Effect of passive strut angle on the vortical structures and mixing characteristics of scramjet combustor

Scramjet is considered as the future of high-speed transportation and reusable launch vehicle for satellite placement. However, the combustion of fuel at supersonic speeds is a challenge. Since combustion takes place at high velocities, analyzing the mixing of air and fuel in the engine is important for enhancing performance. The current study focuses on two passive struts that are placed at a short distance downstream of the fuel injection strut. Diverging angles of these passive struts are varied to assess the effect of the mixing and corresponding acoustic behavior. The computational study is conducted using an improved delayed detached-eddy simulation turbulence model. The single strut scramjet configuration is taken as a benchmark to compare it with different strut configurations. The mixing efficiency is highly affected by the divergent angle of the passive strut. Mixing performance enhances as the back-pressure increases due to the passive strut. If the back-pressure becomes too high due to the divergence of the passive strut angle, then the unstart phenomenon is observed. Pressure loss is observed to decrease with a decrease in the divergence angle of the passive strut. As the divergence angle of the passive strut configuration increases, low-frequency vortices are generated. The modal analysis shows the low-frequency modes responsible for the enhanced mixing performance. Overall sound pressure level increases with an increase in the divergence angle of the passive strut.