Hi, How do I determine the CFL number for an explicit hypersonic problem? Is there any book or paper?

Thanks, Subramani

CFL number (Courant-Friedrich-Levy). For discretized transport problems, the CFL number determines how many mesh cells, a fluid element passes during a time step. Or rather, the fraction of a time step to pass one cell. For compressible flow, the definition is different. Here, the CFL number determines how many cells are passed by a propagating perturbation. Hence, the wave-speed, i.e. fluid speed plus the sound speed, is employed. For explicit time stepping schemes, such as Runge-Kutta, the CFL number must be less than the stability limit for the actual scheme to converge. For implicit and semi-implicit schemes, the CFL limit does not constitute a stability limit. On the other hand, the range of parameters in which these schemes converge may often be characterized by the CFL number.

Alfonso Medina, OpenFlower Manual

Good Lick

Thanks a lot. I am running a steady state problem in FLUENT. Say, my Mach number is 2 and temperature is 227.81 K and grid spacing of 1e-6 m then dt=dx/(a*(M+1))=1.1e-9 This is my dt and do I need to multiply this by a factor of 0.9 to get the CFL number?

Thanks, Subramani