畸变进流条件下轴流泵失稳特性及内流机理研究

Constrained by the on-spot project conditions, the inlet passage, more often than not, cannot provide even inlet flow fields for the axial-flow pump inlet, when the pump unit in large -scale pump station is in actual motion. This phenomenon has exerted a great impact on the pump capability and its running stability. The testing technologies, such as 3D-LDV and 3D-PIV and the CFD calculating technology develop very quickly and have been widely applied in testing and analyzing pump flow fields, but their use is mainly limited to the research on axial-flow pump impeller flow mechanism. This project aims to test and analyze the non-stationary characteristics of the axial-flow pump impeller with high specific speed under the condition of uneven inlet flow fields, makes full use of the testing technologies, such as 3D-LDV and 3D-PIV to test the time-averaged space flow fields and discontinuously-followed real-time flow fields inside and outside the axial-flow pump impeller, improves the impeller's non-stationary calculation models and methods, and predicts hydraulic performance and hydraulic pressure fluctuations. With the analysis of the small waves randomly, this project also aims to reveal how the inlet flow fields affect the flow and performance of the inside of the impeller, get familiarized with the impeller's responses to the uneven inlet flow fields, and quantify the index of the uneven inlet flow structure and pump performance stability. The research results are able to provide more accurate objective functions for the optimal design of the inlet passage and important reference for improving the optimal design of the impeller's stability index, and are able to improve the pump station's reliability in actual motion effectively.

大型轴流泵装置在实际运行时，因受到工程现场条件的限制，进水流道往往不能为泵进口提供均匀的进水流场，对轴流泵性能极其运行稳定性产生极大影响。3D-LDV、3D-PIV 测试技术和CFD计算技术发展迅速，在泵内流场测试分析中已普遍应用，但主要集中于轴流泵叶轮自身流动机理的研究。本项目测试分析在畸变入流条件下的轴流泵叶轮失稳特性，利用3D-LDV、3D-PIV测量叶轮内外时均空间流场和间断跟踪实时流场，改进轴流泵的非定常计算模型和计算方法，预测水力性能和水压脉动。通过小波随机分析等技术手段揭示进口流场对泵叶轮内部流动和性能的影响机理，掌握轴流泵叶轮对畸变入流条件下的响应特性，建立失稳模型，量化畸变入流进口流场结构与轴流泵性能稳定性等指标。研究成果可为进水流道优化设计提供更加明确的目标函数，为提高轴流泵稳定性指标的优化设计和泵站运行安全可靠性提供重要的理论支撑。

大型轴流泵装置在实际运行时，因受到工程现场条件的限制，进水流道往往不能为泵进口提供均匀的进水流场，对轴流泵性能及其运行稳定性产生极大影响。本项目通过模型试验和数值模拟相结合的研究手段对轴流泵失速工况下表现出来的内流场非定常特性进行深入的分析。项目主要研究内容可分为轴流泵小流量工况下的外特性水力性能性能试验、高速摄像机拍摄叶轮进口及内部的流场结构、叶轮室进出口压力脉动测试与分析、叶轮内部三维速度场的LDV测试和轴流泵内流场的数值模拟研究五个方面。本项目研究得到的主要创新性成果有，轴流泵流量扬程曲线在通常认为的马鞍区之前存在另一个拐点，类似一段小马鞍区，该区域轴流泵内流场运行基本稳定，主要是由于叶轮进口外缘的切向速度受叶轮旋转的诱导增长较快，引起水流的冲角减小所致。当轴流泵处于不稳定运行区域时，叶片背面尾缘近轮缘侧出现不稳定的通道涡结构，对应叶轮进口出现了不稳定的来流速度分布，导致叶轮运行不稳定。在失速前，叶轮近轮毂和轮缘侧已开始出现回流结构，失速后，叶轮通道内形成的通道涡带结构相对叶片保持稳定，涡带与叶轮旋转方向相同，一直延伸至叶轮的进口，在此涡带的影响下，叶轮进口的压力脉动向来流方向延伸，叶轮出口的压力脉动峰值开始大于叶轮进口。流量扬程的不稳定为通道涡的不稳定性造成，而失速后，扬程降低是通道涡引起的水力损失过大所致。阐述了压力脉动分布与叶轮进口切向速度变化的关系。在流量扬程曲线出现拐点的地方，受间隙泄漏涡的影响叶轮进口频谱图出现宽带低频分布。间隙泄漏涡在扩散的同时，频率不断发生变化，引起了进口压力脉动出现了宽带低频的分布现象，且随着流量减小，叶片正负压力差值增大，泄漏涡增强，影响范围扩大，频率减小，分布范围向低频带迁移。探讨了轴流泵失速形成的规律，揭示了轴流泵叶轮内部不稳定流动的三维非定常现象，在扩宽轴流泵的稳定运行范围和提高轴流泵在极端条件下的应急能力等方面具有重要的社会价值。