水泵水轮机空化特性及过渡过程数值模拟研究

发布时间：2018-06-30 17:17

本文选题：水泵水轮机 + 过渡过程　；参考：《武汉大学》2017年硕士论文

【摘要】：抽水蓄能电站因其具有调峰调频及吸收多余电能的优势而被广泛建设与应用,但正是它的调节频繁使得水泵水轮机常处于剧烈的过渡过程当中。空化是影响水力机械安全运行的重要因素之一,空化腔不断的生成与溃灭常常导致转轮及导叶等部件严重空蚀,不得不停机进行检修,甚至引发剧烈的反水击现象,造成抬机等事故。因此对于水泵水轮机空化特性的研究具有十分重要的工程价值,并为抬机事故机理分析奠定基础。而对于水泵水轮机过渡过程压力脉动时频特性的研究则更能全面分析抽水蓄能电站各类不稳定现象的根源,并为这些不稳定现象的控制措施提供指导。本文分别采用三维CFD方法和一维三维耦合方法研究了水泵水轮机的空化特性和水泵断电飞逸过渡过程的压力脉动时频特性,并分析了压力脉动频率特性与流态特性相关联,揭示了过渡过程中多种频率的来源分布及影响;最后通过模拟球阀关闭联合水泵水轮机导叶拒动飞逸工况,分析了球阀关闭对其过渡过程外特性及压力脉动特性的影响,为优化球阀关闭规律以控制脉动不稳定性奠定了基础。本文主要工作如下:1.研究了原型水泵水轮机空化特性:为了规避空化特性研究中比尺效应的问题,模拟研究了某原型水泵水轮机在不同空化系数下空化特性。发现水泵水轮机的空化压力脉动幅值随空化系数的降低先增大后减小;揭示了发源于泄水锥下方的空化腔在形态、大小及历时上的随机性是空化压力脉动频域丰富但幅值较小的根本原因;解释了空化压力脉动在整个流道内的传播规律并分析了空化压力脉动的频域特性。2.全面分析了水泵断电飞逸过渡过程中压力脉动特性及流态特性:采用一维三维耦合方法模拟了某模型水泵水轮机水泵断电飞逸过渡过程,全面定量分析了各个位置压力脉动频率特性,研究了流态特性演变规律及其与压力脉动特性的关联。发现了高频低幅,高频高幅,中频中幅,低频高幅这四种典型的频率类型;揭示了各种频率的来源及空间影响范围,发现高频信号是由于转轮旋转引起的,主要影响无叶区,低频是由工况区转换导致的,影响整个流道,中频信号主要影响尾水管区域,其中中低频是由高能量的螺旋涡带引起的,中高频是由能量较小的螺旋涡带及尾水管边壁的片状涡带旋转产生的;分析了整个过渡过程中蜗壳压强,转轮内流线及尾水管涡带的演变规律,定性上解释了在水泵驼峰区及水轮机水轮机反S区流态恶化是导致宏观参数振动及中频频率丰富的根本原因。3.分析了飞逸过渡过程中球阀关闭的影响:采用一维三维耦合方法模拟了某模型水泵水轮机在飞逸过渡过程中两种球阀关闭工况,分析了球阀关闭对过渡过程中宏观参数及压力脉动的影响。发现飞逸过渡过程中球阀先快后慢关闭在解决调保矛盾及降低转轮受力方面要优于线性关闭;分析了无叶区内速度脉动及回流特性,发现无叶区纵向断面中部会形成回流,回流区域个数为转轮叶片数,回流在整个反S区均会存在,宏观流量的变化会影响正向流动和回流区域的分布。本文完成了水泵水轮机空化特性及过渡过程中振动特性的研究,全面定量地揭示了水泵水轮机在过渡过程中的频率特性。研究成果补充了现有对水泵水轮机空化特性及过渡过程中压力脉动时频特性及流态特性认识的不足,所得结论为将来研究水泵水轮机在极端过渡中空化腔溃灭反水击问题及减小机组振动措施奠定了基础。
[Abstract]:Pumped storage power station is widely constructed and applied because of its advantages of peak frequency modulation and absorption of excess electric energy, but it is its frequent adjustment that the pump turbine is often in a violent transition process. Cavitation is one of the important factors affecting the safe operation of hydraulic machinery. The continuous formation and collapse of the cavitation cavity often lead to the wheel. As well as the serious cavitation of the guide vane and other parts, it has to stop for overhaul and even cause severe backwater shock and cause accidents. Therefore, it is of great engineering value to study the cavitation characteristics of the pump turbine, and lay the foundation for the analysis of the mechanism of the lift. The study of characteristics can make a comprehensive analysis of the root causes of various instability phenomena in pumped storage power stations and provide guidance for the control measures of these unstable phenomena. In this paper, the three-dimensional CFD method and one dimensional three-dimensional coupling method are used to study the cavitation characteristics of the pump turbine and the time frequency characteristics of the pressure pulsation in the runaway process of the water pump. The relationship between the frequency characteristics of pressure pulsation and the flow characteristics is analyzed, and the source distribution and influence of various frequencies in the transition process are revealed. Finally, the effect of the shutoff on the characteristics of the transition process and the pressure pulsation characteristics of the pump valve is analyzed by simulating the shutoff of the valve and the effect of the pressure pulsation characteristics. The main work of this paper is to control the fluctuating instability. The main work of this paper is as follows: 1. the cavitation characteristics of the prototype pump turbine are studied. In order to avoid the problem of the scale effect in the study of the cavitation characteristics, the cavitation characteristics of a prototype pump turbine under the different cavitation coefficients are simulated and studied. The cavitation pressure fluctuation amplitude of the pump turbine is found. With the reduction of cavitation coefficient, it