混流式水轮机转轮应力分析及改善措施研究

发布时间：2018-03-21 16:21

本文选题：混流式水力机组　切入点：三角块　出处：《西安理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着混流式水力机组的容量、尺寸等的不断提高,不锈钢叶片相对减薄,转轮相对刚度则有所下降,再加上机组运行工况复杂,导致转轮叶片出水边近上冠处产生集中的高应力,这是造成转轮产生裂纹甚至断裂的重要因素,严重影响了机组的安全稳定运行。为了改善转轮的应力分布以达到减少叶片裂纹的目的。本文针对某一电站转轮叶片靠近出水边及上冠部分经常产生裂纹的情况,采用在转轮叶片出水边及上冠处加装三角块的方法,分析了不同尺寸三角块对转轮应力以及流场特性的影响。主要研究内容包括以下几个部分:首先,保证三角块L1 (三角块与叶片出水边相接边)边和L2 (三角块与上冠相接边)边尺寸在满足条件L1=L2下,通过对额定水头额定出力和最大水头额定出力工况下水轮机整个流道进行定常数值模拟,研究表明转轮应力随三角块尺寸的增大而持续减小,且最大应力转移到了叶片出水边与三角块出水边相接的转角处。其次,将计算得到的最优三角块尺寸作为进一步改善应力的基础尺寸,计算在三角块L2不变,增加L1情况下,两个工况下转轮的应力结果。研究表明转轮最大应力会随着L1边的增大而进一步降低。综合比较加装不同尺寸三角块对水轮机不同性能参数影响后,确定了最优的三角块尺寸约为L1/L2=2/1,L2约为转轮直径D1的5.7%,为转轮叶片出水边的10%,为叶片正面与上冠面交线的18%。其对水轮机的出力,效率,转轮变形等影响较小;转轮最大应力值只有原先的40%左右。然后,根据某电站出现的在部分负荷工况下机组振动问题,计算了加装最优尺寸三角块转轮的应力情况。得出三角块在部分负荷仍然能有效地降低转轮最大应力,表明三角块在水轮机不同的工况下都能改善转轮应力分布。最后,分别对不同工况下不同转轮进行全流道非定常计算,分析机组内部的三维非定常流动特性。研究发现整体上转轮和尾水管流域内压力脉动频率基本不受三角块影响,压力脉动幅值变化在3%以内。
[Abstract]:With the continuous improvement of the capacity and size of the Francis hydraulic unit, the stainless steel blade is relatively thin, the relative stiffness of the runner is decreased, and the operating conditions of the unit are complicated. The high stress concentration on the edge of the runner blade near the upper crown is an important factor causing cracks and even fracture of the runner. In order to improve the stress distribution of runner so as to reduce the crack of blade, this paper deals with the situation that cracks often occur in the blade near the outlet edge and the upper crown of the runner blade in a certain power station. The influence of different sizes of triangular blocks on the stress and flow field characteristics of runner blades is analyzed by adding triangle blocks to the outlet edge and upper crown of runner blades. The main research contents are as follows: first of all, Ensure that the dimensions of triangle block L1 (triangle block and blade outlet edge) edge and L 2 (triangle block and upper crown edge) edge are satisfied under the condition L1 / L 2, Through the steady numerical simulation of the whole runner of the turbine under the condition of rated water head rated force and maximum head rated force, the research shows that the runner stress decreases continuously with the increase of triangle block size. And the maximum stress is transferred to the corner where the blade outlet edge is connected with the triangular block outlet edge. Secondly, the calculated optimum triangle block size is taken as the basic dimension to further improve the stress, and the calculation is made under the condition that the triangle block L2 is invariant and the L1 is increased. The results of stress of the runner under two working conditions show that the maximum stress of the runner decreases further with the increase of the L1 side. The optimum size of triangle block is about L 1 / L 2 / 2 / L 2 is about 5.7 of runner diameter D1, 10 of runner blade water edge and 18 of the intersection line of blade front and upper crown. Its influence on turbine force, efficiency, wheel deformation and so on is relatively small, the results show that the optimum triangle block size is about L 1 / L 2 / 2 / L 2, about 5.7 of runner diameter D1, 10 of runner blade and 10 of water edge, and 18 of the intersection line between the front of the blade and the upper crown. The maximum stress of the runner is only about 40% of the original value. Then, according to the vibration problem of the unit under partial load conditions, The stress of the rotary wheel with the optimal size is calculated. It is concluded that the triangle block can effectively reduce the maximum stress of the runner under partial load, which indicates that the triangle block can improve the stress distribution of the runner under different working conditions of the turbine. The unsteady flow characteristics of three dimensional unsteady flow in the whole runner and draft tube basin are analyzed. The results show that the pressure pulsation frequency in the whole runner and draft tube basin is almost unaffected by the triangle block. The amplitude of pressure fluctuation varies within 3%.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV734

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