Impact of Retro Rocket Plumes on Upper Stage Aerothermodynamics during Stage Separation

Abstract

In this paper, an extensive investigation of the separation process of the first two stages of a carrier rocket that employs solid rocket motors for the lower stage is presented. As the reference vehicle, the VEGA rocket is used. The effect of the plumes of first-stage retrorockets on upper-stage aerodynamics and aerothermal loads is analyzed by means of wind-tunnel testing in the hypersonic wind tunnel H2K of DLR, German Aerospace Center. Aerodynamic coefficients are determined by force measurements. In addition, pressure distributions on the upper-stage surface and schlieren images for flow visualization are recorded. Infrared thermography measurements are conducted to determine the effect on aerothermal loads. Different flow conditions are achieved by variation of Reynolds number, retrorocket injection pressure ratio, and angle of attack. Results showed extensive flow separation around almost the entire upper stage by the retrorocket plumes already at low injection pressure ratios. During angle-of-attack sweeps, sudden changes in the flow structure occurred accompanied by strong changes in aerodynamic forces at values of α≈±2  deg. This behavior was found to be influenced by hysteresis effects.