Role of Inertial Force and Dynamic Contact Angle on the Incipient Motion of Droplets in Shearing Gas Flow

This study experimentally investigates the oscillatory dynamics of wind-driven droplets using high-speed imaging to capture droplet profiles within the symmetry plane and to characterize their natural oscillation frequencies. Results reveal that the eigenfrequencies vary spatially due to distinct oscillation modes occurring at different droplet locations. Notably, the fundamental eigenfrequency decreases with reducing droplet volume, while droplet viscosity exerts minimal influence on this frequency. Prior to the onset of motion, the dynamic contact angle consistently remains between the advancing and receding angles. The inertial forces generated by droplet oscillation are found to be significantly greater than the adhesion forces, indicating that classical static models are inadequate for capturing inertial contributions to droplet motion. These findings offer new insights into the role of oscillatory behavior in influencing the dynamics of droplet motion, and contribute to a more detailed understanding of wind-driven droplet transport phenomena.