about Courant number
 

Hello all.

I'm studying the cavity flow.
I was running the cavity case, I faced with a very strange problem.

After the cavity steady solution fully converged, I changed it to unsteady simulation.
Unsteady Reynolds averaged Navier-Stokes equations were used to simulate cavity flow with a time-step of Δt=10-5 s.

I have measured static pressure oscillations at the cavity centre to obtain St number.

When I set the courant number at 3, there is no pressure oscillations at the critical point inside cavity along with time. :confused:
(Residuals remain under 10-3)
When I set the courant number at 4, pressure oscillations can be observed at the same point along with time.
But I can't find high peak in SPL-frequency plot. :eek:
(Residuals remain under 10-2)

Other conditions were completely same, only changed courant number.
I can't get any reasonable results until now. How can i change my CFD schemes to obtain better results? What is the problem?

Thanks in advance!