Study of Direct Gas Injection into stagnation zone of Blunt Nose at Hypersonic Flow

Direct gas injection in the shocked or compressed region has importance in many applications from drag control to ignition and pressure gain combustion. This numerical study is focused on direct light gas injection into the stagnation zone of a blunt nose at hypersonic speed, aiming to achieve efficient active drag control. The direct injection of a inert gas helium and a reactive gas hydrogen in the stagnation zone of bow-shock, are compared numerically with the air injection at hypersonic flow Mach 6 with freestream conditions according to the Earth's altitude of 10 km. The two-dimensional axisymmetric numerical simulations are performed by adaptive mesh refinement and solving compressible Euler equations for multiple thermally perfect species with a reactive source term using AMROC solver. The hydrogen combustion and ignition is modelled using one-step reaction mechanism. The pressure drag on the blunt nose has been compared for different injection pressure ratios for all three gas injections and it was concluded that the sonic injection (at Mach = 1) of light gases He and H-2 provides similar performance in the pressure drag reduction up to 77 %, as compared to air injection, with 62.5 % and 73.5 % lesser mass flow rate, respectively. In case of supersonic gas injection (at Mach = 2), the inert gas helium injection performs relatively better (up to 82% pressure drag reduction) or comparable to supersonic air injection for lesser mass flow rates. Various flow features in the short and long penetration modes of sonic and supersonic gas injections are also analyzed in the reactive and non-reactive flow-fields.