CFD analysis of interaction effects between vehicles in formation flight for in-air capturing of reusable launchers

Abstract

Reusing the complex, high performance, high-cost rocket stages and engines by returning them back to their launch site is becoming important not only from economical aspects but also from an ecological point of view. An innovative return mode, ‘in-air capturing (IAC)’, is chosen as it provides potential for a better performance by reducing the overall fuel consumption, when compared to other approaches like vertical landing. In this mode, a winged reusable launcher vehicle (RLV), which has slowed down to subsonic velocity through atmospheric braking is captured using an aircraft and towed back to launch site. First, the vehicles approach each other in a parallel formation with similar velocities by keeping a safe distance between them. During this formation, a capturing device autonomously captures the RLV. Once the connection has been achieved, the captured configuration is pulled up from a gliding flight to cruise flight with a towing aircraft serving as an external propulsion system to the RLV. During these phases, the RLV is exposed to the wake of the towing aircraft and will face disturbances that will likely lead to a reduction in formation envelope. The impact of proximity between the capturing device and the RLV should also be evaluated to investigate the complex interactions which would alter the aerodynamic performances of both vehicles after connection. Moreover, in the next phase, the connected configuration must pull-up from a descent to cruise flight. For this the towing aircraft will be at high angle of attacks leading to strong downwash velocity in the wake that must be studied further. In this work, a full-scale three-dimensional RANS simulation will be performed with the open source CFD code OpenFOAM 6.0 using the k-ω SST turbulence model and a compressible solver rhoSimpleFoam to investigate aforementioned issues. The CFD results will be analysed to gain better insight in the flow field and interaction effects between the three vehicles and their aerodynamic performance used for the flight dynamics simulation of IAC.