多级孔板泄洪洞水流空化特性

多级孔板泄洪洞是一种利用水流强剪切混掺而实现消能的内消能工形式，而抗空化空蚀性能是影响多级孔板泄洪洞安全运行的重要指标之一。本文以小浪底1号孔板泄洪洞为例，在水力学原型观测资料的基础上系统分析了多级孔板泄洪洞的空化特性，并结合几何比尺为1:40的减压模型试验资料分析了缩尺效应对初生空化数的影响。结果表明：水流空化数对库水位的变化不敏感，而初生空化数则随着库水位的升高而增大，受此影响，库水位越高时各级孔板发生空化水流对应的闸门开度越小；缩尺效应对多级孔板泄洪洞初生空化具有显著影响，经模型试验测得的初生空化数须进行缩尺效应修正；对于多级孔板泄洪洞，其结构尺寸和水流流速是影响初生空化数的主要参数，基于此提出了减压试验初生空化数的缩尺效应修正方法，经与原型观测资料对比，误差小于2%。相关成果利于深化对多级孔板泄洪洞水力特性的认识，有助于多级孔板泄洪洞的推广应用。

Cavitation characteristics of flows in multi-orifice spillway tunnel

The multi-stage orifice spillway tunnel is a type of internal energy dissipator that realizes energy dissipation through strong shear mixing of water flow, and its cavitation resisting performance is a key index affecting the safety of its operation. This paper presents a systematic analysis of the cavitation characteristics of the flows in a multi-stage orifice plate spillway tunnel based on the prototype hydraulic observation data of the spillway tunnel No.1 of the Xiaolangdi Dam, and examines the influence of scale effect on the incipient cavitation number by comparing with the measurements on our 1:40 vacuum tank model. The results show that the flow cavitation number is insensitive to changes in the reservoir water stage, while the incipient cavitation number increases with a rising stage. Consequently, a higher reservoir stage will lead to a smaller gate opening threshold of incipient cavitation. For a multi-stage orifice spillway tunnel, its incipient cavitation number is significantly influenced by scale effect; thus, the value obtained from a scale model must be modified. And its structure size and flow velocity are the main factors affecting the incipient cavitation number. Based on this, we work out a new method for correcting the incipient cavitation number of a vacuum tank model, achieving an error less than 2% against the prototype data and thus deepening our understanding of multi-stage orifice spillway tunnel hydraulics.