Performance Evaluations of the STRATOFLY MR3 Propulsive Nozzle at Supersonic Speeds

The aim of shortening the long haul flights, reducing the climate impact and air space congestion increase the interest in hypersonic civilian vehicle transportation research. In order to achieve such goal, the EC founded STRATOFLY project proposes a design which is capable of carrying 300 passengers with the cruise speed of Mach 8 at the altitude higher than 30 km above the ground in the stratosphere. Considering the wide range of the flight speeds covered by the trajectory, a combined propulsion system, which is one of the many critical technologies required to realize this vehicle, is under investigation within the project. Combined propulsion plant embodies six Air Turbo-Rocket (ATR) engines to propel the vehicle from idle till supersonic speed and a Dual-Mode Ramjet (DMR) engine to satisfy the requirements for hypersonic acceleration and cruise condition at Mach 8. These two types of engines co-operate to accelerate and propel the vehicle for a wide speed range including the supersonicto-hypersonic transition. The exhaust streams of these engines are fed to a shared nozzle in which complex flow physics occur due to the mixing and recirculation. In order to assess the flow field inside the propulsive nozzle and estimate the performance of the combined cycle engine at various regimes, a recently developed compressible solver, on the OpenFoam platform,has been used. Flow field investigations inside the propulsive nozzle at different supersonic operation points of the flight trajectory showed that, the mixing of ATR and DMR exhaust streams causes a separation bubble which drops the performance of the propulsion system. It has been seen that, as the size of this separation region changes according to different Mach numbers, its effect on the performance of the propulsion system also changes. The location of shock waves and expansion fans inside the nozzle are mainly dependent on the static pressure downstream of the ATR and DMR combustion chambers, which drastically changes the flow field features. Finally, the performance of the propulsion system has been analysed in terms of the macroscopic parameters e.g. gross thrust and total pressure losses.