空化流声学模态对水力机械结构动力特性的影响

水力机械发生空化后，流体的声学模态将发生变化并导致结构湿模态变化，同时流体的声学模态被激励时，可能导致结构出现纯声学模态相关的响应。但是目前对空化流声学模态及与之相关的结构湿模态、水力阻尼以及共振响应方面缺乏研究，与之相关的振动问题不能在设计阶段被预测，在水力机械设计运行及故障诊断中存在盲区。为此，本项目拟首先改进单相流体声学模态计算方法，从研究空化对声学模态的影响入手，通过分析声学模态与结构模态在交接面上的耦合和非耦合作用方式，揭示空化流内结构湿模态的转移规律及其机理，给出空化流结构湿模态预测方法；然后利用能量法建立空化流中水力阻尼的计算方法，进而改进声固耦合计算方法，并预测结构在纯声学模态及声-固耦合模态激励下的响应规律及响应机理；最后应用以上方法分析翼型空化、尾水管涡带空化及泵进口回流空化等对转轮湿模态及其结构动力学响应的影响，为保障机组安全稳定运行提供计算方法及指导依据。

Cavitation can change wet modes of submerged structure by changing acoustic modes of the surrounding fluids. Cavitation related acoustic mode can be excited in a submerged structure when exciting mode and frequency is coordinate with it. But because of limited information on the influence of cavitating on the acoustic mode, structure wet mode and related resonance in the field of hydraulic machinery, the related vibration problem might not be correctly predicted in design stage or diagnosed after trouble. This project will focus on this issue. Firstly acoustic mode and of cavitating hydrofoil flow and structure wet mode will be calculated by modified the method used for single phase fluid to study the influence of cavitation parameters on the acoustic mode. Then its effect on structure wet mode and the mechanism of mode transition will be studied by investigate the interaction of acoustic mode and structure mode. The energy method will be modified to predict the hydraulic damping factor. After that the resonance of the structure related with pure acoustic mode and coupling mode be investigated by improved acoustic-structure coupling method. The method will finally be applied to study the acoustic mode ，structure wet mode and resonance characters affected by cavitation on runner blades, draft tube vortex cavitation and back flow cavitation in pump inlet. The study will benefit the design and diagnosis of the hydraulic machinery.