微扩散管内幂律流体在不同外电场驱动下非稳态流动数值仿真

Unsteady Flow Numerical Simulation of Power-law Fluids Flowing in the Micro-diffuser Driven by Different Electric Fields

电场驱动下的非牛顿流体在微米级扩散管道内非稳态电渗流动特性是MEMS管设计人员关注的焦点,大部分实际液体可近似为用幂律模型描述的纯粘性流体,所以论文针对幂律流体在有限长微扩散管道内在两种不同形式的外加电场驱动下的非稳态电渗流动情况进行数值仿真.基于Ostwald-De Wael幂律模型和连续介质假说,采用高精度紧致有限差分离散二维完全Poisson-Boltzmann电势方程和Cauchy动量方程,对恒定电场及满足Maxwell方程的电场进行数值仿真,讨论了微扩散管中幂律流体在两种不同外加电场驱动下的瞬时流场分布的差异.结果表明,初始时刻固定扩散角和无量纲壁面电势,无量纲电动宽度的变化对幂律流体电渗流速度分布影响较大;在微扩散管上游等截面处,由恒定电场驱动及Maxwell电场驱动电渗流速度分布差别极小,在扩散管中下游则出现了明显的差别;由恒定电场驱动下的电渗流动在扩散管不同截面下的速度峰值相近,但Maxwell电场诱导的电渗流速度峰值则随管道半径变化出现较大差别.对于外加电场驱动的电渗流动,不同形式的外电场可使流场产生较大差别,而不同性质的流体也会形成不同的流场分布.

Non-newtonian fluids unsteady electroosmosis flow in micro-diffuser is interesting to the MEMS design personnel.And most of the actual liquid is approximate to pure viscous fluid which can be described by power-law model.This paper is in view of the power-law fluids unsteady electroosmosis flow in finite micro-diffuser at two different forms of applied electric fields.Based on Ostwald-De Wael powerlaw model and continuum hypothesis,high accuracy compact difference scheme is used to discrete the twodimensional completely Poisson-Boltzmann and the modified Cauchy momentum equations.Using the numerical method to simulate the power-law fluids electroosmosis flow induced by the constant electric field and the Maxwell electric field,and discusse the difference of instantaneous flow field distribution between the two different applied electric fields.The results show that at the initial time while the diffuser angle and the dimensionless wall potential is fixed,the flow field distribution of power-law fluids are influenced by the change of dimensionless electric width;the difference of velocity profiles between the constant electric field and Maxwell electric field is very small in upstream section,however there is an obvious difference in middle and downstream of diffuser;the speed peak of electroosmosis flow driven by the constant electric field in the different diffuser cross section is close,but it is different to the Maxwell electric field and the induced velocity is change with the pipe radius.For the electroosmosis flow driven by applied electric field,different forms of electric field can make the flow field have great difference,and the different nature of the fluids would form different flow field distribution.