Wall Temperature Effects on High Enthalpy Hypersonic Boundary Layer Stability

The design of practical high-speed vehicles is constrained by the extreme thermo-mechanical surface loads which occur when traveling at high Mach number. This is further complicated by the dramatic increase in surface heat flux which accompanied with laminar-turbulent transition. Hence, understanding the stability characteristics of hypersonic boundary layers is crucial for advancing high-speed flight technology. At high-enthalpy conditions observed during high Mach number flight, real gas effects such as molecular dissociation significantly alter flow characteristics, also strongly influencing the boundary layer stability characteristics. This study investigates the flat plate boundary layer instabilities under high-enthalpy conditions, with a fixed freestream temperature of 2500K and wall temperatures of 300K, 700K, and 1100K. First, the baseflow was computed considering a 5-species air and Park’s two-temperature model. Next the evolution of the instability waves was simulated by employing a harmonic balance approach accounting for non-parallel and high enthalpy. Using Fourier analysis, the dominant instability modes were identified, revealing their spatial growth and frequency characteristics. The stability results show that the change in wall temperature strongly affects the stability characteristics and will increase or decrease the disturbance flow growth depending on the instability mechanism, e.g. first versus second mode waves. Furthermore, the appearance of the supersonic mode can be observed for large wall temperature to edge temperature ratios. In summary, this research provides insight into the mechanisms driving hypersonic boundary layer instability in chemically reacting flows, with important implications on predictive modeling of hypersonic flows and vehicle design.