Dynamics of droplet impact on a superhydrophobic disk

Abstract

An experimental study is performed to investigate the effect of tangential velocity on the dynamics of a water droplet impacting on a spinning superhydrophobic surface. It is revealed that an increase in the tangential velocity results in the spreading of a droplet from symmetrical to asymmetrical shape on the superhydrophobic surface. Moreover, depending on the impact and tangential velocities, three behaviors are observed: bouncing, symmetrical splashing, and asymmetrical splashing. In the bouncing regime, it is found that the droplet contact time is independent of impact velocity and decreases as the tangential velocity increases. However, the maximum spreading diameter in this regime is a function of both the impact and the tangential velocities. Furthermore, a splashing threshold defined as WeRe1/21−kRe−1/2V/U2=K is introduced to estimate the transition between the bouncing, symmetrical splashing, and asymmetrical splashing regimes. It is revealed that the value of K in the present work (i.e., superhydrophobic spinning disk) is approximately 60% less than the K value obtained by other researchers for the case of aluminum spinning disk. Moreover, two values are found for k to define the boundaries between these three observed regimes.