Computational Investigation of an Improved Cowl Concept for Hypersonic Propulsive Nozzles

Abstract : The effects of placing a gas generator into the cowl of a hypersonic nozzle/afterbody were investigated computationally. Gas generator mass flow and deflection angle effects were analyzed for two nozzle/cowl geometries; an experimentally validated nozzle/cowl configuration evaluated at off-design conditions and a generic hypersonic propulsive nozzle evaluated at more realistic on design conditions. A combination of Van Leer flux-vector splitting and Roe flux-difference splitting finite volume computational algorithms were used to solve the unsteady two-dimensional Navier-Stokes equations based on planar, laminar flow, perfect gas equation of state assumptions. For the low speed off-design cases analyzed, gas generator effects on nozzle wall pressure recovery were similar to geometric cowl extension and deflection effects. Nozzle wall pressure recovery increased with increased mass flow. Gas generator deflections towards the nozzle wall provided dramatic improvements in pressure recovery and only small penalties were paid for deflections away from the wall. As the combustor exit pressure and trajectory Mach number increased, the nozzle flow became increasingly dominated by large initial expansions which minimized the overall effects of the gas generator and tended to push the gas generator effects on nozzle wall pressure recovery further downstream. Hypersonic nozzle, Navier-stokes solutions, Laminar, Unsteady flow, Flux-vector splitting, Flux difference splitting.