Aerodynamic Characteristics of the Retro Propulsion Landing Burn of Vertically Landing Launchers

Abstract In the frame of the European funded H2020 project RETALT (Retro Propulsion Assisted Landing Technologies) the unsteady aerodynamics of vertically descending and landing launchers have been investigated. In this paper experimental data of the landing burn tested in the Vertical Free-Jet Facility Cologne (VMK) at DLR in Cologne is presented. The landing burn was simulated with a cold gas jet of pressurized air opposing the wind tunnel free stream. Tests with several jet conditions were compared to results without active jet. Proper Orthogonal Decomposition of Schlieren recordings and spectral analyses of their time histories are performed and are compared to frequencies in pressure measurements. Dominant frequencies were found, which are strongest at Mach 0.8. Especially a Strouhal number of 0.2 was found to be most dominant. The intensity of the dominant frequencies, can be lowered if the engine is active. The normalized root mean square pressure fluctuations are between 0.1 and 0.3 during the landing maneuver. Additionally, the steady flow features scale well with the ambient pressure ratio and the momentum flux ratio.