Numerical study on the role of aerosol particles in hypersonic boundary layer transition

Particle-induced 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 that are typically deflected around the vehicle. Particle sizes representative of stratospheric aerosols are considered, namely, 1 and 10 micrometers in diameter. The simulations are performed for a 7-degree sharp wedge with freestream conditions that represent Mach 7 flight at an altitude of 20 km. The results indicate that a particle can excite an unstable second-mode wavepacket without entering the boundary layer. This occurs through the generation of acoustic disturbances as the particle enters the shock layer flow.