Aerothermal Analysis of a Rocket Booster during Reentry and Retro-propulsion

Abstract

In recent years the use of re-usable launch vehicles for payloads intended for earth orbits has gained popularity where retro-propulsion, when the engines are firing in the same direction of flight, is used to land the vehicles. Private companies such as SpaceX, Blue Origin and Rocket lab are developing reusable rocket boosters where the most prominent is the Falcon 9 rocket by SpaceX. To reduce costs for European space travel the European Space Agency (ESA) has funded several projects within reusable rocket boosters. The RETPRO and RETALT project was done to investigate the system components of a reusable rocket booster along with a CFD and wind tunnel verification of aerothermal calculations. GKN Aerospace is involved in the development of the Prometheus engine which utilizes a gas generator cycle that runs on liquid methane and liquid oxygen. This engine will power the European rocket demonstrator Themis which is a proof of concept of a reusable first stage rocket. In this thesis Computational Fluid Dynamics simulations were used to analyse the aerodynamic and thermodynamic loads on and around the nozzles. The heat transfer coefficient (HTC), temperatures, pressures and heat flux were investigated at the start and end of a reentry burn. Different chemical models were investigated with the aim to find the appropriate model in terms of computational cost and accuracy for simulating the reentry and retro-propulsion. It was found that for reentry without retro-propulsion the frozen chemistry model provides sufficient accuracy with lower computational cost compared to the chemical non-equilibrium model and was therefore chosen for all simulations when the engines were off. With retro-propulsion, however, the chemical non-equilibrium model was needed to accurately model the temperatures and heat flux on the rocket walls. It was concluded from the results that the largest HTC where found at the end of the burn and when the engines are off the highest HTC is located near the throat of the outer nozzles while during retro-propulsion it’s the center nozzle that is most exposed to high local HTC near the nozzle exit.