ID 107

Aerodynamically driven drop propagation and breakup on a solid substrate

 

Abstract:

Aerodynamically driven drop motion and breakup are relevant for many fields, e.g. process engineering, printing, ice accretion, car soiling and exterior water management on vehicles. Different phenomena are observed when a liquid drop is placed on a solid substrate exposed to a strong gas cross-flow: drop oscillations, incipient motion and propagation, coalescence with neighboring drops, drop breakup and splash. These phenomena are governed mainly by the pressure induced by the gas flow, by surface tension and the forces associated with the substrate contact angle hysteresis.

In this experimental and theoretical study aerodynamically driven drop behavior is investigated in a fully turbulent, two-dimensional channel flow. The behavior of water drops on different surfaces with varying contact angle hysteresis and at different air flow velocities is observed using high-speed video. The experiments show that the aerodynamic drag is a function not of the Reynolds number but mainly of the aerodynamic Weber number, based on the characteristic airflow velocity measured in the vicinity of the drop. This dependence is associated with the drop deformation. A theoretical model is developed which predicts the drop propagation velocity and a threshold for drop breakup.