Improving Scramjet Performance Through Flow Field Manipulation

In airframe-integrated scramjets, nonuniform compression fields combine with thick boundary layers developed over the vehicle forebody to deliver density stratified flow to the combustor. Additionally, in high-Mach-number scramjets fueled with wall-based injectors, delivering fuel to engine centerline air is challenging, typically relying on turbulent mixing through long combustors. This study exploits the interaction between the density-stratified flow and the vortices generated by a strategically positioned injector in the inlet to manipulate the flow field, redistributing oxygen in captured air to more accessible locations. A numerical study was performed, examining the Mach 12 rectangular-to-elliptical shape-transitioning engine flow path. With the inlet compressing air into a high-density cowl-side core-flow, hydrogen injection here through a “manipulator jet” imparts vorticity through the bulk of the engine mass flow. This high-penetration injector allowed hydrogen to pierce the core-flow, aided by the engine’s natural shock train. The injector-induced vortices ensured that centrally located and previously inaccessible air was redistributed to the more accessible cowl-side combustor surface. When combined with supplementary injectors, combustion efficiencies exceeding 80% were achievable 3.6 combustor-heights further upstream than with previous fueling configurations. These improved mixing and combustion rates suggest that combustor length could be reduced in future studies.