Particle approach to a stagnation point at a wall: Viscous damping and collision dynamics

A particle carried by a wall-normal flow can get critically close to the wall, depending on the particle radius compared with the flow boundary-layer thickness, on the surface effective roughness, and on the particle-to-fluid density ratio. At sufficiently large inertia, the particle bounces back. The rebound velocity of a neutrally buoyant particle at the stagnation point at the wall is examined. The rebound height of a particle pair approaching the stagnation point is surprisingly large compared with that of single particle.