Nagalingam Nagaraj, Korede Vikram, Irimia Daniel, Westerweel Jerry, Padding Johan T, Hartkamp Remco, Eral Hüseyin Burak
Process and Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB, Delft, Netherlands.
Sci Rep. 2024 Aug 13;14(1):18763. doi: 10.1038/s41598-024-68971-x.
Oscillatory flow in confined spaces is central to understanding physiological flows and rational design of synthetic periodic-actuation based micromachines. Using theory and experiments on oscillating flows generated through a laser-induced cavitation bubble, we associate the dynamic bubble size (fluid velocity) and bubble lifetime to the laser energy supplied-a control parameter in experiments. Employing different channel cross-section shapes, sizes and lengths, we demonstrate the characteristic scales for velocity, time and energy to depend solely on the channel geometry. Contrary to the generally assumed absence of instability in low Reynolds number flows ( ), we report a momentary flow distortion that originates due to the boundary layer separation near channel walls during flow deceleration. The emergence of distorted laminar states is characterized using two stages. First the conditions for the onset of instabilities is analyzed using the Reynolds number and Womersley number for oscillating flows. Second the growth and the ability of an instability to prevail is analyzed using the convective time scale of the flow. Our findings inform rational design of microsystems leveraging pulsatile flows via cavitation-powered microactuation.
受限空间内的振荡流是理解生理流动以及基于合成周期驱动的微机器合理设计的核心。通过对激光诱导空化气泡产生的振荡流进行理论和实验研究，我们将动态气泡尺寸（流体速度）和气泡寿命与所提供的激光能量联系起来——激光能量是实验中的一个控制参数。通过采用不同的通道横截面形状、尺寸和长度，我们证明了速度、时间和能量的特征尺度仅取决于通道几何形状。与通常认为的低雷诺数流动（ ）中不存在不稳定性相反，我们报告了一种瞬时流动畸变，它是由于流动减速期间通道壁附近的边界层分离而产生的。畸变层流状态的出现分为两个阶段。首先，使用振荡流的雷诺数和沃默斯利数分析不稳定性开始的条件。其次，使用流动的对流时间尺度分析不稳定性的增长及其占主导的能力。我们的研究结果为通过空化驱动微致动利用脉动流的微系统的合理设计提供了依据。
