  The evolution of multi-mode instabilities in a hypersonic boundary layer and
their effects on aerodynamic heating are investigated. Experiments are
conducted in a Mach 6 wind tunnel using Rayleigh-scattering flow visualization,
fast-response pressure sensors, fluorescent temperature-sensitive paint (TSP),
and particle image velocimetry (PIV). Calculations are also performed based on
both parabolized stability equations (PSE) and direct numerical simulations
(DNS). It is found that second-mode dilatational waves, accompanied by
high-frequency alternating fluid compression and expansion, produce intense
aerodynamic heating in a small region that rapidly heats the fluid passing
through it. As a result, the surface temperature rapidly increases and results
in an overshoot over the nominal transitional value. When the dilatation waves
decay downstream, the surface temperature decreases gradually until transition
is completed. A theoretical analysis is provided to interpret the temperature
distribution affected by the aerodynamic heating.
