水泵水轮机开机过程水力特性研究

Study on hydraulic performance of pump-turbine in startup process

抽水蓄能电站水泵水轮机组在开机过程中产生剧烈的压力波动,转轮内复杂流动和压力脉动是引起固定部件强烈振动的主要原因之一。因此,需要对水泵水轮机开机过程的物理机理进行深入研究。本文同时建立了厦门抽水蓄能电站管路系统的一维特征线水力模型及水泵水轮机组过水流道的三维流场计算模型,开展了机组发电开机过程一维三维耦合的数值计算,重点分析了机组开机过程瞬时流动特点,以及转轮径向力和轴向力变化与外特性的内在关联性。研究发现,机组开机至空载状态时,由于导叶开度小、转速上升快,在无叶区形成了速率很高的水环,同时转轮流道内充斥着大量复杂的漩涡结构,导致了流量与转矩的突降。导叶动作、转速对径向力、轴向力的变化规律有直接的影响,开机过程中转轮径向力的变化趋势与活动导叶动作过程基本一致。轴向力的变化趋势与机组转速变化基本一致,转速和轴向水推力数值总体上为逐渐增大的趋势。本文研究结论为抽水蓄能机组和高水头混流式水轮机的开机过程物理机理和规律提供了有价值的参考。

During startup, severe pressure fluctuations usually occur in a pump-turbine;complex flows and pressure pulsations in its runner are two main causes for the strong vibration of its stationary parts.In-depth research is necessary on the physical mechanism of startup. This paper presents numerical simulations of a large pumped-storage power station, coupling a one-dimensional characteristic method hydraulic model of its pipeline system and a three-dimensional calculation model of the whole water passage of its pump-turbine unit. We focus on the analysis of the instantaneous flow characteristics of the unit and the internal correlation between its runner’s radial force and axial hydraulic thrust and its external characteristics during startup. The results show that when the unit is in no-load state, due to its small guide vane opening and a rapid increase in its rotational speed, a high-speed water ring is formed in its vaneless area, resulting in a sudden drop in its flow discharge and runner torque. The corresponding variations in the radial force and axial hydraulic thrust are complex and directly impacted by the variations in the guide vane opening and rotational speed. The trend of radial force roughly follows that of guide vane moving,while the trend of axial hydraulic thrust is nearly the same as that of the unit speed, both gradually increasing on the whole during startup. This study provides an in-depth understanding of the physical mechanism of the startup process and its variations of pumped-storage units and high-head Francis turbines.