Dynamic behaviors of droplets impacting on ultrasonically vibrating surfaces

Ultrasonic vibration has a wide application prospect in the fields of droplet atomization and aircraft anti/deicing. The present work experimentally investigates the dynamic behaviors and anti-icing characteristics of droplets, with a wide range of velocities, impacting on ultrasonically vibrating surfaces. Two kinds of splash, mode are observed, including edge splash and surface splash, and a novel rebound mode, named sub-droplet rebound, is found in our experiments. The surface splash is mainly induced by the Faraday instability of surface capillary waves, and the appearance of a large number of bubbles proves that cavitation is also one of the influence factors. By analyzing the interaction of aerodynamic force and surface tension, the critical curve of the edge splash is obtained. The convergence of capillary waves at the apex contributes to the sub-droplet rebound. In addition, the influences of impact velocities and ultrasonic vibration amplitudes on the droplet spreading and the size distribution of secondary droplets are elucidated and discussed. A higher excitation amplitude results in a wider secondary droplet size distribution and a larger average size. We also investigate the dynamic process of supercooled water droplets impacting on ultrasonically vibrating surfaces with and without preformed frozen ice, respectively. The ultrasonic vibration could effectively promote the droplet splash and prevent the ice accumulation even in the state that the surface has been frozen. The anti-icing efficiency of the ultrasonic vibration increases with the increase of the ultrasonic vibration amplitude. The results of this work could provide insights for controlling droplet spreading, atomization, and anti-icing by using ultrasonic vibration.