Numerical Study on the Role of Aerosol Particles in Hypersonic Boundary-Layer Transition

Particle-induced boundary-layer transition is investigated through direct numerical simulation. We examine the receptivity of a hypersonic boundary layer to particles that remain external to the boundary layer as they traverse the post-shock region. This interaction is characteristic of small aerosol particles typically deflected around the vehicle. Particle sizes representing stratospheric aerosols 1 and 10 μm in diameter are considered. An Eulerian–Lagrangian framework was used to simulate the particle momentum and energy coupling to the flowfield. The implementation of the particle model was verified with computational data in the literature for a particle-induced first-mode-dominated wave packet in a Mach 4 wedge flow. The simulations in this paper are performed for a single particle and a 7 deg sharp wedge with freestream conditions representing Mach 7 flight at an altitude of 20 km. The results indicate that a particle can excite an unstable second-mode wave packet without entering the boundary layer. This occurs through the generation of pressure disturbances as the particle enters the shock layer flow.