Analysis of Influencing Factors of Boundary Layer Transition During Ascent Phase of Hypersonic Vehicle

The transition of the boundary layer is an important issue that must be considered in the design of hypersonic ve-hicles. During the ascent phase of the vehicle, both the Mach number and the flight altitude increase simultaneously and af-fect the location of transition jointly. This paper investigated the plate boundary layer and employed linear stability theory and e^N method to study the influence of Mach number and flight altitude on the stability of boundary layer and the transition process during the ascent stage of hypersonic vehicles (Mach number ranges from 4 to 6, and flight altitude ranges from 14 km to 25 km). The research findings indicate that the second mode, which dominates the transition in the boundary layer, becomes more unstable with increasing Mach number. However, it tends to be more stable with increasing flight altitude. Furthermore, the stability of the boundary layer at typical trajectory points during the ascent phase of HIFiRE-1 was ana-lyzed. It is observed that under the combined influence of Mach number and flight altitude, the growth rate of the second mode initially increases and then decreases in ascent stage, resulting in a non-monotonic phenomenon where the transition location shifts forward initially and then moves backward.