超声行波驱动的玻璃表面液滴运动数值模拟

针对液滴铺展和移动的动力学行为在工业生产和微流控芯片等领域有着重要作用,提出了一种基于超声行波理论的弹性体平板驱动模型,利用压电陶瓷的逆压电效应在弹性体玻璃产生超声行波从而驱动液滴运动。借助多物理场软件COMSOL建立液滴模型,首先进行行波分析,验证了驱动液滴的可行性。在0~60 ms中,液滴在超声行波的驱动下进行收缩-铺展的正弦振荡运动。然后通过液滴内部流场结构分析发现,当液滴半径铺展到最大后开始收缩时,液滴与基底接触面处的速度首先发生变化,表明液滴内部速度场的变化对接触线是否发生移动有着重要作用。液滴内部流场存在一个类似于椭圆形的漩涡,说明液滴运动不是单纯由于收缩-铺展而引起的平动,而是滚动着朝前运动。最后分别探讨了液滴移动速度与驱动电压、驱动频率以及动力黏度的关系,结果表明液滴移动速度受动力黏度影响较为显著。

Numerical simulation of droplet motion on glass surface driven by ultrasonic travelling wave

Aimed at the situations of the spreading and moving dynamics behavior of the droplet that plays an important role in industrial production and microfluidic chips,an elastic planar model based on the theory of ultrasonic travelling wave was proposed.The droplet on the elastic glass surface was driven by ultrasonic travelling wave generated by the inverse piezoelectric effect of piezoelectric ceramic.The droplet model was built with multi-physics field software COMSOL.Firstly,through the analysis of the ultrasonic travelling wave,the feasibility of the model was verified.During the period of 0 to 60 ms,the droplet behaves a shrinkingspreading sinusoidal oscillation motion driven by ultrasonic travelling wave.Then,the internal flow structure inside the droplet was also investigated.When the droplet radius spreads to the maximum and begins to shrink,the velocity inside the contact surface between the droplet and the substrate changes first.It shows that the change of the velocity field inside the droplet plays an important role in the motion of the contact line.There is a similar elliptic vortex in the flow field inside the droplet,which illustrates that the droplet motion is not a simple translation induced by shrinking-spreading,but a forward movement with rolling.Finally,we studied the dependency of the moving velocity of the droplet on the parameters (driving voltage,driving frequency and dynamic viscosity) via simulations.The results show that the moving velocity of the droplet is significantly influenced by the dynamic viscosity.