Hypersonic Retrograde Propulsion Experiments A Basis for Validation of CFD within RETPRO
Creators: name:  D. KIRCHHECK 
name:   A. MARWEGE 
name:   J. KLEVANSKI 
name:   A. GULHAN 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: REUSABLE SYSTEMS
FLIGHT PHYSICS
DYNAMICS

description: The RETPRO project (Validation of Wind Tunnel Test and CFD Techniques for Retro-propulsion), as part of ESA\'s Future Launcher Preparatory Programme (FLPP), aims at preparing the tools, necessary for a reliable design and simulation of future rocket launchers in view of the European goal to access the field of re-usable launchers using retrograde propulsion for vertical powered descent and landing. The tools, that are necessary for an aerodynamic design include Wind Tunnel Tests (WTT) and Computational Fluid Dynamics (CFD) to generate a comprehensive Aerodynamic/Aerothermal Database (AEDB/ATDB), which is essential for flight dynamics simulations, enabling mission and performance analyzes of a potential future launcher design. The validation of WTT and CFD techniques is performed by both, complementary and comparative experimental and numerical studies on common reference test cases, with a close link to currently operational vehicles. Included are down-scaled wind tunnel tests in the hypersonic, supersonic and subsonic regimes, using pressurized air and hot gas from a model-integrated combustion chamber to simulate the retro-propulsive jets. The results will provide a valuable foundation for validation of CFD codes in the respective flow regimes, ultimately being facilitated to extrapolate the established models to flight relevant scales in order to populate the databases for final flight analyzes. In that scope, the present paper focuses on the wind tunnel experiments in the Mach number range between 5.3 and 7.0, conducted in the Hypersonic Wind Tunnel (H2K) at DLR, Cologne. The test conditions are set up to duplicate a high-altitude, so called, re-entry burn maneuver, similar to the flight profile of SpaceX\'s Falcon 9, which serves as basis for the underlying reference configuration, that was already presented in 2019. The model is equipped with a 4- or 6-component strain gauge balance to measure aerodynamic forces, depending on the upstream flow topology from zero, one, or three active engines at different thrust vector configurations. The flow topology is additionally being assessed, using Schlieren optical visualization. The pressure field is characterized at selected locations on the nozzle base plane and along the cylindrical body using high-frequency pressure transducers. The different measurement techniques are used to work out sensitivities from several parameter variations, including different deflections and types of control surfaces, comparing grid fins and conventional planar fins. The paper introduces the underlying reference configuration, the design, and the capabilities of the wind tunnel model. It provides an overview on the general flow properties under variation of internal and external flow conditions, as well as geometrical parameters. Finally, the goal is to evaluate the gathered data with regard to it\'s applicability for CFD validation of a powered descent flight maneuver in hypersonic ambient flow.