Oscillation frequency of sessile droplets exposed to shearing gas flows*

Sessile drops exposed to shearing gas flows exhibit intriguing oscillatory motion before being removed from the surface. Our analysis has revealed that this oscillation plays a crucial role in the depinning of droplet contact lines, contributing up to around half of the force required to overcome the adhesion force. This behavior is speculated to be a result of the interplay between surface tension effects and the drag force from the shearing gas flow. The former aims to pin the droplet on the substrate, while the latter seeks to deform the droplet beyond its stable limits, defined by the advancing and receding contact angles. In this study, we evaluated the oscillating frequency of sessile drops under these conditions. Notably, we observed that the oscillating frequency of the droplets increases with the superficial gas velocity of the shearing gas flow. Across the range of flow conditions tested in our experiments, an oscillating frequency of approximately 235 Hz was observed, with 10.76 m/s being one of the tested values for the superficial gas velocity.