用于电动微流体计算模拟的自由界面重构技术比较

Comparison of VOF Free Interface Reconstruction Tracking Techniques for Simulation of Electrokinetic Microfluidics

摘要: 电动微流体是微全分析系统中样品输运的主要形式，数值模拟是计算和分析电动微流体样品输运特性的重要手段。由于微通道中区带样品在流体内存在大浓度梯度的界面，在计算时很容易引起数值耗散，对计算精度影响严重。本文探讨了电动微流体样品输运计算中数值耗散的产生原因和消除措施，利用有限体积法求解电场分布和流场分布，在此基础上应用自由界面重构技术对数值流向量进行了处理并求解微通道中样品传输，有效消除了界面处数值耗散的影响，并给出微通道中电泳分离和电致混合增强的计算模拟结果，研究结果表明：采用FCT-VOF和基于积分平均型TVD格式的VOF方法对上述算例的样品界面进行重构，能够保持界面平滑的同时，有效抑制了数值耗散，获得较好的计算精度。

Abstract: Electrokinetic microfluidics is one of the main subcategories for sample transport in Micro-Total- Analysis-System. Numerical simulation is an efficient method for calculating and analyzing trans- port properties of samples in electrokinetic microfluidics. However, since the strong discontinuity exists at the interface of sample zone, the numerical dissipation near the interface becomes a key problem that can seriously influence the computational accuracy. In this paper, the reasons of numerical dissipation are theoretically analyzed and the techniques based on free interface reconstruction are provided to weaken the numerical dissipation. Firstly, the electric field and the flow field are solved by using the finite volume method. Then, in order to constraint the numerical dissipation, several techniques based on the volume of fluid (VOF) are utilized to reconstruct the flow vectors and solve the sample transport. Lastly, with the developed algorithm, capillary electrophoresis and electrokinetically driven enhanced mixing in microchannels are simulated. The results show that both FCT-VOF and TVD-VOF can significantly constraint the numerical dissipation while keeping the interface smoothing and are suitable for the simulation of electrokinetic microfluidics and other applications.