HELP TIME STEP!!

merry

Hello

I am computing an unsteady flow around an obstacle in fluent 6.1. First, I made computations with the steady case. And then when the solution converged I turn on the unsteady case.

I calculated the time step ( time step = T/100= 1.e-3 s) from the strouhal number that gives the shedding frequency (f= 1/T)of the vortex.

The problem, when I started the computations with this time step the solution converged after the 1st iteration. So, I increased the time step (1.e-2) but still the solution is converging after the 1st iteration. and then I increased the time step again and again and again.... every time the solution is converging after the 1st iteration. So, I really don't know what fluent is doing ???? it seems that for any time step the solution is converging.

Can someone explain what is really happening???

thanks

Merry