Rocket nozzle cold-gas flow velocity measurements using laser-induced gratings

Abstract

The heterodyne detection laser-induced electrostrictive gratings technique was employed for characterization of a flow velocities field in the plume of a rocket nozzle. The intention of the work was to validate CFD calculations, that predict the appearance of a recirculation zone inside the flow at a certain ratio of nozzle and ambient pressures. This zone co-existswith the side loads to the nozzlewall thatwere observed experimentally as transient forces during the start-up or the shut-down of the thrust chamber. Measurements were performed in cold-gas flows from a subscale thrust-optimized, parabolic nozzle. Nitrogen at stagnation pressures up to 40 bar was supplied to the nozzle. The experimental results clearly proved the existence of a recirculation zone in the flow field, in a reasonable agreement with the predictions of CFD calculations.