诱导轮空化流动特性实验研究

为了深入研究诱导轮内部的空化流动特性，基于诱导轮空化流动可视化实验台进行了一系列实验，获取了诱导轮的外特性、空化区发展过程以及相应的压力脉动特性。结果表明：流量越大，空化性能曲线越早发生断裂，但存在某个流量使诱导轮具备最佳空化性能；随着空化数的降低，空化首先发生于泄漏涡中，泄漏涡空化逐渐与泄漏流中的剪切层空化连成一片，形成稳定的泄漏空化区，流量越小，空化区面积越大，叶尖的压力脉动幅值也随着空化区面积增大而升高，由于空化区对称分布，压力脉动由叶片通过频率主导；进一步降低空化数时，开始出现各类空化不稳定现象，小流量下出现明显的回流涡空化，大流量下出现同步旋转空化，后者会引起大幅的压力振荡，同时会导致扬程部分下降。空化区进一步发展，导致大流量下发生低频轴向流动不稳定现象，空化喘振。空化区发展至叶轮出口时，影响出口液流角，诱导轮完全失去作功能力，发生空化性能断裂。

Experiment of Cavitating Flow Characteristics of Inducer

Aiming to obtain deep insight into the cavitating flow characteristics inside an inducer, a series of experiments were performed to achieve the inducer macroscopic performance, cavitation development and the corresponding pressure fluctuation characteristics. It was found that the breakdown occurred earlier at larger flow coefficient, but there was one flow coefficient at which the inducer had the best cavitation performance. As the cavitation number decreased, the cavities occurred in the leakage vortex firstly, and the leakage vortex cavitation was connected with the shear cavitation in the leakage flow, forming a stable leakage cavitation. And the size of cavitation area was larger at smaller flow coefficients. The amplitude of pressure fluctuation near the tip was increased with the increase of cavitation area, and the blade passing frequency was the dominant frequency as the cavities were distributed symmetrically. As the cavitation number decreased further, several cavitation instabilities occurred, such as the backflow vortex cavitation and synchronous rotating cavitation, which would induce large amplitude pressure vibration and head degradation partially. The former one was developed from the leakage cavitation under heavy blade loading conditions, the later one was attributed to the unsymmetrical cavities without propagating in the circumference direction. With cavitation further development, axial flow instability occurred at larger flow coefficients, which was corresponding to the cavitation surge, and caused by the synchronous variation of the cavities on the three blades. When the cavities were stretched to the outlet of the inducer, the outlet flow angles were affected, the inducer lost the work ability, and cavitation breakdown occurred.