混流式水轮机主轴中心孔补水对尾水管性能的影响

发布时间：2019-03-22 14:42

【摘要】：混流式水轮机在低负荷工况下运行时,尾水管内出现旋转的偏心涡带,会引起强烈的压力脉动和振动,严重威胁厂房的安全。为了使机组稳定运行,该文提出了一种通过从上冠泄水锥引入高压补水的方法来降低尾水管的不稳定性。该文首先采用商业软件CFX16.0,对某电站混流式水轮机在低负荷工况下进行了可靠而准确的全三维非定常数值模拟,结果表明在该工况下尾水管内部存在明显的偏心涡带,并伴随着振幅较大的压力脉动,这与试验结果相吻合。其次,对该工况下不同补水流量进行了数值模拟计算,研究表明:尾水管内补高压水可以有效降低尾水管内部的流动损失,且随着补水量的增加而越小,但过大的补水量会引起叶片正背面压力的降低,影响水轮机的空化性能,故补水量的大小必须综合考虑;主轴中心孔高压补水可以增加转轮出口的轴向速度,从而改变涡带内速度场的分布,可有效消除回流现象,当补水流量过小时,抑制回流作用不明显;当补水量为进口流量1%时,尾水管内部压力脉动振幅变化不大,改善效果不明显;当补水量为进口流量3%时,尾水管内部涡带由双螺旋变成单螺旋,锥管段压力脉动振幅不减反增,不稳定性有所加剧;当补水量为进口流量5%时,尾水管内部压力脉动振幅从18.4%降低至1.63%,同时改变了压力脉动的主频,使其远离转轮主频,避免发生共振,提高了机组的稳定性。
[Abstract]:When Francis turbine is operated under low load condition, rotating eccentric vortex belt appears in draft pipe, which will cause strong pressure pulsation and vibration, and seriously threaten the safety of factory building. In order to make the unit run stably, this paper presents a method to reduce the instability of draft pipe by introducing high pressure replenishment water from the top crown discharge cone. In this paper, a reliable and accurate three-dimensional unsteady numerical simulation of a Francis turbine in a power station under low load condition is carried out by using commercial software CFX16.0,. The results show that there is an obvious eccentric vortex band in the draft pipe under this condition. The pressure fluctuation with larger amplitude is in good agreement with the experimental results. Secondly, the numerical simulation of different recharge flow rates under this condition is carried out. The results show that high pressure water replenishment in draft tube can effectively reduce the flow loss in draft pipe, and the smaller the flow loss is with the increase of water supply, the smaller the flow loss in the draft pipe is. However, excessive recharge will reduce the pressure on the positive back of the blade and affect the cavitation performance of the turbine. Therefore, the amount of water replenishment must be considered comprehensively. High pressure recharge of the central hole of the spindle can increase the axial velocity at the outlet of the runner, thus changing the distribution of the velocity field in the vortex belt and effectively eliminating the reflux phenomenon. When the recharge flow rate is too small, the refluxing inhibition effect is not obvious. When the inlet flow rate is 1%, the amplitude of pressure fluctuation in the draft pipe does not change much, and the improvement effect is not obvious. When the inlet flow rate is 3%, the vortex band in the draft pipe changes from double helix to single helix, and the amplitude of pressure fluctuation in the cone section increases, and the instability increases. When the inlet flow rate is 5%, the pressure fluctuation amplitude in the draft pipe decreases from 18.4% to 1.63%. At the same time, the main frequency of the pressure fluctuation is changed so that it is far away from the main frequency of the runner, so as to avoid resonance and improve the stability of the unit.
【作者单位】：西安理工大学水利水电学院;
【基金】：国家自然科学基金(51679195,51339005,51379174)
【分类号】：TK733.1

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