Air-Fuel Mixing in HyShot-II Scramjet: Analysis of Golden-Ratio Elliptical Injector Designs

The efficiency of air-fuel mixing in scramjet combustors is crucial for achieving hypersonic speeds, as the residence time is in milliseconds. A study of air-fuel mixing for different injector designs in the HyShot-II scramjet combustion chamber was performed. This work focuses on a numerical study on mixing efficiency as hydrogen is injected at sonic speed into a 2.4 Mach number air cross-flow. Numerical simulations with three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations and the k-w Shear Stress Transport (SST) turbulence model investigate an elliptical injector, in addition to the impact of adding a fin ahead of the injector. The study was conducted on non-reacting flow to isolate the mixing process from combustion effects. Key aspects include validating the computational model against a theoretical framework, the capability to capture general vortex structures, and expanding the research by employing Delayed Detached Eddy Simulation (DDES) to investigate unsteady flow phenomena on the design that offered larger improvement in air-hydrogen mixing. Increases in jet penetration height and circulation were observed, which improved mixing but incurred in additional pressure losses. RANS results showed 6% improvement in mixing efficiency with the elliptical injector and up to 38% increase with the ellipse and fin combination, and 28% with DDES. Hydrogen jet penetration increased by 5% with the elliptical injector and 150% with fin addition.