Droplet collision and jet evolution hydrodynamics in wetting modulated valley configurations

Abstract

Droplet impact hydrodynamics on “V”-shaped valleys or grooves of variant wettability and geometric dimensions have been studied experimentally and probed theoretically. The groove geometry makes the hydrodynamics three-dimensional, as in addition to the droplet dynamics in the lateral direction, liquid jets are generated from the post-impact droplet along the axial direction of the groove. The effect of the impact Weber number (We) on the jet velocity, the non-dimensional spreading width (γ), and north-pole height (h*) has been studied. It has been observed that the inertial forces dominate over the surface forces for higher impact We and hence, the effect of wettability is not important. However, the wettability of the substrate has a significant role in lower impact We as recoiling of the droplet is observed for the impact on the superhydrophobic substrate in this case. It has been observed that the spreading width of the post-impact droplet decreases with the increase in groove steepness. The jetting hydrodynamics has been probed and instantaneously after the impact, the generated jets travel at high velocity, but quickly reduce to a steady value. Jet velocity is observed to increase with an increase in the hydrophobicity of the substrate as well as the impact We. A semi-analytical formalism has been proposed to predict the jet velocity evolution in terms of governing Weber (We) and capillary (Ca) numbers. The predictions from the proposed model are in good agreement with the experimental results.