【作者】 宋兵伟；

【导师】 马震岳； 辻本良信；

【作者基本信息】 大连理工大学 ， 水利水电工程， 2010， 博士

【摘要】 随着经济与社会的发展,水电事业也在最近的几十年间取得了飞速的发展,随着混流式水轮机组单机容量和引用水头的增大,其结构也更加复杂,随之而来的机组稳定性问题也日益突出。长期以来水轮发电机组的横向振动问题受到国内外研究者的普遍重视,特别是混流式水轮机组,当负荷超过一定值时会发生强烈的弯曲振动,振动一旦发生,振幅就会不断增大进而导致整个机组甚至厂房的振动。经检验分析,导致此类弯曲振动的原因之一是通过水轮机上冠间隙内的不平衡流体所产生的流体力和力矩,因此本文针对此类工程实际问题,设计了混流式水轮机涡动和进动过程中测量上冠间隙内部流场和流体力的试验；建立了转轮涡动和进动过程中计算密封内部流场和作用在转轮上冠流体力的数值模型；分析了涡动流体力矩和进动流体力矩的自激效应；探讨了流体动力矩对轴系稳定性的影响。研究结果可为分析混流式水轮机组的稳定性提供理论依据和参考。第一章为绪论部分。结合国内外对于混流式水轮机组流体激振的研究现状和工程实际提出课题的研究背景和意义。介绍了关于密封流体激振的国内外研究现状与进展,并对密封流体激振在转子涡动和进动两方面的研究进展进行归纳和总结。第二章为模型试验部分。介绍了模型试验所用的试验装置、试验参数的选取和所使用的试验方法。进行了四轴力传感器的校核试验,得到了用于传递示波器输出与作用在轴端的外力之间的传递矩阵。进行了混流式水轮机转轮涡动、进动过程的惯性力计算和试验,分析了计算结果和试验结果的有效性。同时,概括性地介绍了流体力试验的方法和内容。第三章为数值模拟部分。采用简化的N-S方程,结合转轮上冠密封的几何形状,建立了计算混流式水轮机涡动和进动过程中间隙内部流场分布特性和作用在上冠的流体力和流体力矩的整体流动数值模型,探讨了整体流动模型的数值解法。利用计算机Fortran语言编写了整体流动数值模型的计算程序。第四章为混流式水轮机涡动过程中作用在转轮上冠的流体力矩的自激效应研究。进行了混流式水轮机上冠间隙流的定常压力试验和数值模拟,研究了间隙流内部稳态流场的分布特性。建立了涡动流体力矩作用下悬臂梁转子轴系统的振动模型,得出用于判断涡动流体力矩是否具有自激效应的判断准则。通过试验和数值结果的对比,研究了泄漏流速、进口处预旋速度和轴向间隙宽度对涡动流体力矩随涡动速度比的变化曲线和自激效应的影响。分析了转轮涡动过程中,上冠间隙内部非稳态流场的分布特性。第五章为混流式水轮机进动过程中,作用在转轮上冠的流体力矩的自激效应研究。研究了混流式水轮机进动过程中,上冠间隙流内部的稳态流场分布特性。通过数值模拟和模型试验结果的对比,检验分析了间隙内泄漏流速、进口处预旋速度、轴向间隙宽度和转轮旋转对进动流体力矩自激效应的影响,探讨了进动过程中,间隙内部的非稳态流场分布特性。第六章为流体力矩所诱发的轴系不稳定性研究。通过对试验所得到的涡动和进动流体力矩进行曲线拟合,得到并讨论了由上冠密封所产生的转子动力特性系数。建立一集总参数数学模型,利用Matlab语言编制了模型的计算程序,对悬臂梁转子轴系统的稳定性进行了系统地研究和分析。更多还原

