Effect of Wall Temperature on Hypersonic Boundary Layer Transition over a Compression Ramp

This work investigates the effects of isothermal wall temperature variation on boundary layer transition and separation dynamics in Mach 7.7 flow over a 15-deg compression ramp. The compressible Navier-Stokes equations for an ideal gas are solved using the MEG-C scheme for convective terms and an alpha-damping method for viscous terms. Inner-layer dynamics are modeled using the Compressible Equilibrium ODE Wall-Stress Model. Three wall-to-stagnation temperature ratios are considered: T_w/T_0 = 0.09 (colder), T_w/T_0 = 0.18 (baseline), and T_w/T_0 = 0.36 (hotter). Results show that colder wall temperatures shift transition upstream of the separation bubble, significantly reducing its size. Although peak heat transfer increases in the cold case, its spatial extent is reduced, and the overshoot decays more sharply, indicating more abrupt transition to turbulence. In contrast, hotter walls cause earlier separation, delayed reattachment, delayed transition onset, and dampened high-frequency disturbances. Proper Orthogonal Decomposition (POD) of the density fluctuation field reveals distinct differences in modal energy content, dominant structures, and spectral distributions across the cases. These findings underscore the strong influence of wall temperature on transitional shock/boundary layer interaction behavior in hypersonic flow.