疏水表面振动液滴模态演化与流场结构的数值模拟

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

为了研究疏水表面垂直振动液滴的运动规律,本文建立了振动液滴的三维模型,考虑了振动液滴的动态接触角变化过程,通过流体体积函数和连续表面张力(volume of fluid-continue surface force,VOF-CSF)方法实现了液滴受迫振动的数值模拟,得到了液滴的四种模态(2,4,6和8)动态演化过程、内部流场结构以及动态接触角的变化规律.随着振动加速度的改变,液滴可表现出丰富的模态,而具体模态依赖于振动加速度的频率变化.以此为基础,本文对液滴的内部流场结构做了进一步的分析.在模态2和模态4时,液滴内部流动从底部向上产生“Y”型流动,而在模态6和模态8时呈现对称的涡流动.且共振模态阶数越高,液滴内部速度平均值越大.液滴振动时的动态接触角明显偏离静态接触角,表明液滴振动模型有必要考虑动态接触角.模拟结果与文献中的实验结果做了对比,结果符合良好.

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.