【Abstract】 With the developments of economy and society, the hydropower has developed rapidly in recent years. Hence with the increase in the capacity and the dimension of the hydroelectric generating set, the structure becomes more and more complicated. As a result, the problem of stability of a generating set is more and more prominent.Much attention has been paid on the lateral vibration of the hydroelectric generating set, especially the Francis turbine, for a long time. When the load exceeds a certain value, a severe flexural vibration will occur, and the amplitude will increase constantly. Furthermore, it can result in the vibration even destroy of the power house. After detailed checking, it was shown that this vibration is a kind of self-excited vibration which caused by the fluid force and moment acting on the backshroud of the runner associated with the leakage flow through the back chamber. As a result, based on the actual vibration problem, model tests were designed on the fundamental characteristics of the flow field in the crown clearance of a Francis turbine runner in whirling and precession motions, respectively. And so the fluid forces and moments under various conditions were measured. The numerical simulation model was established to calculate the characteristics of the flow field in the clearance and the fluid forces and moments. The self-excited effect of the whirling moment and precession moment was analyzed. The stability of a cantilevered shaft-disk system subjected to each fluid moment was discussed. These conclusions can provide the material and the reference of this kind of self-excited vibration of the Francis turbine.Chapter one is the introduction section. According to the research status of the topic on the vibration induced by the fluid of the Francis turbine at home and abroad, the background and the significance of this research topic are put forward. The home and abroad research status and progress of vibration excited by the seal or clearance flow are introduced. The advance of the vibration induced by the clearance flow in the aspects of whirling and precession motions are concluded and summarized, respectively.The second chapter is about the model test. The experimental apparatus, the selection of the parameters and the methodology of the measurement of the experiment were introduced. The calibration test of the four-axis force sensor dynamometer was conducted to get the transfer matrix between the force acting on the end of the cantilevered shaft and the output of the digital scope. The inertia test was also conducted theoretically and experimentally, and the results of the calculation and experiment were compared and validated. The method and the content of the fluid force measurement were generally introduced.The third chapter is about the numerical simulation. Based on the simplified Navier-Stokes equations and the geometry of the crown clearance of the Francis turbine runner, the numerical bulk flow model was established to calculate the steady and unsteady flow field characteristics in the crown clearance and the fluid forces and moments on the crown of the runner in whirling and precession motions. The solutions of the steady and unsteady components were discussed. The computational program of the bulk flow model based on the computer language Fortran was made for calculation.The fourth chapter is about the self-excited effect of the whirling moment acting on the crown of the Francis turbine runner. The steady pressure experiments and calculations under various conditions in the crown clearance of the Francis turbine runner were carried out in order to study about the fundamental characteristics of the steady flow field distribution. The stability analysis model of a cantilevered shaft disk system subjected to the whirl moment was established through the structural coupling between the linear and angular displacement. The criterion for determining the self-excited effect of the whirl moment was obtained. Through the comparison of the experimental result and the computational result of the whirl moment under various leakage flow rates, various preswirl velocities at the inlet of the radial clearance and various widths of the axial clearance, the self-excited effect of the whirl moment and the unsteady flow filed distribution were discussed.The fifth chapter is about the self-excited effect of the precession moment acting on the crown of the Francis turbine runner. The characteristics of the steady flow field in the clearance in precession motion were studied by model test and numerical simulation. Through the comparison of the computational and the experimental results, the self-excited effects of the precession moments were analyzed. The effect of the leakage flow rate in the clearance, the preswirl velocity, the axial clearance and the rotation of the disk on the precession moment were examined, respectively. The unsteady flow field distributions in the clearance in precession motion were discussed under various conditions.The sixth chapter is about the instability analysis of the cantilevered shaft disk system under the fluid force moments. The rotordynamic coefficients used in the rotordynamic instability analysis were obtained by curve fitting the experimental results of the whirling and precession moments, respectively. The effect of the coefficients on the instability was discussed. Through establishing a lumped parameter model subjected to the whirl and/or the precession moment(s) by using Matlab software, the instabilities of the system were discussed and analyzed.更多还原