stokes X and Y and continuity) for each cell, as well as 3 unknowns (X and Y velocities and P). I cannot solve it if I have additional unknowns for boundary conditions. The problem for boundary conditions imposing velocity only is the same.

Some people told me to read Versteeg and Malalasekera, but I didn't find exactly what I search.

Any idea ? Thanx in advance

Re: Pressure boundary conditions
 

for pressure b.c----

on the outflow---p=0 and any other plane normal gradient of p is =0

try it.