Abstract Recirculation zone dynamics in a cavity located in the bottom wall of a water channel with height h = 0.3 mm and width b = 0.9 mm are investigated experimentally and numerically. A microparticle image velocimetry method and instrumentation are used for the experimental determination of flow velocity distribution and reattachment pattern with Reynolds number from ReDh = 30–2000, cavity length to depth ratios of L/h1 = 10 and 16, and channel expansion ratios of H/h = 1.3, 1.5, 2, 3, and 5. Numerical simulation using commercially available Ansys Fluent software is conducted for analysis of the influence of flow regime and cavity dimensions by changing ReDh, L/h1, and H/h in the ranges of (1–105), (8–36) and (1.25–5), respectively. The experimental and numerical simulation results show that in a laminar flow regime reattachment length increases with increasing ReDh in the same manner as in flow over a backward-facing step. Reh1 and H/h are the main scaling parameters for the reattachment length. However, the results suggest that the transition to a turbulent flow regime occurs earlier due to the small channel spanwise aspect ratio AR = b/h = 3. Reh1 ≈ 500 and Reh1 ≈ 2000 are the critical values that determine the onset of flow transition from a laminar to a turbulent regime and the onset of fully developed turbulent flow, respectively. In addition, it is found that the influence degree of channel expansion ratio depends on whether H/h > 2 or H/h

中文翻译：

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腔体中的再附着长度动力学分析

摘要 对高h = 0.3 mm、宽b = 0.9 mm的水道底壁空腔内的回流带动力学进行了实验和数值研究。微粒图像测速方法和仪器用于实验确定流速分布和重附着模式，雷诺数从 ReDh = 30–2000，腔长与深度比 L/h1 = 10 和 16，以及 H 的通道膨胀比/h = 1.3, 1.5, 2, 3, 和 5. 使用市售 Ansys Fluent 软件进行数值模拟，通过在范围内改变 ReDh、L/h1 和 H/h 来分析流态和腔尺寸的影响分别为 (1-105)、(8-36) 和 (1.25-5)。实验和数值模拟结果表明，在层流流态中，再附着长度随着 ReDh 的增加而增加，其方式与反向台阶上的流动相同。Reh1 和 H/h 是重附着长度的主要缩放参数。然而，结果表明，由于小通道展向纵横比 AR = b/h = 3，向湍流流态的过渡发生得更早。 Reh1 ≈ 500 和 Reh1 ≈ 2000 是确定流动过渡开始的临界值分别是湍流状态的层流和完全发展的湍流的开始。另外发现通道扩张比的影响程度取决于是H/h > 2还是H/h Reh1 和 H/h 是重附着长度的主要缩放参数。然而，结果表明，由于小通道展向纵横比 AR = b/h = 3，向湍流流态的过渡发生得更早。 Reh1 ≈ 500 和 Reh1 ≈ 2000 是确定流动过渡开始的临界值分别是湍流状态的层流和完全发展的湍流的开始。另外发现通道扩张比的影响程度取决于是H/h > 2还是H/h Reh1 和 H/h 是重附着长度的主要缩放参数。然而，结果表明，由于小通道展向纵横比 AR = b/h = 3，向湍流流态的过渡发生得更早。 Reh1 ≈ 500 和 Reh1 ≈ 2000 是确定流动过渡开始的临界值分别是湍流状态的层流和完全发展的湍流的开始。另外发现通道扩张比的影响程度取决于是H/h > 2还是H/h Reh1 ≈ 500 和 Reh1 ≈ 2000 是分别确定从层流到湍流状态的流动过渡开始和完全发展的湍流开始的临界值。另外发现通道扩张比的影响程度取决于是H/h > 2还是H/h Reh1 ≈ 500 和 Reh1 ≈ 2000 是分别确定从层流到湍流状态的流动过渡开始和完全发展的湍流开始的临界值。另外发现通道扩张比的影响程度取决于是H/h > 2还是H/h