Cold Gas Wind Tunnel Experiments of a Descending Launcher First Stage and Generalization of the Engine Scaling Parameter

In the Horizon Europe Project SALTO a demonstrator of a vertically landing first stage with three Prometheus engines was investigated, the so-called T3. It shall be recovered with a downrange landing approach. In this paper the results of cold gas experiments are presented where the engine plume was simulated with pressurized air. For that purpose, the engine scaling parameter, which is used to scale the engine parameters and thrust to the experimental conditions, was generalized. It was derived that a simplified engine scaling parameter can be found, with which the engine parameters can be scaled such that the thrust coefficient, momentum flux ratio, and ambient pressure ratio can be matched at the same time. The results of the test campaign showed that switches between the blunt and long penetration modes occur for T3, as the re-entry burn of the vehicle is performed at relatively low thrust coefficients. This can result in significant changes in the Cp values on the base area. The blunt mode shows lower Cp values and reduced pressure fluctuations. For cases with a single active engine at relatively high thrust coefficients, dominant frequencies were observed, which are driven by transitions between two flow-field modes within the blunt mode.