how to calculate CFL number in 3D convection-diffusion channel flow
1. 3D channel flow , equation is
df/dt + c df/dx = nu*d^2f/dx^2
unsteady channel flow
2. spacial discretization is second CDS, time discretization is implicit Euler.
3. in x,y,z direction, length of FVM is dx,dy,dz respectively,
how to calculate CFL number in 3D case?
in peric's book , it was mentioned :
dt < 1/(2*nu/dx**2 + c/dx)
but it was 1D case, in channel flow, x direction is convective dorminated,
while in y direction(normal to wall), grid is fine, diffusion may be important.
welcome any reply
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