Análise analítica e numérica do escoamento em um veículo lançador de CubeSats aplicando a tecnologia da combustão supersônica no segundo estágio de propulsão

Abstract

Current rocket engines have a low specific thrust compared to the airbreathing propulsion technologies. Airbreathing supersonic combustion engines/vehicles are an alternative to improve the efficiency of access to space in a flight through the dense Earth’s atmosphere, below 60 km of geometric altitude. In this work, aerodynamic analysis of the conceptual model of supersonic combustion engine/vehicle (scramjet) was carried out to operate as a second-stage propulsion engine of a nanoSats launch vehicle. Two engineering approaches, analytical and computational numerical methodology, were used to perform the preliminary analysis of the proposed scramjet model, coupled to the third propulsion stage, at an altitude of 20 km with flight speed equivalent to Mach 5.8. Atmospheric air was considered a calorically perfect gas, and the viscous effects were neglect in a preliminary analysis. Supersonic combustion was modeled as heat adding to the supersonic flow without fuel injection. Then, numerical simulations were carried out considering the effects of the boundary layer development to verify the aerodynamic feasibility of the model. Optimization of the compression angles at the scramjet compression section was used to minimize the entropy generation and increase the vehicle’s compression efficiency, aiming to reach the temperature and Mach number at the combustion chamber entrance. The temperature required at the combustion chamber entrance is estimated to self-ignite the air-fuel mixture. Korkegi limit was evaluated through oblique shock waves in the compression section and in the heat addition process. Using the Korkegi limit, in the preliminary analytical design, as an indication of unstart due to the separation of the boundary layer caused by the adverse pressure gradient, we investigated to identify in numerical simulations considering the viscous effects whether the unstart phenomenon would occur. Numerical simulations were performed using commercial software, ANSYS Fluent, using the turbulence model known as transition SST. We also performed mesh convergence tests, numerical experiment validation on top of numerical data validated by HyShot flight data. Both meshes used in the validation and the analysis of the present work have equivalent levels of refinement in the direction of the wall, satisfying the condition of the turbulence model (𝑦 + < 1). The analytical calculations showed good quantitative and qualitative consistency with the numerical simulation results considering the same