Abstract The actual requirements of the energy market enforce the hydraulic turbine to operate far from the best efficiency point. When hydraulic turbines operate at partial discharge, downstream of the runner (in the conical diffuser), the decelerated swirling flow becomes highly unstable. In these conditions a spiral vortex breakdown occurs, also known in engineering literature as the precessing vortex rope. The flow unsteadiness produced by the vortex rope results in severe pressure fluctuations that hinder the turbine operation or may cause accidents. We propose the water jet method for decelerated swirling flow with vortex rope from conical diffuser to mitigate the unsteadiness. The method involves injecting water at the inlet of the conical diffuser. Initial experimental investigations of the unsteady pressure field at conical diffuser wall reveal that the water injection method mitigates the pressure pulsations associated to the precessing vortex rope. In this paper, we investigate experimental measurements of the unsteady velocity field in a conical diffuser using LDA (Laser Doppler Anemometry). The main goal of the paper is to show how different water-jet discharge rates change the velocity field and the characteristics of the vortex rope in the wake.

中文翻译：

---

基于喷水控制法的锥形扩压器旋流实验研究

摘要 能源市场的实际需求迫使水轮机远离最佳效率点运行。当水轮机在部分排放下运行时，在转轮下游（在锥形扩压器中），减速的涡流变得非常不稳定。在这些条件下，会发生螺旋涡旋破裂，在工程文献中也称为进动涡旋绳。涡绳产生的流动不稳定性导致严重的压力波动，阻碍涡轮机运行或可能导致事故。我们提出了使用锥形扩散器的涡绳减速涡流的水射流方法，以减轻不稳定性。该方法包括在锥形扩散器的入口处注入水。锥形扩压器壁处不稳定压力场的初步实验研究表明，注水方法减轻了与进动涡绳相关的压力脉动。在本文中，我们使用 LDA（激光多普勒风速测量法）研究了锥形扩散器中非定常速度场的实验测量。该论文的主要目标是展示不同的水射流排放速率如何改变尾流中的速度场和涡绳特性。