Investigation of shock structure and aerothermodynamics of stepped ramp scramjet inlet in hypersonic rarefied flow

Numerical investigation is carried out to study the flow characteristics of a two-dimensional scramjet inlet with stepped ramp configuration in rarefied hypersonic flow using Direct Simulation Monte Carlo (DSMC) method. Two types of step configurations modeled for this study, namely step-up with a step height of 2 mm and 3.5 mm and step-down with a step height of 2 mm. The step is positioned at 50 and 70 mm at the ramp from the leading edge for both configurations. The Stochastic PArallel Rarefied-gas Time-accurate Analyzer, a DSMC solver that provides accurate results analogous to the Boltzmann equation is used in the present simulation. The freestream (Air) Mach number of 12 and temperature of 208 K with the Knudsen number of 0.02 considered for this simulation. The Variable Hard Sphere (VHS) and Larsen-Borgnakke model is used for the modeling of collision and energy exchange reactions. A diffuse reflecting surface with full thermal accommodation and a constant wall temperature of 300 K is used. The simulations precisely predict the flow physics such as multiple shock structures, flow property (velocity, temperature, and pressure) variations and surface property (heat transfer coefficient and skin friction coefficient) variations in and around the scramjet inlet. The present simulation provides valuable insights into the shock structures and shock polar, as well as scramjet inlet performance in terms of total pressure recovery, flow distortion, kinetic efficiency, and thrust.