近失速工况下混流泵轮缘泄漏流的动力学行为及失稳机制

Flow instability induced by tip leakage flow of mixed-flow pump has become one of the urgent scientific problems needed to solve in the defense equipment and the large-scale hydraulic projects. The dynamics behavior study of leakage flow is the basic study to explore and suppress the flow instability. The project starts from the exploring of the physical characteristics of tip gap flow field in the mixed-flow pump, to study the unsteady flow characteristics and instability mechanism of leakage flow. The flow morphology and microstructure of tip leakage flow will be studied by high-speed photography, 3D-PIV measurements and numerical methods, to reveal the vortex rolled suction effects and the temporal evolution of birth, development and broken process. Based on dynamic pressure measurement, the unsteady characteristics and circumferential propagation characteristics of near-stall transition flow field will be studied, to reveal the self-excited unsteady incentives and mechanisms, and to clarify the internal relations of spatial structure and temporal characteristics. By defining the flow characteristic parameters, vortex core trajectories are presented by swirling strength method, to find the characterization interface structure of instability flow and the transition critical flow coefficient. The rotating stall criterion triggered by flow dynamics behavior will be established, and the effective method to suppress stall will be proposed. This project aims to reveal the true physical essence of leakage flow in mixed-flow pump, to grasp the instability mechanism triggered by dynamic behavior, and to provide a theoretical basis to suppress or weaken its adverse effects.

混流泵轮缘泄漏流诱发流动失稳已成为国防装备和大型水利工程急需解决的关键科学问题之一，研究泄漏流的动力学行为是探索流动失稳机制并抑制失速发生的基础研究。本项目从探索混流泵轮缘间隙流场的物理特性出发，研究泄漏流的非定常特性及失稳机制。基于高速摄影、3D-PIV测量和数值方法研究轮缘泄漏流的微观结构和形貌特征，揭示泄漏涡的卷吸效应以及初生、发展、破碎的时空演变过程；基于动态压力测量，探索近失速转捩流场、失速流场泄漏流时间非定常特征以及周向传播特性，揭示泄漏流自激非定常性的诱因和机理，阐明泄漏流空间结构与时间特征的内在联系；定义流动特征参数，采用漩涡强度法辨识涡核运动轨迹，寻找表征流场失稳的特征界面结构和转捩临界流量系数，建立泄漏流动力学行为触发旋转失速的判断准则并提出有效的抑制方法。本项目研究旨在揭示混流泵泄漏流的真实物理本质，掌握动力学行为触发流动失稳机制，为抑制或消弱其不良影响提供理论依据。

混流泵轮缘泄漏流诱发流动失稳已成为国防装备和大型水利工程急需解决的关键科学问题之一，研究泄漏流的动力学行为是探索流动失稳机制并抑制失速发生的基础研究。本项目从探索混流泵轮缘间隙流场的物理特性出发，研究泄漏流的非定常特性及失稳机制。基于PIV测量和SST k-ω湍流模型的数值方法研究了不同轮缘间隙下混流泵的泄漏量和泄漏流的形态，解析了不同轮缘间隙下泄漏涡的空间结构和流态特征，精细刻画了轮缘泄漏涡特征间隙尺度下的形态演化，建立了泄漏流典型表现的三维空间结构模型。基于动态压力测量和高精度数值计算，研究了叶轮进口、中部和出口处轮缘区域不同监测点压力脉动的时域和频域响应，获取近失速工况点轮缘区流场非定常性的特征频率、幅值分布和瞬态流场特征，阐明轮缘泄漏流空间结构与时间特征的内在联系。采用熵产分析方法对混流泵近失速流场中高能量损失区域进行可视化，基于Q准则识别叶轮内多尺度涡结构，建立混流泵能量特性与轮缘间隙尺度的映射函数关系。关联流场速度分布、涡量分布以及三维轮缘泄漏流流态，掌握不同时刻轮缘泄漏流、失速涡动态演化以及相互作用机制，解析单流道失速核初生、发展、溃灭演化过程，揭示轮缘流动畸变诱导预失速及叶尖初生失速产生的机理，建立泄漏流非定常流动行为触发旋转失速的判断准则。.项目研究具有较高的理论意义和学术价值，具有广阔应用前景。研究成果不仅可以加深人们对水力机械中轮缘泄漏流非定常特性的认知、丰富旋转失速理论，而且可以为大型水力机械的扩稳控制和稳定性设计提供理论依据。