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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-exists with the side loads to the nozzle wall that were 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.

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