prob at high inlet velocities

nkc

Hi:

I am working on a 3D NS solver using SIMPLE method. Could anyone please advise on the following:-

(1) For a typical backward-facing step problem, the solution converges well at relatively low inlet velocities. However, at high inlet velocity (say 5-10 m/s; Re = 3000), the code just cant take it and diverges.. can anyone please explain why this happens? Anyone experienced this before?

(2) Regarding the coefficients (ap) built for the momentum equations, some authors claimed that they are indeed the same for the 3 momentum equations.. Is that absolutely true, particularly at the cell near to the wall, when the shear forces are applied only to the velocity components parallel to the wall?

Thank you.