Department of Mathematics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
Department of Mathematics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
Philos Trans A Math Phys Eng Sci. 2014 Jul 28;372(2020). doi: 10.1098/rsta.2014.0066.
We investigate electrostatically induced interfacial instabilities and subsequent generation of nonlinear coherent structures in immiscible, viscous, dielectric multi-layer stratified flows confined in small-scale channels. Vertical electric fields are imposed across the channel to produce interfacial instabilities that would normally be absent in such flows. In situations when the imposed vertical fields are constant, interfacial instabilities emerge due to the presence of electrostatic forces, and we follow the nonlinear dynamics via direct numerical simulations. We also propose and illustrate a novel pumping mechanism in microfluidic devices that does not use moving parts. This is achieved by first inducing interfacial instabilities using constant background electric fields to obtain fully nonlinear deformations. The second step involves the manipulation of the imposed voltage on the lower electrode (channel wall) to produce a spatio-temporally varying voltage there, in the form of a travelling wave with pre-determined properties. Such travelling wave dielectrophoresis methods are shown to generate intricate fluid-surface-structure interactions that can be of practical value since they produce net mass flux along the channel and thus are candidates for microfluidic pumps without moving parts. We show via extensive direct numerical simulations that this pumping phenomenon is a result of an externally induced nonlinear travelling wave that forms at the fluid-fluid interface and study the characteristics of the generated velocity field inside the channel.
我们研究了在受限于小尺度通道中的不混溶、粘性、介电多层分层流中静电感应界面不稳定性以及随后产生的非线性相干结构。垂直电场被施加到通道中以产生通常在这种流动中不存在的界面不稳定性。在施加的垂直场恒定的情况下，由于静电力的存在，界面不稳定性会出现，我们通过直接数值模拟来跟踪非线性动力学。我们还提出并说明了一种新颖的微流控器件中的泵送机制，该机制不使用运动部件。这是通过首先使用恒定的背景电场来诱导界面不稳定性来实现的，以获得完全非线性的变形。第二步涉及对下电极（通道壁）上施加的电压进行操纵，以在那里产生具有预定特性的行波形式的时变电压。这种行波介电泳方法被证明可以产生复杂的流体-表面-结构相互作用，这可能具有实际价值，因为它们沿着通道产生净质量通量，因此是无运动部件的微流泵的候选者。我们通过广泛的直接数值模拟表明，这种泵送现象是在流体-流体界面处形成的外部感应非线性行波的结果，并研究了通道内部产生的速度场的特征。
