水泵水轮机低水头起动过程压力脉动与内流演变研究

Study on pressure pulsation and internal flow evolution of pump turbine during low-head start-up process

摘要

【目的】抽蓄机组在低水头起动时容易进入其全特性曲线的反S不稳定区，从而导致机组并网失败，严重影响机组的安全稳定运行。【方法】通过三维数值模拟方法对某抽水蓄能电站水泵水轮机全过流系统的低水头起动过程进行研究，重点分析蜗壳与导叶转轮区域的压力脉动以及内部流动特性。【结果】模拟结果显示：在抽蓄机组低水头起动过程中，导叶开启阶段，转轮进口、转轮叶片内部存在旋涡阻塞流道使流量降低，产生水锤效应使转轮上游压力迅速增大，旋涡结构随水锤高压减少后，流量迅速增加，又导致小幅度的负水锤使压力降低。导叶停止运动后，转轮进口和出口的涡结构分布减少，随着转轮力矩继续降低，机组进入反S区并接近空载工况，压力脉动开始增强，转轮叶片前缘和尾缘重新产生不稳定涡结构，转轮出口水流流速的增加导致尾水管涡带向下游延伸并变为中心和近壁面的双层涡结构。【结论】一些漩涡结构是导致机组在起动初期外特性参数不稳定的主要原因。随着起动过程的进行，压力脉动开始增强，转轮流道内重新产生不稳定涡结构，造成了水泵水轮机空载不稳定的水力特性。通过对蜗壳与导叶转轮区域的压力脉动以及内部流动特性的分析，以期为抽蓄机组低水头稳定起动提供参考。

Abstract

[Objective] During the low-head start-up of pumped-storage units, units are prone to entering the unstable reverse-S zone of the full characteristic curve, which can lead to failure in grid connection and severely affect the safe and stable operation of the units. [Methods] A three-dimensional numerical simulation was conducted to study the low-head start-up process of the full-flow system in a pumped-storage hydropower plant's pump-turbine units, focusing on analyzing pressure pulsations in the volute and guide vane impeller regions, as well as internal flow characteristics. [Results] The simulation result showed that during the low-head start-up process of the pumped-storage units, in the stage of guide vane opening, vortices and blocked flow paths at the impeller inlet and within the impeller blades reduced the flow, generating a water hammer effect that rapidly increased the upstream pressure of the impeller. As the high pressure caused by the water hammer dissipated, the flow increased rapidly, followed by a slight negative water hammer that caused the pressure to drop. After the guide vanes stopped moving, the distribution of vortex structures at the impeller inlet and outlet decreased. As the impeller torque continued to decrease, the units entered the reverse-S zone and approached the no-load operating condition, with pressure pulsations starting to intensify. Unstable vortex structures reappeared at the leading and trailing edges of the impeller blades, and the increased water flow velocity at the impeller outlet caused the vortex belt in the tailwater pipe to extend downstream, forming a double-layer vortex structure at the center and near the wall. [Conclusion] Some vortex structures are the main cause of the instability of the units' external characteristic parameters at the beginning of the start-up process. As the process continues, pressure pulsations begin to increase, and unstable vortex structures reappear within the impeller flow passages, [Results] ing in the unstable hydraulic characteristics of the pump turbine under no-load conditions. The analysis of pressure pulsations and internal flow characteristics in the volute and guide vane impeller regions aims to provide a reference for achieving stable low-head start-up of the pumped-storage units.

关键词

抽水蓄能电站 / 水泵水轮机 / 反S特性 / 低水头起动 / 压力脉动 / 流动特性

Key words

pumped-storage power station / pump turbine / reverse-S characteristic / low-head start-up / pressure pulsation / flow characteristics

基金资助

国家自然科学基金项目(52379086)