Numerical simulation of modal evolution and flow field structure of vibrating droplets on hydrophobic surface

Abstract

In order to understand the evolution and flow structure within vertical vibrating droplets on hydrophobic surfaces, a three-dimensional model of the vibrating droplet is developed, and the dynamic contact angle of the vibrating droplet is considered. The numerical simulations are performed for the droplet attached to the vertical vibrating plane by the VOF-CSF method, and the four resonance modes of the droplets are obtained. The evolution of modes (2, 4, 6, and 8), internal flow structures and the variation of the dynamic contact angle are predicted. With the change of the vibration acceleration, the droplet can express a wealth of modes, and the specific mode depends on the frequency of the vibrating acceleration. Based on this model, in this paper the internal flow field structure of the droplet is further analyzed. In mode 2 and mode 4, a Y-shaped flow is generated from the bottom of the droplet, while in mode 6 and mode 8, there is a symmetrical eddy flow. And the higher the order of the resonance mode, the larger the average value of the internal velocity of the droplet is. The dynamic contact angle of the vibrating droplet obviously deviates from the static contact angle, indicating the necessity to consider the dynamic contact angle in simulating the vertical vibrating of droplet. The simulation results are compared with the experimental results from the literature, showing that they are in good agreement with each other.