Bc for velocity splitting
 

Dear all,

I would like to compute an incompressible turb. jet by LES and after that splitting the velocity field u = {u_1, u_2, u_3} into a potential and rotating part:

u = rot psi + grad phi

after applying the div - operator on this equ., I end up with

div u = 0 = laplace phi

Can anybody say how to find some usefull bc for this problem. Outside the jet flow I have u = 0 and also phi = 0, but at the jet outflow and inflow, I can not say phi = 0, otherwise I had the trivial solution ( with homogenous dirichlet at the bc) phi =0 everywhere which is obviously wrong. Has anybody experience in this matter or can refer some literature.

thanks in advance Matthias