Convergence problem in Fluent

Eduardo

Hello All I am running my a "compressible flow" case in Fluent. The solver is axisymmetry, 2D, unsteady, 2ddp, Density Base. The solver starts working at the time step = 1e-07 and it requires 5 iterations. After 30000 iterations I change the time step to 1e-06 and then after 500 iterations or so it stops converging even after increasing the courant number to 10, 100 or 1000. The solution does not blow though. Does any one have any suggestion on how to step up or look for the possible causes that can generate this problem. It is impossible to run the code all the way to 8 sec at the time step size of 1e-07, is it? Kind regards Eduardo