Interfacial phenomena in impact of droplet array on solid wall

This paper addresses interfacial phenomena associated with droplet array impact on solid surface experimentally, with aid of high-speed photography. Aside from the simultaneous case, droplet array impact is more represented by various non-simultaneous cases, which can be classified into three major subcases: edge/edge interaction with large droplet horizontal spacing, edge/droplet interaction with intermediate droplet spacing, and film/droplet interaction with small spacing. Outcomes include droplet coalescence induced at low velocities and central liquid sheet generated due to droplets interaction at relatively high impact velocities. In quantitative analysis, increasing droplet vertical spacing leads to decreases in both spreading factor and height of central liquid sheet due mainly to increased viscous dissipation. While both the two parameters decrease with increasing droplet horizontal spacing, its effect is weakened with increasing impact velocity, which acts as a positive role for evolution of the two parameters. Although the central sheet continues to descend under gravity at later stage, a sheet height shoulder raises attention because of cusp formation at top of the central sheet. This study provides a fundamental understanding for practical applications involving droplets impingement.