Tai Jiayan, Lam Yee Cheong
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
Micromachines (Basel). 2019 Feb 7;10(2):110. doi: 10.3390/mi10020110.
Viscous liquid flow in micro-channels is typically laminar because of the low Reynolds number constraint. However, by introducing elasticity into the fluids, the flow behavior could change drastically to become turbulent; this elasticity can be realized by dissolving small quantities of polymer molecules into an aqueous solvent. Our recent investigation has directly visualized the extension and relaxation of these polymer molecules in an aqueous solution. This elastic-driven phenomenon is known as 'elastic turbulence'. Hitherto, existing studies on elastic flow instability are mostly limited to single-stream flows, and a comprehensive statistical analysis of a multi-stream elastic turbulent micro-channel flow is needed to provide additional physical understanding. Here, we investigate the flow field characteristics of elastic turbulence in a 3-stream contraction-expansion micro-channel flow. By applying statistical analyses and flow visualization tools, we show that the flow field bares many similarities to that of inertia-driven turbulence. More interestingly, we observed regions with two different types of power-law dependence in the velocity power spectra at high frequencies. This is a typical characteristic of two-dimensional turbulence and has hitherto not been reported for elastic turbulent micro-channel flows.
由于雷诺数较低的限制，微通道中的粘性液体流动通常为层流。然而，通过向流体中引入弹性，流动行为可能会急剧变化，变为湍流；这种弹性可以通过将少量聚合物分子溶解在水性溶剂中来实现。我们最近的研究直接观察到了这些聚合物分子在水溶液中的伸展和松弛。这种由弹性驱动的现象被称为“弹性湍流”。迄今为止，现有的关于弹性流动不稳定性的研究大多局限于单股流，需要对多股流弹性湍流微通道流动进行全面的统计分析，以提供更多的物理理解。在此，我们研究了三股流收缩-扩张微通道流动中弹性湍流的流场特性。通过应用统计分析和流动可视化工具，我们表明该流场与惯性驱动湍流的流场有许多相似之处。更有趣的是，我们在高频速度功率谱中观察到了具有两种不同类型幂律依赖性的区域。这是二维湍流的典型特征，迄今为止尚未在弹性湍流微通道流动中报道过。
