Effect of injection location on mixing characteristics with pylon downstream of cavity

Scramjet propulsion holds promise for high-speed travel and reusable satellite launches, but fuel combustion at supersonic speeds presents a challenge. Limited retention time hinders proper air-fuel mixing. While placing a pylon upstream improves mixing, its impact downstream remains unexplored. This study investigates the effects of different fuel injection locations within the cavity on mixing performance. Numerical simulations with the Improved Delayed Detached-Eddy Simulation (IDDES) turbulence model are used to examine various injection locations. The study found that placing the pylon downstream significantly altered flow patterns. This led to the formation of additional vortices and better mixing downstream and within the cavity. The penetration height is also augmented due to the presence of a pylon. Different injection locations varied in mixing efficiency, penetration height, and total pressure loss, with normal-flow injection close to the cavity's aft showing better overall mixing performance. Dynamic Mode Decomposition (DMD) analysis provided insights into mixing improvement mechanisms, highlighting the effect of injection strategies on flow dynamics and relation with pressure spectra. DMD modes showed distinct dominant frequencies for each injection case, influencing lateral mass and momentum exchange within the cavity and affecting shock interactions. The findings underscore the significance of judiciously selecting injection positions, accounting for mixing efficiency, penetration height, and total pressure loss.