Air-water flows occur commonly in stepped spillways including the nappe flow regime for low flow rates. The present laboratory experiments researched the nappe flow regime in a stepped chute with prototype-scale steps height providing unique insights into the evolution of nappe flows along a stepped chute. Detailed visual observations highlighted the varying flow features along the stepped chute including the evolution of flow aeration, of jet properties and of instationarities in form of jump waves and cavity fluctuations with typical frequencies of around 1 Hz. These instationarities were caused by complex flow interactions at the impingement of the jet on the horizontal step face. Detailed air-water flow measurements revealed the complexity of the flows highlighting both S-shape and jet-like void fraction distributions and jet-like interfacial velocity distributions downstream of the jet impact and at step edges. This resulted in a downwards shift of the bubble count rate distributions closer to the step face. The nappe flows showed strong energy dissipation and reaeration performances along the stepped chute. The present study provided a robust and extensive characterisation of nappe flows and due to the large scale of the experiments, the results should provide confidence for the design of stepped chutes with embankment dam slope.

空气-水流通常出现在阶梯式溢洪道中，包括用于低流速的推覆式水流方案。当前的实验室实验研究了阶梯形斜槽中的尿布流动状态，原型尺寸为台阶高度，为沿阶梯形斜槽的尿布流动演变提供了独特的见解。详细的视觉观察突出了沿阶梯状滑槽的各种流动特征，包括通气，射流特性和平稳状态的演变，其形式为跳跃波和腔波动，典型频率约为1 Hz。这些不平稳性是由于在水平阶梯面上的射流撞击时复杂的流动相互作用引起的。详细的空气-水流量测量揭示了流量的复杂性，突出了S形和射流状空隙分数分布以及射流冲击下游和台阶边缘处的射流状界面速度分布。这导致气泡计数速率分布向下移动更靠近阶梯面。尿布流沿阶梯状滑道表现出较强的能量消散和净化性能。本研究提供了一个健壮和广泛的推覆流特征，由于实验规模大，结果应为堤坝坝坡阶跃溜槽的设计提供信心。尿布流沿阶梯状滑道表现出较强的能量消散和净化性能。本研究提供了一个健壮和广泛的推覆流特征，由于实验规模大，结果应为堤坝坝坡阶跃溜槽的设计提供信心。尿布流沿阶梯状滑道表现出较强的能量消散和净化性能。本研究提供了一个健壮和广泛的推覆流特征，由于实验规模大，结果应为堤坝坝坡阶跃溜槽的设计提供信心。