Passive Strut-Driven Mixing Enhancement in Supersonic Combustion: A Computational Approach

Efficient fuel-air mixing remains a major challenge in supersonic combustion due to the extremely short residence time and strong compressibility effects associated with high-speed flows. To address these challenges, a triangular passive strut is introduced downstream of a two-strut arrangement to modify the local shock structure and enhance vortex formation inside the combustor. Numerical simulations are performed using the compressible unsteady Reynolds-Averaged Navier-Stokes (URANS) equations coupled with the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model. Hydrogen is injected at sonic velocity through circular ports located on the strut surfaces. The results reveal that the downstream passive strut significantly alters the reacting flow field by generating stronger shock-wave interaction, larger recirculation zones, and enhanced streamwise vortex structures, which improve transverse fuel penetration and fuel-air interaction inside the combustor. Compared to the baseline single-strut combustor, the passive-strut configuration produces a wider high temperature region and stronger heat release distribution in the downstream region. The larger recirculation zones generated by the passive strut also increase the residence time of the reactants without introducing substantial total pressure loss. The combustion characteristics are further analyzed using the Takeno flame index, which indicates improved partially premixed combustion behavior and more organized reaction zones in the passive strut configuration. Additionally, the combustion efficiency increases significantly (86%) compared to the baseline configuration due to improved fuel-air interaction throughout the combustor length. The study demonstrates that the downstream triangular passive strut acts as an effective passive flow control device for enhancing mixing and combustion characteristics in compact supersonic combustors without requiring active flow control techniques.