The problem of obtaining proper flow spreading together with useful pressure recovery across rapidly expanding diffusers is of considerable practical importance. Many different approaches to this end have been reported in literature, e.g. vortex generators, screens or baffles, surface roughness, corrugations, etc., apart from the use of direct boundary-layer control. These methods have the common aim of preventing separation from the walls of the diffuser. With increasing expansion angle and area-ratio, however, the effectiveness of these methods either breaks down or is obtained at a high cost of pressure recovery.