Pressure and Three-Component Velocity Measurements on a Diffuser That Generates Longitudinal Vortices

This paper presents flowfield measurements on a wide-angle, three-dimensional diffuser that has a vastly improved static-pressure recovery over the corresponding plane-wall diffuser when discharging into a plenum. The diffuser geometry consists of a pyramid-shaped insert attached to the diffuser expansion wall. The upsweep on the upper surface of the pyramid generates a transverse pressure gradient that causes the incoming flow to roll up into two symmetric, longitudinal vortices. Earlier flow-visualization studies have shown that these vortices replace the closed separated regions along the diffuser expansion wall, eliminating flow oscillations and hysteresis. This paper presents quantitative information, in the form of static pressure, total pressure, and three-component Laser Doppler Velocimeter (LDV) measurements, on the diffuser flowfield for two variations in the pyramid geometry. Information from these studies is useful in developing configurations with enhanced pressure recoveries. The greatly improved static-pressure recovery of this diffuser, combined with its superior flowfield features, make it particularly suitable for exhaust diffuser applications.