热态水射流空化强化舰船用泵叶轮的工艺和机理研究

Of special interest is the cavitation damage of the marine pump impeller, which motivates the attempt to strengthen the pump impeller with waterjet cavitation. A combination of experiment and numerical simulation is implemented to explore the mechanism of surface strengthening of the axial-flow impeller. The jet medium temperature is enhanced to lower the threshold of cavitation inception. The entire impeller is strengthened and the rotating state of the impeller is kept during the strengthening process. Along with the variation in medium temperature, jet pressure, jet incident angle, exposure time and rotational speed of the impeller are taken into account as well. Cavitation strengthening effect is assessed through the distributions of microhardness and residual stress over the target surface. The excitation of cavitation bubble collapse is reflected by the transiently acquired pressure fluctuations in the flow field. Surface morphology of the impeller surface is observed with a three-dimensional optical profiling system. A joint application of computational fluid dynamics (CFD) and finite element method (FEM) enables the simulation of jet flow parameter distributions and cavitation. Furthermore, the stress propagation in the impeller and the plastic deformation of the impeller blades are obtained simultaneously. The mechanism of boosting cavitation strengthening effect by hot jet medium is anticipated to be elucidated. The method of evaluating the strengthening effect and surface integrity with respect to the entire impeller is to be built. The influence of multiple parameters on the strengthening effect is to be depicted with a functional relationship. A quantitative correlation is to be constructed between characteristic frequency of pressure fluctuation aroused by cavitation bubble collapse and the local deformation and surface morphological characteristics of the impeller. Current waterjet strengthening theories are anticipated to be supplemented, and surface strengthening technology improved, thereby providing fundamental support to engineering applications of hot-water jet cavitation strengthening.

针对舰船用泵叶轮汽蚀破坏危害严重的问题，探索采用射流空化强化的方法对泵叶轮进行整体强化。借助实验和数值模拟，通过提高射流介质的温度降低空化发生的阈值，对旋转状态的轴流泵叶轮进行强化机理研究。分析介质温度、射流压力、射流入射角度、强化时间和叶轮转速对强化效果的影响；以流场中的瞬时压力脉动检测空化泡溃灭的激励特性；融合计算流体动力学和有限元模拟，模拟射流流动参数分布和空化现象，并同步求解叶轮模型内的应力传播过程及叶片的塑性变形。通过本项目的研究，拟获得介质温度对空化强化效果增强的促进机制；建立评价泵叶轮整体强化效果和表面完整性的方法；形成影响泵叶轮整体强化效果的多元函数关系；解释空化泡溃灭产生的压力脉动特征频率与叶轮的局部变形与表面形貌的定量关系。项目成果补充并完善现有的射流强化理论，拓展表面强化技术，为热态射流空化强化的工程应用提供理论基础。

针对流体机械叶片的空化强化问题，综合运用机理分析、实验研究和数值模拟三种方法，研究了空化作用时间、液体介质温度、液体介质等对空化强化与空蚀的影响，开展了旋转叶轮的空化强化与空蚀实验等研究工作。搭建了3套空化实验装置，构建了CFD-VOF射流空化模拟模型，对实验和模拟结果进行了分析、对比与统计。主要研究结果如下：（1）建立了空化强化效果、空蚀质量损失与空化发生方法、空化作用时间等关键因素之间的关联；描述了塑性变形、空蚀裂纹和组织结构的动态发展过程；（2）获得了不同材质试样在空化泡溃灭作用下的表面特征及力学行为，构建了多方向应力场对表面强化和试样微观组织的影响机制；（3）解释了表面曲率与空化强化与空蚀程度之间的非单调关系，阐明了曲面材料在空化泡溃灭作用下的逐层移去机制；（4）对轴流泵叶片进行空化强化，发现了强化区与空蚀区在叶片表面分布的非对称性，解释了液流与空化泡运动对叶片表面强化的影响；从压力脉动的角度解释了射流空化激励的非定常流动特征；（5）构建了高精度、适应性强的射流空化数值模拟方案，解释了液流与空化泡的相互作用，获得了空化云的演化特征，建立了空化与表面强化的关联；（6）诱发了天然海水中的空化现象，在腐蚀与空化的协同作用下，揭示了材料的强化与空蚀特征，定义了空蚀的特征阶段，解释了钝化膜对空化的抵御作用；（7）突破了曲面空蚀形貌的表征方法，将宏观三维特征与局部形貌相结合，定量地表达截面形态随空化作用时间的变化，获得了均方根粗糙度；（8）拓展了形状记忆合金和复合材料在抗空化空蚀方面的应用，量化了空化对相变温度和组织结构的影响，描述了空化诱发马氏体相变和晶粒细化的机制。.本研究系统地解释了叶片的空化强化与空蚀机理，构建了材料表面形貌与组织结构对空化泡溃灭的响应机制，从能量吸收与转化的角度评价了材料的抗空蚀性能，深化了对液体与空化的联合作用对曲面强化效果影响的理解。