畸变入流条件下离心泵内部流动机理及其压力脉动特性研究

Distortion inflow that caused by the inflow pipe, inlet reverse flow and pre-whirl was usually found at the entrance of centrifugal pump in engineering operation. Thus a Contradictions between the uniform inflow in pump design and distortion inflow in engineering operation was brought out. Based on the LDV and PIV experimental technology, the fluid at the entrance of the centrifugal impeller and fluid in the pump would be experimental test in this project. The precision and simulation efficiency of existing large-eddy simulations method is not high. Therefore, an adaptive method for solving the average mixing length in sub-grid stress model would be developed to improve the efficiency and precision of LES method. By means of this new model, the fluid flow with strong anisotropy turbulence in hydraulic machinery can be accurately simulated. On the basis of experimental tests and numerical simulation, the mechanism of the distortion inflow conditions within the centrifugal pump and the pressure characteristics would be studied. The mechanism of the interaction of different scales of vortex exiting in the inflow region would be clarified.The exciting force on the blade of centrifugal impeller and the pressure fluctuation characteristics of the pump suffered from the distortion unsteady inflow conditions would be analyzed. The relational model between the distortion inflow and the unsteady excitation force and pressure characteristics would be finally established to lay the theoretical basis of the internal flow in order to improve the security and stability of the centrifugal pump in engineering operation.

实际运行中的离心泵入口存在由管路、进口回流及预旋而引起的畸变入流，从而导致了离心泵"设计过程中的均匀入流"和"实际运行中的畸变入流"之间的矛盾。本项目拟利用PIV和LDV对畸变入流条件下叶轮入口及离心泵的内部流动进行详细实验测试，同时借助数值模拟的优势，针对现有大涡模拟方法预示精度不足与模拟效率不高的缺陷，开发自适应求解平均混合长度的亚格子应力模型，提高大涡模拟方法对于水力机械内强各向异性湍流的模拟精度与效率。在实验测试和数值模拟的基础上对不同畸变入流条件下的离心泵内部流动机理和压力脉动特性进行研究，阐明入流区内各种不同尺度的漩涡与叶轮相互作用的机制，揭示不同涡团在旋转叶轮内的流动、发展、形成新的漩涡的规律；分析畸变入流条件下叶片所受的非定常激振力和压力脉动特征；建立畸变入流对叶片所受非定常激振力和压力脉动特性影响的关联模型，为提高离心泵在实际运行中的安全稳定性奠定内流理论基础。

在实际运行中，离心泵入口存在由管路、进口回流及预旋而引起的畸变入流，从而导致离心泵“初始设计的均匀入流”和“实际运行中的畸变入流”之间的矛盾。本项目利用数值模拟的方法对由进口弯道所引起的剪切流、预旋、回流等不同因素所引起的入口畸变的机理和流动特性进行了研究，针对水力机械内的强各向异性湍流，研究了适合叶轮机械的数值模型。对离心泵内由于流动畸变而引起的诱导轮和叶轮、诱导轮和扩压器叶片以及多级离心泵内不同级叶轮之间的时序的影响进行了研究，同时研究了轴流泵前后导叶之间的时序效应。对离心泵叶轮入口处的流动进行了PIV实验测试，探讨了进口预旋对叶轮内部流动的影响。对不同工况下离心泵的压力脉动特性进行了研究，发现叶片数不同时压力脉动特性呈现明显的不同，通过与数值模拟结果的对比探讨了不同叶片数叶轮内部的流动特性。项目还开展了固液两相流环境下叶片磨蚀特性研究，对在不同入流条件下叶片的磨蚀特性进行实验测试，从材料本身的角度探讨水力机械的磨蚀机理。利用实验测试的方法探讨轴端密封附近的回流问题，对密封间隙内的流动进行了研究。在此基础上，针对入流畸变情况下水力机械的过渡过程、表面粗糙度对水力机械性能的影响等进行了研究。项目成果对于提高水力机械特别是离心泵实际运行中的安全稳定性奠定了内流理论分析基础，为设计和制造高效率、高抗磨蚀性能水力机械提供了数据支撑。