Zonal vortex method and impulsively started flow around a circular cylinder

IN this paper, a zonal vortex method and its application to simulating the impulsively started flow of a circular cylinder are presented. This method treats the attached viscous flow region and the separated flow region separately. The attached flow region is computed through solving boundarylayer equations by the finite-difference method. Only the separated flow is computed through solving Navier-Stokes equations by the vortex method. Since the separated flow region has a length scale of 0(1), in the vortex method used for this region, the number of new vortices introduced at the surface of the body per time step is relatively insensitive to the Reynolds number of the flow. For simulation of high- Reynolds-number flows with massive separation, the total number of vortices in the flowfield, hence the computer storage and computer time, is greatly reduced.