Transition flow regime on stepped spillways: air–water flow characteristics and step-cavity fluctuations
Transition flow regime on stepped spillways: air–water flow characteristics and step-cavity fluctuations
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DOI：
10.1007/s10652-018-9575-y
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发表时间：
2018-01
影响因子：
2.2
通讯作者：
M. Kramer;H. Chanson
中科院分区：
文献类型：
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作者：
M. Kramer;H. Chanson
阶梯式溢洪道是人造水工结构，旨在控制流量的释放并实现高能量耗散。给定的阶梯式溜槽几何形状的流动模式可以分为不同的状态。这里，过渡流态发生在一系列中间排放处，其特征是强烈的水动力波动和自由表面附近的强烈飞溅。迄今为止，只有很少的实验数据可用于过渡流。由于这种流态很可能发生在为撇流操作而设计的阶梯式溢洪道上，因此了解过渡流特性对于确保安全操作非常重要。本文研究了实验室溢洪道过渡流态的水力学，详细描述了空气-水流特性，并对连续阶梯腔内的水池深度波动进行了基于图像的分析。结果显示了两种不同的空隙率和湍流强度分布，表明存在上部和下部过渡流动子区域。基于图像的分析表明，两个子状态的起始点下游都存在快速且逐渐变化的流动区域，而物理模型中并未达到完全平衡流动。总体而言，该研究通过组装不同两相流参数（包括空隙率、界面速度和阶梯腔池高度）的解析解，有助于改善过渡流的表征。
Stepped spillways are man-made hydraulic structures designed to control the release of flow and to achieve a high energy dissipation. The flow pattern for a given stepped chute geometry can be distinguished into different regimes. Herein, the transition flow regime occurs at a range of intermediate discharges and is characterised by strong hydrodynamic fluctuations and intense splashing next to the free-surface. Up to date, only minimal experimental data is available for the transition flow. As this flow regime is likely to occur on stepped spillways designed for skimming flow operation, a knowledge of the transition flow characteristics is important to ensure safe operation. The present article investigates the hydraulics of the transition flow regime on a laboratory spillway, presenting a detailed characterisation of air–water flow properties and an image-based analysis of pool depth fluctuations within successive step-cavities. The results show two different void fraction and turbulence intensity profiles, indicating the existence of an upper and a lower transition flow sub-regime. The image-based analysis suggests the presence of a rapidly and a gradually varied flow region downstream of the inception point for both sub-regimes, whereas full equilibrium flow was not reached in the physical model. Overall, the study contributes towards improving the characterisation of the transition flow by assembling analytical solutions for different two-phase flow parameters, including void fraction, interfacial velocity and step-cavity pool height.