ABSTRACT Hydropower plant units operating in off-design conditions are subject to cavitation flow instabilities, potentially inducing hydro-acoustic resonances under certain conditions. They can be predicted by using one-dimensional numerical models of hydropower plants that rely on a proper modelling of the draft tube cavitation flow in off-design conditions. The latter is based on hydro-acoustic parameters that can be identified experimentally on the reduced scale physical model of the prototype on its complete operating range, which however requires an important number of measurements during model testing to consider the influence of both the head and the discharge. This article proposes a new methodology enabling the prediction of resonance conditions excited by a draft tube cavitation vortex on the complete head range of a hydropower plant unit. The methodology relies on the experimental identification at the model scale of the hydro-acoustic parameters and their transposition from the model to the prototype scale. By expressing the precession frequency of the vortex and the hydro-acoustic parameters of the draft tube cavitation flow as a function of the runner outlet flow swirl number, their value can be predicted on the complete part load operating range of the prototype whatever the value of both the head and discharge. The computation of the first natural frequency with a 1D numerical modelling of the hydropower plant enables finally the prediction of resonance conditions, which are compared with those identified by measurements on the full-scale machine.

中文翻译：

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基于旋流数概念的水力发电厂水声共振预测新方法

摘要 在非设计条件下运行的水电站机组会受到空化流不稳定的影响，在某些条件下可能会引起水声共振。它们可以通过使用水力发电厂的一维数值模型来预测，这些模型依赖于非设计条件下引水管空化流的适当建模。后者基于水声参数，可以在原型的缩小比例物理模型上在其完整的工作范围内通过实验确定，然而，这需要在模型测试期间进行大量的测量，以考虑头部和头部的影响。释放。本文提出了一种新方法，能够预测由水电站机组整个水头范围内的尾管空化涡流激发的共振条件。该方法依赖于水声参数模型尺度的实验识别及其从模型到原型尺度的转换。通过将涡流的进动频率和引流管空化流的水声参数表示为转轮出口流涡流数的函数，它们的值可以在原型的完整部分负载运行范围内进行预测，无论头部和放电。使用水电站的一维数值模型计算第一个自然频率，最终可以预测共振条件，