Effect of geometrical parameters on the mixing performance of cantilevered ramp injectors

A cantilevered ramp fuel-injection strategy is considered as a means to deliver rapid mixing for use in scramjets and shock-induced combustion ramjets (shcramjets). The primary objective is to perform parametric studies of the injector array spacing, injection angle, and sweeping angle at a convective Mach number of 1.5. Analysis of the three-dimensional steady-state hypersonic flowflelds is accomplished through the WARP code, using the Yee-Roe flux-limiting scheme and the Wilcox k-w turbulence model, along with the Wilcox dilatational dissipation correction. A closer array spacing is shown to increase significantly the mixing efficiency in the near field, and a direct relationship between initial fuel/air contact surface and mixing efficiency growth is apparent. A change in the injector angle from 4 to 16 deg induces a 9% augmentation in the mixing efficiency but more than a twofold increase in the thrust potential losses. A sweeping angle of -3.5 deg is observed to result into significantly better fuel penetration, translating into a 28% increase in the mixing efficiency for a sweep angle decreased from 3.5 to -3.5 deg. It is observed that an air cushion between the wall and the hydrogen is sufficiently thick to prevent fuel penetrating the boundary layer when 1) the fuel is injected at an angle of ∼10 deg or more, 2) an array spacing of at least the height of the injector is used, and 3) a swept ramp configuration is avoided.