The Influence of Shear Layer Turbulence on Stationary Pseudoblades in Supersonic Pressure Exchange Inducing Flow Fields

Abstract

The pressure exchange process can be initiated by nonsteady pressure forces that arise due to moving fluid dynamic interfaces in the laboratory frame of reference. The fluid interfaces are flow features of “pseudoblades” that can be generated by an expanding supersonic primary flow, impinging on freely spinning cone-vane type of rotors. These pseudoblades are fluidic vanes that interface with an entrained, compressible secondary fluid and can mimic the action of impellers as in conventional turbomachinery. The overarching goal of this research is the development of a novel fluid impeller-based ejector. The authors’ motivation towards this study was in understanding the boundary conditions leading to spatial deterioration of pseudoblades. Flow around stationary, axisymmetrically aligned rotors (the ramp vane and double cone type), held in a primary supersonic flow field (Mach 1.44 jet), were investigated by laser Doppler velocimetry (LDV) measurements of shear layer turbulence intensity (TI) under alternative seeding of primary and entrained secondary flows. Rotors were tested and compared for shear layer TI distribution-based boundary conditions, anticipated pseudoblade conditions and an “effective persistence length of stationary pseudoblades.” The results suggest that the double cone rotor is most conducive for pseudoblade stability. The TI distribution-based boundary conditions for this rotor indicate that the effective pseudoblade persistence length approximately equals the exit diameter of the supersonic nozzle.