贯流式水轮机低频脉动及尾水管涡带特性研究

为了研究贯流式水轮机内部低频压力脉动特性,针对某电站贯流式水轮机进行了非定常数值计算,分析了不同工况下水轮机内部的压力脉动特性,揭示了贯流式水轮机低频压力脉动产生的机理,并提出了改善低频脉动的方案。研究表明,在额定工况和小流量工况下,水轮机内部的压力脉动主要受到叶片通过频率(5.26 Hz)以及低频脉动(0.20 Hz)的影响,低频脉动的幅值从水轮机进口到出口逐渐增加,且小流量工况的低频压力幅值较额定工况高;不同工况下,水轮机尾水管内均存在一个与转轮旋转方向一致的螺旋状偏心涡带,该涡带按一定周期演变,其对应频率为0.22 Hz,与低频压力脉动频率(0.20 Hz)较为接近,因此可以说明该水轮机内部的低频压力脉动是尾水管涡带引起的;为了减小水轮机低频压力脉动系数幅值,提出了一种在尾水管内增设导流板的方案,该方案能有效降低由尾水管涡带引起的低频压力脉动系数幅值,导流板通过降低尾水管内的涡带能量,达到消涡目的。研究结果可为贯流式水轮机组的稳定运行提供依据。

Investigation on Low Frequency Pulsating and Draft Tube Vortex of Tubular Turbine

In order to study the characteristics of low frequency pressure pulsation of tubular turbine, the unsteady internal flow field in a tubular turbine of a power station was numerically simulated. The pressure pulsation characteristics of the turbine under different working conditions were also analyzed. The UG software was used to build the model which mainly consisted of inlet conduit, bulb body, guide vane, runner and draft tube. The results showed that the pressure pulsation in the turbine was mainly affected by the rotation frequency of blade (5.26Hz) and the low-frequency pressure-pulse (0.20Hz) under the rated condition and low flow rate condition. The amplitude of the low frequency pulsation at 0.20Hz was increased gradually from the turbine inlet to the outlet. And the amplitude under the low flow rate condition was higher than that of the rated condition. There was a helical vortex rope in the draft tube which had the same direction with the runner hand of rotation. The frequency of the vortex rope in the draft tube was 0.22Hz. The low frequency pressure fluctuation frequency was mainly caused by the vortex rope. In order to reduce the influence of vortex rope, the deflector was used in the draft tube. The vortex was eliminated by reducing the energy of vortex. The steady operation of the turbine has been the focus in recent years. At the same time, the low-frequency pressure-pulse in the turbine was an important factor which affected the stable operation of the turbine. The research result had reference value for the stable operation of tubular turbine.