Planar Rayleigh Scattering Measurements of Shock Enhanced Mixing

[摘要] This investigation was concerned with the mixing which occurs after the unsteady interaction of a shock wave with a laminar jet of helium. The jet of helium was injected normal to the direction of the propagation of the shock. The vorticity created at the boundaries of the jet during the shock interaction generates a stream of air which divides the initial circular cross section of the jet into two lobes. Each lobe is further divided into a tail region and a vortex core. The vortex cores from each lobe form a vortex pair that pulls ahead of the tail regions. In the present investigation the primary diagnostic, planar Rayleigh scattering, had sufficient spatial and temporal resolution to resolve the smallest diffusion scales present and allowed helium mole fractions to be measured in two-dimensional planes normal to the original jet flow direction. The amount of molecular mixing was evaluated with a mass distribution function at increasing times after the shock interaction. The total masses of helium contained in regions where the molar concentration of helium was at least 30% and 50% were also calculated. The shock Mach number was varied, and the effect of a reflected shock was studied. The velocity and spacing of the vortex pairs was measured. It was found that shock interactions can significantly increase the mixing between the air and helium. As the Mach number increases, better mixing occurs as the stream of air divides the jet. However, less mixing occurs at the later times when the vortex pairs are moving ahead of the tails. A rough collapse of the mixing data occurs when time is normalized with the change in velocity of the air behind the shock. The measured velocities and estimated values of the circulation agree very well with previous computational results. An increase in the enhancement of mixing occurred after the interaction with the reflected shock.

[发布机构] University:California Institute of Technology;Department:Engineering and Applied Science

[关键词] Aeronautics and Physics