Analysis of Dual-Mode Hydrocarbon Scramjet Operation at Mach 4-6.5

Abstract

Reynolds averaged Navier ‐Stokes calculations have been performed for a U.S. Air Force Research Laboratory/ Aerospace Propulsion Ofe ce scramjet combustor designed for Mach 4.0 ‐6.5 e ight. The combustor e owpath is unique in that it is entirely free of e ow obstructions with fuel injection from wall-mounted injection ports and e ameholding established by means of a recessed cavity. Calculations were performed at the minimum (Mach 4.0) andmaximum(Mach6.5)e ightdesign conditions.Thecombustoroperatedin dualmodeattheMach4.0condition. The precombustion shock train formed a region of low-momentum/separated e ow adjacent to the combustor side wall. This proved to be a primary source of e ameholding, with the recessed cavity adding additional e ameholding support. The e ow was notthermally choked at theMach 6.5 condition,resulting in very little upstream interaction. The mixing process at the Mach 4.0 e ight condition was considerably more efe cient than that seen at the Mach 6.5 condition, due primarily to the shock-induced e ow distortion and larger residence time. Even with the reduced mixing levels predicted at the Mach 6.5 condition, the combustion efe ciency was comparable to that achieved at the Mach 4.0 condition. The solutions obtained for dual-mode operation were particularly sensitive to choice of turbulence model and values specie ed for the turbulent Prandtl and Schmidt numbers. Overall, the solution sensitivity to grid resolution was small relative to the solution sensitivity to modeling uncertainties.