Unsteady turbulence model computation
 

Hello~ everyone. I want to simulate unsteady turbulent jet flow using some turb. models. I met some strange problem. When I set time step small, solutions converged to steady state and there is no flucutation. However when I set time step large, solutions have oscillation. Why this phenonmenon happen ?? In my thought, though time step is small, it must be flow oscillation. Do you know this problem ??

Thanks in advance.

Happy new year everybody~~