Variations of supersonic combustion modes induced by different wall temperatures in axisymmetric scramjet

The impacts of wall temperature on combustion mode variations are numerically investigated using Reynolds-averaged Navier-Stokes (RANS) simulations. A three-dimensional axisymmetric scramjet is employed to examine the flow, combustion, and operating performance under five different wall temperatures. The transition of the combustion mode from the cavity shear-layer stable combustion mode (CSL) to cavity-assisted jet-wake stable combustion mode (CAJW) is observed as the wall temperature increases from 900 K to 1200 K. The thermal and fluid positive feedback mechanisms cause the mutual enhancement between fuel reaction and flow temperature. The reduced mainstream velocity, complex wave structures, and an expanded primary recirculation region within the cavity are investigated with the increasing temperature. Within the wall temperature range of 300 K to 1500 K, the combustion efficiency increases from 0.58 to 1, and the total pressure loss increases from 0.52 to 0.58. The combustion, shock wave trains, and low wall temperature are the dominant contributors to the total pressure loss. The total pressure loss results in a maximum thrust loss of 24 N. Due to the enhancement in combustion efficiency and the reduction in convective heat losses, the actual exit thrust improves consistently, ultimately reaching a maximum value of 346.5 N.