hello please tell me what is the importance of courant number in CFD. thanks a lot

The solution will generally converge faster for larger Courant numbers, unless the integration scheme becomes unstable. Since you have performed some initial iterations, and the solution is stable, you can try increasing the Courant number to speed up convergence. If the residuals increase without bound, or you get a floating point exception, you will need to decrease the Courant number, read in the previous data file, and try again.

The solution will generally converge faster for larger Courant numbers, unless the integration scheme becomes unstable. Since you have performed some initial iterations, and the solution is stable, you can try increasing the Courant number to speed up convergence. If the residuals increase without bound, or you get a floating point exception, you will need to decrease the Courant number, read in the previous data file, and try again.