On the velocity profile of inclined jets in a boundary layer for vorticity production

Abstract

The velocity profiles of air-jet vortex generators have been investigated, and the effect of varying velocity profiles on vortex production has been assessed. In the simplest case of a jet generated by fluid effusing through a cylindrical hole drilled into a solid surface, the internal flow in the nozzle is critical to the development of jets to be used for vortex production. A series of Pitot traverses through a range of jet diameters and pitch angles has been made in order to characterize the jet development. In order to produce an axisymmetric jet profile, modifications were made to the jet nozzles, thereby overcoming the critical flow features within the jet nozzle. In order to assess the jets for vortex production, a range of air-jet vortex generator configurations have been used to produce discrete vortices in a turbulent flat plate boundary layer. Velocity vectors were measured over a cross-stream plane through the vortices, from which the vorticity could be derived across the plane. The vorticity at the centre of the vortex (or the peak vorticity) was then used as an indication of the strength of the vortices. It has been shown that the nature of the jet velocity profile is not significant to the strength of the vortex, so long as the average jet velocity is held constant.