Abstract: The viscous flow around a rectangular cylinder is simulated by solving the two dimensional compressible Navier-Stokes equations. The partial differential equations are approximated by difference methods such as special chosen Jacobian matrix splitting technique and approximate factorization. The scheme has second order accuracy in space and time. The Mach number Ma =0.3 and the Reynold number Re = 20000 are used in the computation. The unsteady Karman vortex separation and asymmetry of pair of vortices can be seen clearly from the computed results, The old vortices are moved downstream and the new ones are generated from the corner of the cylinder. The influence of compressibility on vortex formation is considered. The critical Reynold number Rec is increased with the Mach number increased.

Key words: Blunt bodies, separated flow, N-S equation, numerical calculation