Mehboudi Aryan, Yeom Junghoon
Department of Mechanical Engineering, The University of Texas, Austin, TX, 78758, USA.
Code 6354, Multifunctional Materials Branch, Materials Science and Technology Division, Naval Research Laboratory, Washington, DC, 20375, USA.
Sci Rep. 2021 May 13;11(1):10182. doi: 10.1038/s41598-021-89699-y.
Non-linear effects of the Navier-Stokes equations disappear under the Stokes regime of Newtonian fluid flows disallowing a flow rectification behavior. Here we show that passive flow rectification of Newtonian fluids is obtainable under the Stokes regime of both compressible and incompressible flows by introducing nonlinearity into the otherwise linear Stokes equations. Asymmetric flow resistances arise in shallow nozzle/diffuser microchannels with deformable ceiling, in which the fluid flow is governed by a non-linear coupled fluid-solid mechanics equation. The proposed model captures the unequal deflection profile of the deformable ceiling depending on the flow direction under the identical applied pressure, permitting a larger flow rate in the nozzle configuration. Ultra-low aspect ratio microchannels sealed by a flexible membrane have been fabricated to demonstrate passive flow rectification for low-Reynolds-number flows (0.001 < Re < 10) of common Newtonian fluids such as water, methanol, and isopropyl alcohol. The proposed rectification mechanism is also extended to compressible flows, leading to the first demonstration of rectifying equilibrium gas flows under the Stokes flow regime. While the maximum rectification ratio experimentally obtained in this work is limited to 1.41, a higher value up to 1.76 can be achieved by optimizing the width profile of the asymmetric microchannels.
在牛顿流体流动的斯托克斯 regime 下，纳维 - 斯托克斯方程的非线性效应消失，不允许出现流动整流行为。在此我们表明，通过在原本线性的斯托克斯方程中引入非线性，在可压缩和不可压缩流动的斯托克斯 regime 下都可实现牛顿流体的被动流动整流。在具有可变形顶部的浅喷嘴/扩散器微通道中会出现不对称流动阻力，其中流体流动由非线性耦合流固力学方程控制。所提出的模型捕捉到了在相同施加压力下可变形顶部根据流动方向的不等挠度分布，使得在喷嘴配置中具有更大的流速。已经制造出由柔性膜密封的超低纵横比微通道，以展示水、甲醇和异丙醇等常见牛顿流体在低雷诺数流动（0.001 < Re < 10）下的被动流动整流。所提出的整流机制也扩展到了可压缩流动，首次证明了在斯托克斯流 regime 下对平衡气体流动进行整流。虽然在这项工作中实验获得的最大整流比限于1.41，但通过优化不对称微通道的宽度分布可实现高达1.76的更高值。
