AERODYNAMIC CHARACTERIZATION OF IN-AIR CAPTURING VEHICLES USING CFD SIMULATIONS

The sustainability of the complex, high performance, high-cost rocket stages and engines has drawn attention to the innovative return modes with the aim of bringing them back to their launch site. One of the return modes, in-air capturing (IAC), where a reusable launcher vehicle (RLV) is towed back by an aircraft with the assistance of an aerodynamically controlled capturing device (ACCD) which helps to connect the two vehicles. This return mode is found to be more promising as it eliminates the additional propulsion system during the descent which reduces the mass and the cost of the system. The first and integral step of IAC requires the two vehicles to be in a parallel formation for at least 60s to enable the ACCD released from the aircraft to reach the RLV. This would require both vehicles to maintain similar aerodynamic performance to achieve comparable velocities and altitude. Typical long-range commercial aircrafts have a lift to drag ratio between 17 to 19. However, during IAC, this ratio must be brought down to a value of around 6 for the vehicles to remain within the capture envelope. Empirical methods are typically used to determine the optimum capturing aircraft configurations by combining the drag generated by the various components [1]. However, the drag components create additional turbulence structures that the empirical methods are unable to estimate. Therefore, it is important to critically analyse the formation flight configurations using high-fidelity CFD simulations, while taking into consideration the atmospheric perturbations. In this paper, the methodology for the high-fidelity simulations is presented. A sensitivity study is performed on the type of boundary conditions, the choice of the solver, the domain size and turbulence model, by referring to experimental results obtained on a NACA 0012 airfoil. Best practice guidelines are then applied to all three vehicles: the towing aircraft, the ACCD and the RLV alone, with the aim of providing high-fidelity aerodynamic data for different angle of attacks. This paper is a part of H2020 FALCon project and continuation of the work by Singh, S. et al. (2021). [1] Singh, S.; Stappert, S.; Bussler, L.; Sippel, M.; Buckingham, S.; Kucukosman, C.: A Full-Scale Simulation and Analysis of Formation Flight during In-Air-Capturing, IAC-21-D2.5.2, 72nd International Astronautical Congress (IAC) Dubai, October 2021)