is revealed that the randomness of cavitation cavity originating under the discharge cone in shape, size and diachronic is the root cause of the rich but small amplitude in the frequency domain of cavitation pressure pulsation. The propagation rules of cavitation pressure pulsation in the whole flow channel are explained and the frequency domain characteristic of cavitation pressure pulsation.2 is analyzed. The characteristics of pressure pulsation and flow state in the process of water cut and runaway transition are analyzed. A one-dimensional three-dimensional coupling method is used to simulate the transition process of a model pump water pump, and the frequency characteristics of pressure pulsation in each position are analyzed. The evolution of flow characteristics and the characteristics of pressure pulsation are studied. The four typical frequency types, such as high frequency and low amplitude, high frequency and high amplitude, medium frequency medium amplitude and low frequency and high amplitude, are found. The sources of various frequencies and the range of spatial influence are revealed. It is found that the high frequency signal is caused by the rotation of the wheel, which mainly affects the non leaf area, the low frequency is caused by the conversion of the working condition area, and the main channel is influenced by the medium frequency signal. The middle low frequency is caused by the high energy spiral vortex belt, and the middle and high frequency is produced by the small spiral vortex belt and the flake vortex band of the side wall of the tail pipe. The variation law of the volute pressure, the inner flow line and the tail pipe vortex belt in the whole transition process is analyzed, and the water pump hump area and the water are explained qualitatively. The deterioration of the flow state in the reverse S zone of the turbine turbine is the root cause of the vibration of the macroscopic parameters and the rich frequency of the intermediate frequency. The effect of the shutoff of the ball valve in the process of flight transition is analyzed by.3.. The one dimension three-dimensional coupling method is used to simulate the closing of two kinds of ball valves in a model pump turbine during the runaway transition process, and the transition of the ball valve closing to the transition is analyzed. The effect of the macro parameters and pressure pulsation in the process is found. It is found that the ball valve is better than the linear closure in solving the contradiction of the adjustment and reducing the force of the runner, and the velocity fluctuation and reflux characteristics in the no leaf area are analyzed. The reflux exists in the whole anti S region. The change of the macroscopic flow will affect the distribution of the forward flow and the reflux region. This paper has completed the study on the cavitation characteristics of the pump turbine and the vibration characteristics during the transition process. The frequency characteristics of the pump turbine during the transition process are comprehensively and quantitatively revealed. The research results complement the existing water pump turbine. The characteristics of mechanical cavitation and the time frequency characteristics and flow characteristics of pressure pulsation in the process of transition are insufficient. The conclusion is the foundation for the future study of the pump turbine in the collapse of the reverse water shock in the extreme transition cavity and the measures to reduce the vibration of the unit.
【学位授予单位】：武汉大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV743;TV734

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