CFL Number

For the fully spectral formulation and Cartesian co-ordinates, the CFL number is defined as

(6.6)   

where c_x , c_y , c_s and c_q is the is the propagation velocity of a wave group in the four-dimensional phase space x, y, s and q. Dx and Dy are characteristic length scale in the x- and y-direction for an element, Ds and Dq is discrete interval in the direction and frequency space and Dt is the time step interval.