Depinning of water droplets from a horizontal solid surface by wall-bounded shear flows

Liquid droplets depinning due to shear flow aerodynamic loading is relevant to a range of engineering applications. Factors influencing depinning include droplet volume and submergence, shear flow velocity profile and acceleration, and surface wettability. A series of experiments are performed to assess the critical depinning velocity of liquid droplets subjected to an accelerating (i) laminar boundary layer, and (ii) slot jet at varying impingement angles. Critical depinning velocity, cast into a nondimensional critical Weber number, is found to be strongly related to a newly introduced volumetric shape factor, which encapsulates droplet shape and related aspects of substrate wettability.