天然水对轴流泵叶轮间隙涡空化的影响研究

The cavitating flow is the key factor responsible to the safe and reliable operation in axial-flow pumps, while the waterborne impurities tends to cause and aggravate the cavitation. Under the condition that the axial-flow pump delivers the natural river water, the water inevitably contains the residues of the aquatic plants. Therefore, the predicted cavitation performance of axial-flow pump basing on the clear water can hardly ensure the cavitation requirement in practical engineering. However, the caivitating flow structure of the pump under the natural water condition is not revealed up to now. This project is designed to focus on the tip region where strong cavitation occurs, to investigate the influence of the water quality on the tip cavitation. The main target is to reveal the affect mechanism of the impurities in the natural water on the vortex cavitation. Then, a new model relating to water quality and vortex will be proposed to supply a reliable tool for the prediction of this kind of cavitation. Combining with the high-speed photography technology, the underlying relation between the water quality and the cavitating vortex flow can be obtained. In addition, the quantitative influence of the water quality on the cavitation characteristics in axial-flow pump can be get through the research on the relation between the degree of the cavitation and the impurity concentration. Finally, the relation between the correction of the net positive suction head and the impurity concentration is constructed to generate effective approach to avoid cavitation and to guide the design of both the axial-flow pump and the pump station.

空化流动是制约轴流泵安全可靠运行的关键因素，水中杂质的存在易诱发空化并加剧空化的严重程度。在轴流泵输送天然河道水的工程背景下，受到水生植物残留物等杂质的影响，基于清水条件预测空化性能的普遍做法已难满足实际水泵的空化安全需求。然而，天然水环境下的轴流泵内部空化流动结构尚不明确。为此，本项目针对轴流泵叶轮内空化严重的间隙区域，开展水质条件对间隙空化的影响研究，以揭示天然水中杂质对间隙涡空化的影响机理为目标，综合旋涡和水质对空化流动的共同影响，提出一套“水质-涡”空化模型，为准确预测水质影响下的空化涡流提供可靠的计算工具。结合高速摄影技术揭示水质特性与空化涡流的内在联系，研究空化程度与杂质浓度的关系，量化水质条件对轴流泵空化性能的影响；构建空化余量修正量与杂质浓度的关系，形成有效的空化防控措施用于指导轴流泵及泵站的工程设计。

空化流动是制约轴流泵安全可靠运行的关键因素，水中杂质的存在易诱发空化并加剧空化的严重程度。基于清水条件预测空化性能的普遍做法已难满足实际水泵的空化安全需求，本项目采用理论分析、实验测试和数值模拟相结合的方法，开展了水质影响下的轴流泵空化流场研究。. 首先，设计加工了水质空化压力测定装置，对比验证了饱和蒸汽压测定装置，测试比较了含不同种类不同浓度杂质水的空化压力特性，补充了杂质水的密度、黏度等属性参数测定，分析了杂质成分和含量对空化压力的影响，构建了一套空化研究所需的水质特性测定装置和研究方法。其次，分别以单水翼绕流和文丘里管内流动为研究对象，开展了清水或非清水的空化实验研究，分析了不同程度的空化流动现象及特征，比较了杂质水对空化流动的影响，研究了考虑水质影响的空化流场数值模拟方法，构建了多因素调控的流动仿真空化模型，揭示了水中杂质和涡流对空化的影响机理。再次，开展了模型轴流泵的空化实验测试，记录了轴流泵叶顶间隙涡空化的动态特征，比较了不同运行工况下的空化现象，分析了轴流泵叶轮内的空化流场形成机理，开展了水质影响下的轴流泵叶顶间隙涡空化的数值模拟研究，拓展了涡流捕捉在其它工程场景中的应用，扩充了流场的湍流特征捕捉和分析，构建了一套叶顶间隙涡空化的预测、辨识和分析方法。最后，考虑水力机械实际工程中的水环境特征，开展了海水背景下的空化流动分析，研究了水体含盐度对空化流动乃至水力机械空化特性的影响，揭示了水中含可溶性杂质成分对空化影响的机理；开展了河水背景下的空化流动分析，研究了水体含固相杂质对空化流动的影响，探索了多相流环境中的流动机理和研究方法。为在非清水环境下确定空化余量和水泵安装高程提供了科学指导。