Abstract: In this paper, a zonal vortex method and its application to simulatingthe impulsively started flow of a circular cylinder are presented. This method treats the attached viscous flow region and the separated flow region separately- These two regions have length scales of O(Re-1/2) and O(1) respectively. The attached flow region is computed through solving boundary layer equations by finite difference method, which is fast and does not take large computer storage. Only the separated flow is computed by vortex...