Effect of upstream injection and pylon downstream of the cavity on the mixing characteristics

Abstract

Flame stabilizers employing pylons within scramjet engines are becoming more prominent for enhancing fuel penetration and mixing. Studies have highlighted the enhanced mixing efficiency achieved by positioning a pylon ahead of the cavity. Nonetheless, the potential of a pylon positioned downstream of the cavity has not been thoroughly examined. To bridge this gap, the present study explores the effects of fuel injection when a pylon is positioned downstream of the cavity, as well as investigates injection upstream of the cavity. Numerical simulation is employed, utilizing a hybrid Reynolds-averaged Navier–Stokes/large eddy simulation simulation with an improved delayed detached eddy simulation turbulence model. To gain a deeper understanding of the mixing dynamics, additional investigation using dynamic mode decomposition has been performed. The upstream injection with a pylon downstream of the cavity has an improved mixing performance in comparison to the cases without it. The pylon placed downstream also assists in increasing the penetration height. The placement of the pylon leads to an increase in the total pressure loss. The low-frequency vortices are observed within the cavity due to back pressure caused by the pylon. Large-scale and higher-frequency vortices are observed downstream of the pylon. It is found in the modal analysis that the low-frequency vortices within the cavity and high-frequency modes downstream of the pylon enhance the mixing. The acoustic loading is observed to be higher when the pylon is placed downstream of the cavity.