导叶式离心泵内部旋转失速的产生机理及其特性研究

Rotating stall is a common unstable flow phenomenon in centrifugal pumps, usually occurring in part-load conditions. Rotating stall will cause performance instability when the pump is running, and even excite the resonance of the whole pump system in some extreme cases. In this research, high-precision three-dimensional time-resolved particle image velocimetry (TR-PIV) and micro high-frequency pressure transducers will be applied to measure the internal flow fields in the impeller and diffuser region of the pump before and after rotating stall occurs. Furthermore, a simple and efficient sub-grid scale model will be developed to overcome the drawbacks of low precision and low simulation efficiency in traditional models, and will be used for large eddy simulation (LES) . Based on experimental and numerical results, the formation mechanism, flow characteristics, the development and propagation, as well as the influence of rotating stalls in the impeller and diffuser on the pump performance will be examined in detail for centrifugal pumps equipped with a vaned diffuser. In addition, the relationship among the rotating stall, geometric parameters and operation conditions will be studied. The internal complex flow structure before and after the occurrence of rotating stall will be analyzed.Furthermore, the methods to delay rotating stalls in centrifugal pumps will be discussed. This work can provide useful theoretical guidance for improving hydraulic performance and operational stability of centrifugal pumps.

旋转失速是离心泵内部常见的一种不稳定流动现象，通常发生在小流量工况下，会引起水泵运行时的性能不稳定，严重时会引起整个泵系统的共振。本项研究采用高精度三维粒子图像测速仪（TR-PIV）和微型高频压力传感器作为实验测量手段，对离心泵叶轮和导叶内旋转失速发生前后的内部流场进行精确测量。同时针对现有大涡模拟亚格子模型精度不足与模拟效率不高的缺陷，开发简单高效的亚格子模型，并采用大涡模拟对旋转失速进行数值仿真。基于实验测试和数值模拟结果，系统研究导叶式离心泵叶轮和导叶内旋转失速的产生机理、流动特征、发展和传播规律，以及对离心泵性能的影响；揭示离心泵内旋转失速与几何参数和运行参数之间的关系；深入分析旋转失速发生前后离心泵内部复杂流场结构；并建立能够有效延缓或抑制离心泵内部旋转失速产生的水力优化设计原则。本研究可为离心泵的水力性能及运行稳定性的提高提供有效的理论依据。

为了避免导叶式离心泵在小流量工况下运行时发生旋转失速现象，进而影响离心泵的运行性能、可靠性和安全性，本项目通过数值模拟和实验测试等方法，系统研究了导叶式离心泵叶轮和导叶流道内旋转失速的产生机理、流动特征、发展和传播规律，以及对离心泵性能的影响。利用TR-PIV得到了离心泵发生旋转失速前后叶轮流道内和导叶流道内的复杂流场结构，对所选湍流模型（大涡模拟和SST k-ω湍流模型）在预测离心泵旋转失速特性的精度进行了验证和对比。计算了离心泵叶轮内的失速特性（旋转失速和固定失速），并研究了不同叶片数、流量、非均匀来流（周向和径向非均匀来流）和加装导叶对叶轮内失速的影响；研究表明：叶轮叶片数为偶数时失速类型为固定失速，为奇数时则为旋转失速，且失速团的数目取决于离心泵的流量。此外，计算了离心泵导叶流道内的旋转失速特性，采用互功率谱分析方法确定失速类型及旋转失速，同时研究了导叶数目和径向间隙对导叶流道内旋转失速特性的影响。研究表明：当失速团数目和导叶叶片数不是整数倍的关系时，导叶叶片数只影响失速团的旋转频率，不改变失速团的失速形式；当叶轮外径的增大即叶轮与导叶间径向间隙的减小时，导叶流道内压力脉动和失速现象减弱，而叶轮流道内失速现象加剧。最后，研究了进口管壁面刻槽对失速的抑制和消除机理，并建立了能够有效延缓或抑制离心泵内部旋转失速产生的水力优化设计原则，包括改变叶轮叶片数、改变导叶叶片数、改变叶轮和导叶的径向间隙和进口管壁面刻槽。本研究有助于提高对导叶式离心泵旋转失速的认识，并为离心泵的水力设计和稳定运行提供了理论指导。