From low velocity droplet impact to high velocity particle impact

Kurzfassung

Fluid dynamic processes occurring during the impact of a droplet onto the surface of a pool are surveyed. First, phenomena characteristic of low velocity impacts such as the formation of vortex rings, the importance of capillarity, bubble entrainment and jetting are considered. Furthermore, a connection between critical conditions of bubble entrainment by drop impact and critical conditions of the inception of self-entrainment of high-velocity turbulent open-channel flows will be addressed. Compressibility effects that become dominant at high impact velocities are considered next. After impact, pressure waves propagating within the droplet may result in the formation of cavitation bubbles. The inception of cavitation is modelled by a microbubble model. At very high velocities the resulting high impact pressures can cause impinging solid metal particles to stick to a metal surface. This is exploited in the cold spray coating process. Finally, the emission of light that is sometimes observed when metallic particles impinge on a metal plate with a high velocity is traced to mechanoluminescence.