Reconstruction of Wind Tunnel Tests using CFD for a Reusable First Stage during Rocket Retro-Propulsion

Abstract

The RETPRO project (Validation of Wind Tunnel Test and CFD Techniques for Retropropulsion), as part of ESA's Future Launcher Preparatory Programme, aims at preparing the tools, necessary for a reliable design and simulation of future rocket launchers or spacecraft. A particular focus is assigned to vertical take-off and landing configurations using retro propulsion as part of their control concept for entry, descent, and landing manoeuvres. Wind tunnel tests and computational fluid dynamics are used to generate a comprehensive aerodynamic database, which is required for flight dynamics simulations, enabling mission and performance analyses of possible future launcher designs. This paper focuses on the presentation and discussion of steady-state numerical simulation results which reconstruct selected wind tunnel tests during both powered and unpowered descent phases. The CFD simulations cover a Mach number range from 2 up to 7, with dry air used to model the exhaust plume. Typical flow topologies and features are discussed, with quantitative results coming from a comparison of force balance and surface pressure measurements between experimental results and CFD simulations. Schlieren images from the experiments are used to evaluate the plume structure and shock stand-off distances. For the unpowered descent cases the agreement between schlieren images, force and pressure measurements is extremely strong. During powered descent the basic plume structure is captured well despite the highly unsteady and fluctuating flow field. Pressure and force measurements gave mixed results, but overall the studies show that RANS simulations perform well compared to experimental data.