水泵水轮机泵工况FLI驼峰与迟滞效应流动机理的研究

Full load instability in the performance curve of pump turbine on pump mode, including hump and hysteresis, is one of the key issues which affect the safe and stable operation of pumped storage station. So far, there is no consensus theory to explain the causes of this instability and hysteresis. In this project, dynamic pressure measurement, high-speed flow visualization and numerical simulation are adopted to study the unsteady flow in this instability region. Firstly, analyses of the results of high-speed flow visualization and simulation, which are obtained at initial state of the hysteresis, are conducted to explore the relationship between the unsteady flows and the trigger condition of hysteresis. Secondly, an analysis system is established to diagnose the dynamic characteristics of the unsteady flow inner pump turbine on pump mode. The dynamic pressure signals from diffuser are analyzed by this system to get the characteristics of the main unsteady flows in this instability region. Thirdly, based on the characteristic frequencies of the unsteady flows, frequency analysis of the flow field visualization both by high-speed flow visualization and simulation are carried out to obtain the distribution of these unsteady flows. On the basis of the above analysis, some meaningful results, which can be provided to contribute the understanding on origins and development of the unsteady flow inner pump turbine in this instability region, could guide the design and optimization of the pump turbine.

水泵水轮机泵工况下性能曲线在近设计点出现的驼峰及伴随的迟滞效应(又称为FLI)是制约抽水蓄能电站安全稳定运行的瓶颈之一。目前，学术界对该驼峰及其迟滞效应的成因与机理尚未形成统一解释。本项目将基于实验和数值模拟，采用流场可视化特征量频域分析法，研究引起该现象的流动机理，进而提出控制策略。首先，通过高速摄影与数值模拟，获取迟滞效应初始时叶轮出口及导叶流道内流场的流态分布，探索各种流动现象如流动分离、回流、失速等与迟滞效应触发之间的关系。其次，建立水泵水轮机泵工况内部非定常流动诊断系统，通过分析导叶内动态压力信息获得发生该现象时导叶流道内的主要非定常流动的特征，包括特征频率、传播特征等。根据获得的非定流动特征频率，结合可视化流场特征量频域分析方法，获得非定常流动分布情况及发展规律对特性曲线FLI驼峰与其迟滞效应的影响，提出改善及抑制方法。

随着我国核能、风能及太阳能发电的增长，抽水蓄能作为理想的电网大规模调峰设备和能量存储方式，对其调控能力提出了更高的要求。水泵水轮机作为抽水蓄能的核心部件，其近FLI驼峰现象不仅严重制约着其稳定运行范围，也是影响抽水蓄能电站安全与经济运行的关键问题。.本项目基于流场特征量一维频域分析的优势和流场可视化方法的特点，建立一种水泵水轮机泵工况内部非定常流动诊断及二维成像方法。并采用该方法对水泵水轮机泵工况下的FLI驼峰不稳定性流动机理进行试验及数值仿真研究，研究表明：该不稳定现象主要是可调导叶流道内两种不稳定流动相互作用导致的。一种是受叶轮内部特征频率为St≈0.3325的非定常流动影响从而在可调导叶进口附近形成相应特征频率的非受迫非定常流动结构。另一种非定常流动结构是受U型扭曲固定导叶内特征频率为St≈0.6625的非定常流动影响，在可调导叶出口处形成的相应非定常流动结构，该结构随着流量逐渐减小沿着可调导叶向进口处移动。在临界流量点0.6倍设计流量附近，以上两种流动在导叶进口附近相互作用造成较大能量损失，从而导致扬程减小即FLI驼峰形成。同时在试验及数值模拟结果的对比中发现，数值仿真过程中水的可压缩性对非定常流动引起的压力脉动幅值影响显著。基于该问题本项目提出的适用于离心泵的弱可压缩计算模型，对比分析表明忽略水的可压缩性是导致非受迫不稳定流动结构在其特征频率下试验压力脉动幅值明显大于仿真结果的原因之一。以上研究成果对我国中高比转速水泵水轮机稳定性运行设计具有一定的工程和学术价值。.在本项目支持下，研究成果多发表在本领域一流期刊，包含1篇ASME of Turbomachinery 、1篇Renewable Energy、1篇Journal of Thermal Science及两篇EI检索论文并申请发明专利一项。同时所提出的非定常流动诊断方法也在项目“叶片泵流动诱导特性与水力优化技术及应用”应用获得国家科学技术进步二等奖。