Abstract: A conduit for carrying fluid in a downstream direction includes a diffusing section. Downstream extending convolutions in the wall of a diffusing section energize the boundary layer and delay boundary layer separation from the wall surface of the diffusing section or permit an increase in the diffusion angle without the occurrence of separation. Such convolutions are particularly useful when rapid diffusion is required in a short distance, such as in the diffusing section of automotive catalytic converter systems. Such a system carries engine exhaust products from a small, cylindrical pipe into a typically larger elliptical cross-section catalyst filled portion. The convolutions help to more uniformly disperse the exhaust gas throughout the catalyst bed using a relatively short diffusion section.

Abstract: To reduce noise, an automotive exhaust tailpipe has a convoluted surface at or near its outlet to generate pairs of counterrotating axial vortices within the exhaust gases just before or just as the gases exit the tailpipe. The convoluted surface may be the internal surface of the tailpipe, or a thin-walled convoluted member may be disposed within the tailpipe near its outlet end.

Abstract: A thin, convoluted wall member disposed upstream of the inlet of a diffuser generates large-scale vortices having axes in the downstream direction. The vortices enhance mixing within the diffuser and can also energize the boundary layer, thereby improving diffuser performance and delaying the onset of stall. Greater diffusion angles without stall are possible. The member itself creates low losses.