Stability and transition for long-duration hypersonic flat-plate boundary layer considering wall thermal effect

Current flight tests and wind tunnel experiments face challenges in obtaining long-duration hypersonic flow processes and thermal environments. Numerical simulation is an effective tool to study wall thermal effects—thermal radiation heat exchange and internal thermal conduction—and their influence on flow transition. This study employs linear stability theory (LST) and direct numerical simulation to analyze a 10-mm-thick C/SiC composite flat plate under three Mach numbers (6, 10, 15) at 30 km altitude, considering internal thermal conduction. The results of hypersonic base flow, flow stability, and transition are compared with and without surface radiation under long-duration conditions. Results demonstrate that the wall temperature ratio (Sw = Tw/T0) serves as a key indicator of wall thermal effects: larger Sw increments correlate with enhanced wall thermal effects. Surface radiation suppresses the temperature rise at the wall, resulting in decreased Sw increments. Sw (with/without radiation) decrease along the streamwise direction while increasing over time. Wall thermal effects increase boundary layer thickness and induce significant modifications to the base flow profile. Larger increments in Sw occur near the plate leading edge, indicating stronger wall thermal effects in this region. LST analysis shows that wall thermal effects shift the second-mode instability to lower frequencies, reduce maximum growth rates, and delay transition locations. Higher Mach numbers reduce the Sw increment, diminishing wall thermal effects and consequently the transition delay extent.