基于凹槽抽吸和Coanda射流的离心泵自循环端壁扩稳机理研究

Rotating Stall vortex in the impeller and inflow distortion under low flow rate condition are the key issues that lead to the instability of centrifugal pump. In this project, the high-precision TR-PIV and LDV will be applied to test the internal flow field of a semi-open centrifugal pump impeller. The flow characteristics of the rotating stall vortex and the effect on the operation stability of centrifugal pump will be analyzed. By means of the LES simulation, according to the existing SGS model is not accurate, a wall's self-adaptive mixed-time-scale SGS model that can accurately simulate the complex flow of the centrifugal pump in small flow rate condition will be developed. Based on the results of experimental tests and numerical simulations, the mechanism of the inhibition of the large-scale rotating stall vortex by the slotting on the endwall and sucking the fluid will be systematically studied. The relationship between the geometric characteristics of endwall slotting and the stall margin will be established. The mechanism of reducing the distortion by introducing a Coanda annular jet in the mainstream of the impeller inlet will be revealed. The principle of hydraulic optimal design of the endwall slotting self-circulating casing treatment technology and inlet Coanda nozzles will be studied. A self-circulation endwall treatment scheme that can delay or suppress large-scale rotating stall vortex and effectively reduce the inflow distortion will be proposed. The research results of this project will provide scientific basis for self-circulation endwall treatment to improve the operation stability of centrifugal pump.

小流量工况下叶轮内的旋转失速涡团和畸变入流是导致离心泵运行不稳定的关键核心问题。本项目拟采用TR-PIV和LDV对半开叶轮离心泵内部流动进行测试，分析叶轮内旋转失速涡团的产生、发展、脱落的流动特征及其对离心泵运行稳定性的影响规律；同时针对现有大涡模拟SGS模型预示精度不高的问题，开发可以精准模拟小流量离心泵内部复杂流动的壁面自适应混合时间尺度的SGS模型。基于实验测试和数值模拟的结果，系统研究离心泵叶顶端壁开槽和流体抽吸对大尺度旋转失速涡团的抑制机理，建立端壁开槽的几何特征和离心泵失速裕度之间的关联模型，揭示在叶轮入口前的主流中引入Coanda环状射流从而降低畸变度的机制，明确自循环端壁处理技术端壁开槽和入口Coanda喷嘴的水力优化设计原则，构建能够延缓或抑制大尺度旋转失速涡团并可以有效降低入流畸变度的自循环端壁处理方案。项目成果为自循环端壁处理用于离心泵的扩稳提供科学依据。

小流量工况下叶轮内的旋转失速涡团和畸变入流是导致离心泵运行不稳定的关键核心问题，项目针对该问题构建了离心泵整体水力性能与内部流动实验测试系统，发展了高精度数值模拟方法，采用数值模拟和实验相结合的方法，对不稳定流动诱发流动失稳的机理及抑制方法进行了研究。首先，研究了泄漏涡的结构特性和非定常特性，揭示了泄漏涡诱发失速从而引起振动的机理，泄漏涡破碎后形成前缘溢流和回流涡，会导致叶轮与进口管交界面附近出现低速区，叶片前缘角分离所造成的堵塞效应强于叶顶泄漏涡，角分离迅速在近轮毂处形成失速团并发展为全叶高失速，诱发低频压力脉动和振动，从而明晰了非稳定流动与振动的关系。其次，提出了周向槽、轴向槽等多种流动控制方法，阐明了端壁开槽的几何特征和离心泵整体水力性能、叶轮进口流动的影响规律，周向槽使泄漏涡的初始位置向下游移动，为前缘溢流提供周向通道，能够有效抑制甚至消除小流量工况下的回流现象；轴向槽将叶顶附近的分离涡移动至轴向槽内，形成两个成反向旋转的涡团，改善叶尖处叶顶附近的回流涡，上述流动控制方法能够抑制不稳定流动及其诱发的压力脉动，从而揭示了端壁处理对泄漏流及压力脉动的抑制机理，明确了对驼峰的影响规律，并明晰了端壁开槽的水力优化设计原则。此外，发展了自循环端壁处理技术与T型叶片技术，降低了过流部件的水力损失、提高叶轮的欧拉扬程，从而提升离心泵扬程和效率。本项目提出的端壁处理流动控制方法可以有效抑制离心泵叶轮通道内大尺度旋转失速涡团，降低入流畸变，提升水力性能，降低压力脉动和振动，为提高离心式水力机械的安全稳定性提供了理论和技术支撑。