Hypersonic mixed-compression inlet shock-induced combustion ramjets

This study investigates the performance and flow field features of a mixed-compression inlet shock-induced combustion ramjet (shcramjet). In a shcramjet, oncoming air is compressed with shocks in the inlet and then further compressed and mixed with hydrogen fuel in a duct prior to shock-induced combustion and expansion of the combustion products through a divergent nozzle to provide thrust. Numerical studies are undertaken using the WARP code that solves the Favre-averaged Navier-Stokes equations closed by the Wilcox k-o turbulence model. Hydrogen/air combustion is solved via the twenty reaction, nine species combustion model of Jachimowski.; Mixing augmentation through the use of cantilevered ramp injector arrays on opposite shcramjet inlet walls is studied and the influence of relative array locations is quantified. Increased spanwise distance between adjacent injectors on opposite walls allows for increased jet penetration and fuel distributions in the center of the engine duct. Chemically reacting studies verify an air buffer is created between the fuel and walls that suppresses premature ignition while still allowing for an air based mixing efficiency of up to 0.46-0.54. Combustion is produced over aerodynamic wedges with the spatial flow variation dictating both detonation and shock-induced combustion can be present over constant angle wedges. The initial inlet angle must be as high as possible, while avoiding premature ignition, to generate the pressure in the combustor needed for significant positive thrust. Thrust production from combustion is found to be insensitive to wedge angle if combustion is initiated across the cross-sectional area. Strong recirculation regions are formed via shock/boundary layer interactions in the confined engine duct. Mitigation of the recirculation is demonstrated with correct placement of the nozzle expansion in conjunction with air blowing in the boundary layer at a mass flow rate on the order of that of the fuel injection. For flight at Mach 11 the mixed-compression inlet shcramjet is found to generate a specific impulse of 683 s in the simulation of a realistic three-dimensional flow field.