基于空化冲击能及材料阈值分析的叶片泵空蚀预测研究

Cavitation erosion is produced when the energy contained in a cavity is released and higher than the material threshold strength. Studies of cavitation-erosion mechanism are important to prevent the damage on hydraulic machinery. It is necessary to find a cavitation erosion model with good accuracy for the prediction of the affected region and the material threshold. The potential energy contained in a macro-cavity (cavitation cloud) is transformed into the fluctuation of pressure waves, and further on influence the imploding of micro-scale cavitation structures or single bubbles that are in the vicinity of the hydrofoil surface. Cavitation erosion is not only a small-scale event. To study the multiphysical phenomenon, firstly, video recording by high-speed cameras, acoustic pressure recording by hydrophones, recording of pressure pulsation and material erosion on hydrofoil surface will be obtained synchronously. The impulsive load resulting from the pressure pulsations is a key concept in cavitation erosion. Qualitative measurement of pressure pulsation and cavitation noise are useful information reflecting the magnitude of cavitation damage. Secondly, a new cavitation-erosion model will be proposed to assess the flow aggressiveness, the total affected region and the material plastically deformed. Finally, to validate the model, numerical simulations of unsteady cavitating flows in a centrifugal pump will be carried out. A comparison of new turbulence model is needed to define an appropriate turbulence model, which can be adapted for industrial applications focuses on cavitation erosion prediction. The study provided important theoretical support for cavitation erosion prediction of various engineering applications.

叶片泵无论在航天、海洋工程领域还是在核电、军工等特殊领域都发挥着至关重要的作用，特殊领域中泵空化冲击诱发的叶片断裂会造成重大事故，亟需建立可靠的空蚀预测方法。目前关于空化的研究多为流体单方面的空化形态分析，空化流动对材料破坏的作用机理尚未明晰。空蚀研究是多尺度、多物理场耦合的复杂问题，能量转换过程显著影响施加到材料表面的冲击能量，空泡微观破裂的初始条件由大尺度空化云演化所释放的能量决定。本项目创新地从不同的能量尺度分析空蚀，首先通过多物理场耦合同步测量来分析宏观流动条件对材料微观空蚀的影响规律；然后建立空化冲击能数值计算方法，建立对流尺度、微观尺度耦合作用的能量传递模型，研究对流尺度、微观尺度交界面的动力学行为；最后通过模型泵空蚀试验对所建立的空蚀预测方法进行验证，并修正旋转空化多相湍流模型。基于此预测空蚀的新方法，相关理论和试验研究成果拓展应用到水力机械上的潜力巨大，具有广阔的应用前景。

特殊领域中的高速泵在空化冲击的作用下，叶片断裂会造成重大事故，亟需对其可靠性及抗空蚀性能进行研究。在叶轮的旋转作用下，过流部件近壁面空化流动包含了不同尺度的旋涡运动，空蚀的形成由空泡非定常动力特性及两相间的质量传输过程共同作用。如何构建叶片泵空蚀的数值计算方法是本项目解决的关键问题。本项目结合高速泵过流部件的结构特点，考虑叶轮旋转修正湍流模型，通过泵空蚀试验对高速泵的抗空蚀可靠性进行验证，并建立多尺度耦合的能量传递模型。在确定了空泡溃灭的驱动力和相间传输率两个关键参数后，可以捕捉当地的势能功率密度。使用不同驱动力预测得到的势能功率密度及捕捉到的空蚀源核心区域存在范围和强度的差别。对于离心泵，采用势能功率法预测到的易蚀区较为合理。使用基于奇异值分解的图像时均方法可较好地预测泵内空蚀变化特性。基于压力偏导的空蚀预测结果能较好地匹配实验的空蚀分布情况。相关理论和实验研究成果拓展应用到应急救援领域的潜力巨大，避免特殊领域中叶轮空蚀断裂造成的重大损失或破坏，具有重大意义。