Filtered Rayleigh Scattering Measurements in Helium-Air Mixing Experiments of Selected Streamwise Vortex Interactions in a Mach 2.5 Flow

Abstract

An experimental study of the mixing capabilities of a pre-selected streamwise vortex interaction mode in a Mach 2.5 flow is presented. The vortex dynamics of interest were targeted by placing expansion ramps of the same height with a mutual overlap distance on the surface of a strut injector specifically designed for the study of multiple vortex interactions in supersonic flow. The experiments were performed in the supersonic wind tunnel facility of the Aerodynamics Research Center at the University of Texas at Arlington. This investigation complements and expands on previous studies that have primarily focused on the dynamics and merging characteristics of large-scale streamwise, turbulent, vortical structures, in order to augment the understanding of the effects of the resulting flowfield on the mixing processes. Non-intrusive measurements based on the laser diagnostic technique of Filtered Rayleigh Scattering have been used to measure the concentration of an injected passive scalar (helium) at two planes downstream of the injection point. The injection scheme characterized by an imposed vortex dynamics scenario is investigated and timeaveraged plots of helium concentration are calculated. The data related to helium concentration are then compared with the flowfields provided by Stereoscopic Particle Image Velocimetry to identify key controlling parameters of the injection scheme under investigation to assess the influence of the resulting streamwise vortex interactions on the mixing process. An estimate of the peak helium concentration decay rate is found using the data obtained from the two streamwise stations.