The Influence of a Retro-Propulsion Plume on Vehicle Aerodynamics and Aeroheating during Hypersonic Re-Entry

Abstract

During the return to earth phase of a re-usable first stage, a hypersonic retro-propulsion burn is initiated as it re-enters the atmosphere. The aerodynamic coefficients, as well as the aerothermal heating are heavily influenced by the presence of the retro-plume, and can impact the effectiveness of the control surfaces as well as the thermal protection strategy.

This paper presents an aerodynamic and aerothermal analysis conducted using the DLR flow solver TAU on the RFZ model, a generic configuration based on the SpaceX Falcon 9. The trajectory point of interest is the start of burn, which occurs at a Mach number of 7.14 and an altitude of 50 km. This represents the transition phase of re-entry where the high-altitude glide ends (engines off) and the powered descent begins (engines on). A sensitivity study was conducted to understand the influence of angle of attack (0 to 12 degrees) on heat loads and aerodynamic coefficients both with and without plume.

Sample results for both the glide and powered descent phase are presented below in Figure 1. The flowfield without active engines is characterised by a strong bow shock located close to the nozzle exit planes. The presence of the highly expanded retro-plume increases the stand-off distance significantly, providing a shielding effect from the incoming high-speed flow. A contact surface forms where the flow stagnates and streamlines coalesce, redirecting the airflow around the plume, where multiple recirculation regions can be observed. Later studies including the influence of angle of attack show skewed plume structures which result in asymmetric heat-flux patterns across the various components of the booster. This is the first of many test cases for a re-usable launcher using a standardised, open-access geometry and trajectory. These results will be made openly available to the research community to promote collaboration in understanding the design challenges associated with re-usable launchers.