Exploration of Optimal Propulsion System Airframe Integration Design Concepts for a Low Boom Supersonic Aircraft

We present several approaches on propulsion system airframe integration design concepts for supersonic aircraft to obtain an appreciable decrease in sonic boom loudness level. Propulsion system integration affects the ground pressure signature of a supersonic aircraft through three main factors which are; distortion of the free-stream flow by engine inlet/outlet flow conditions due to high temperature and pressure values, the location of the engine(s), and the structural deformations caused by the propulsion system loading. In this paper, we focus solely on the effects of engine inlet/outlet flows and the location of the engine on the aircraft. CFD simulations are performed for benchmark models provided by AIAA Second Sonic Boom Prediction Workshop for these two factors. Firstly, four different engine locations are considered on the Jaxa-Wing-Body (JWB) low-boom model, and the effect of engine location on the sonic boom is investigated. The inlet and outlet flow conditions are selected the same as the ones for the C25D concept aircraft. Next, two different configurations of 2-D external compression supersonic inlets and a minimum length nozzle are designed using the compressible flow relations and the method of characteristics respectively. To predict the effective inlet and nozzle performances before the airframe integration process in a 3-D model, empirical formulas are used to calculate the spillage and boat-tail drags for the inlet and nozzle components. The two-ramp configuration resulted in a lower spillage drag than the three-ramp configuration. A correlation between empirical and numerical solutions is observed through the design and integration phases of the propulsion system. Finally, the propulsion system components are integrated into a 3-D JWB model with a designed pylon to assess the sonic boom loudness. A difference of 10 dB in-vehicle loudness level is encountered for the aircraft models with and without propulsion system integration. The effect of different inlet configurations on the sonic boom of the overall aircraft is seen to be less significant. However, a two-ramp configuration provided better total pressure recovery and mass flow ratio. The effect of the pylon on the nozzle performance and the near field pressure distribution is observed to be more significant and further investigation is recommended as a future study.