灯泡贯流式水轮机在小流量工况下的内流特性分析

ANALYSIS OF INTERNAL FLOW CHARACTERISTICS OF BULB TUBULAR TURBINE UNDER LOW FLOW CONDITION

为了研究灯泡贯流式水轮机在小流量工况下的内流特性,以某水电站贯流式水轮机为研究对象,利用RNG k-ε湍流模型对全流道进行数值计算,分析在小流量工况下尾水管恢复系数和全流道流动情况,并定量分析水轮机部分过流部件的压力脉动情况。结果表明:在小流量工况下当电站水头和导叶开度不匹配时,尾水管的恢复系数减小,当尾水管恢复系数减小2%~3%时,机组效率降低1%;受转轮主流区和尾水管死水区的相互作用,在尾水管边壁会形成漩涡结构,有明显的回流且在边壁存在高速流体;在小流量工况下,机组主要受低频压力脉动影响,转轮进口处的主频是由在转轮转动和导叶提供机组环量时产生的,在尾水管中主要受频率为0.2 Hz的低频压力脉动影响,压力脉动系数沿尾水管出口方向依次增大,最大为1.75%。

In order to study the internal flow characteristics of bulb tubular turbine under low flow condition,taking the tubular turbine of a hydropower station as the research object,the RNG k-ε turbulence model is used for numerical calculation,the draft tube efficiency of draft tube and the flow in the whole channel under the condition of low flow are analyzed,and the pressure pulsation of hydraulic turbine flow parts is analyzed quantitatively.The analysis shows that when the head and guide vane opening not match under the condition of low flow,the draft tube efficiency is reduced,the change trend of draft tube efficiency is related to unit efficiency,when the draft tube efficiency decreases by 2%-3%,the unit efficiency will decrease by 1%.Interaction between the main flow area of the runner and the water flow Static area of the draft tube,vortex structure is formed on the side wall of draft tube,there is obvious backflow in the draft tube and high-speed fluid exists in the side wall.Pressure fluctuation is more prominent under low flow conditions,mainly affected by low frequency pressure fluctuation,the main frequency at the inlet of the runner comes from the circulation of the unit provided by the guide vane,which is close to the blade frequency of the runner.In the draft tube,it is mainly affected by low frequency pressure fluctuation with 0.2 Hz,the pressure fluctuation coefficient increases along the draft tube,the maximum pressure fluctuation coefficient is 1.75%.