Convergence problems in CFX5

Soren

Hi, all

I have some problems with the convergence in CFX5.

The problem is about ventialtion of a large atrium with many small inlets and outlets. Ratio between size of inlets heigth compared to Atrium heigth is 1:250. At the inlet the velocity are giving and at the outlets opening is applied. The total number of elements is about 600.000. Upwind in used for advection schemes. RNG-k-eps is used. Buoyancy is applied. In the beginning I use small physical timestep in order to get the solution process going (0.1s). The advection time scale is 5.1. But after 30-50 iteration the solution process suddenly divergence (FINMEM).

I have no idea what could be the problem. Lower the physical time the solution process takes forever.

Could anyone give me an idea of what could be the solution to this problem.

Regards

Soren