【作者】 王鹏；

【导师】 刘应征；

【作者基本信息】 上海交通大学 ， 动力工程及工程热物理， 2017， 博士

【摘要】 超超临界燃煤发电技术是目前世界上较为先进、成熟的洁净煤发电技术,具有非常高的运行可靠性、机组寿命以及热效率等。其中,超超临界汽轮机阀门是超超临界汽轮机控制系统中的重要元件,经常布置在汽轮机蒸汽腔室上游,用于控制调节来自于锅炉的高温高压蒸汽。在电站实际运行过程中,阀门系统中的主汽阀和调节阀都有着明确的分工:主汽阀一般处于全开状态运行,仅在汽轮机系统出现紧急事故需要立刻停机时才会迅速关闭;而调节阀则需要经常改变开度以调节汽轮机蒸汽流量大小,以适应汽轮机组经常变化的功率输出要求。阀门系统的复杂结构以及紧凑的布置方式等,无疑会导致高温高压的过热蒸汽在流入超超临界汽轮机阀门后,而形成极度紊乱的蒸汽流动特征。尤其是调节阀在中小开度运行下的节流效应,更会导致阀门下游管道内的蒸汽流场极度不稳定,甚至会影响汽轮机组的安全运行。因此,对超超临界汽轮机阀门内的非定常流动特性进行全面深入的探究是非常重要和迫切的。本文将国内某1000MW超超临界二次再热机组中的汽轮机阀门作为主要研究对象。主要研究点包含:主汽阀滤网层对阀门流场的影响、阀门时均流场分布特征、阀门壁面附着流动与分离流动的非定常特性以及阀门暖机工况的汽流激振分析等。基于此,将采用剪切应力输运模型(Shear Stress Transport,SST)、分离涡模拟(Detached Eddy Simulation,DES)分别对阀门内的时均蒸汽流场和非定常蒸汽流场进行数值计算和分析。开发和建立涵盖本征正交分解(Proper Orthogonal Decomposition,POD)、时空互相关分析(CrossCorrelation Analysis)和声学模态分析(Acoustic Modal Analysis)的先进流体分析体系。该体系将针对数值计算得到的海量流场数据进行科学处理和分析,以揭示超超临界汽轮机阀门中典型流动结构,如壁面附着流动与壁面分离流动等的非定常特性以及声学模态响应特性等。为了分析主汽阀滤网层对超超临界汽轮机阀门时均流场分布特征的影响,本文首先搭建了阀门滤网循环水槽实验台,验证滤网指向性多孔介质模型的准确性,最后对比分析了安装滤网前后的阀门流场分布特征。研究发现:当汽轮机调节阀全开运行时,滤网具有强烈的整流效应,使得主汽阀内部流场趋于均匀和稳定;当调节阀开度降低时,滤网对阀门流动分布特征的影响越来越低,尤其是当调节阀开度低于28%时,滤网的存在与否几乎没有影响。为了分析调节阀在不同开度和背压下的时均蒸汽流场分布特征,首先搭建了阀门高压气动实验台,以调节阀通流特性和阀内压力分布特性为标准,评估SST模型计算调节阀时均流场的准确性;最后对蒸汽阀门的时均流场进行系统的计算和归纳分析。结果表明:当调节阀背压较高时,阀内蒸汽流场呈现壁面附着流动的分布特征;当调节阀背压低于临界分离压比时,阀内流场则呈现壁面分离流动的分布特征。此外,深入的分析表明调节阀壁面附着流动和壁面分离流动的形成主要受Coand?效应的影响;并会受到膨胀波、压缩波的影响而使得流场出现离散的“膨胀再压缩区域”。为了分析阀门壁面附着流动与壁面分离流动的非定常特性,首先搭建了阀门高压气动实验台,以阀内压力波动的幅值和频率信息为标准,评估DES方法计算调节阀非定常流场的准确性;随后分别对调节阀的壁面附着流动和壁面分离流动进行非定常DES计算;最后将POD分析、时空互相关分析和声学模态分析等应用到调节阀非定常流场的后处理分析中。结果表明:主导调节阀内流场非定常波动的主要因素是壁面附着或壁面分离流动的交替振荡行为;并由此而导致了阀门内的轴向压力脉动、侧向压力脉动等,从而引起了调节阀阀杆所受气动力的轴向波动和侧向波动等。结合阀门声模态分布,可以发现调节阀一阶径向声模态以及轴向声模态等可能与流场中的相干结构或压力脉动模态相互耦合,从而引起较强的气动噪音问题。最后,本文将已经建立的阀门气动特性分析体系应用到汽轮机阀门在工况下的汽流激振分析中,揭示了诱导阀门振动和噪音的流体激励源和声学激励源。采用DES模拟计算该工况下的非定常流场,提取阀杆气动力波动的频率信息。发现其与电厂实地测量的阀杆振动频率几乎一致,说明了阀杆振动主要是气动力波动引起的。采用POD分解对调节阀的压力脉动场和速度脉动场进行分解,提取出主导压力脉动和速度脉动的湍流相干结构,发现主导调节阀内流场侧向波动的湍流相干结构是由壁面附着流动的交替振荡而引起的,而主导流场轴向波动的湍流相干结构是由壁面附着流动的同步振荡而引起的。同时发现调节阀阀杆轴向气动力在St=0.174频率下的波动和调节阀内St=0.19的轴向声模态相互耦合,调节阀阀杆侧向气动力在St=0.62频率下的波动和调节阀内St=0.61的一阶径向声模态相互耦合。更多还原

【Abstract】 The ultra-supercritical(USC)power generation is the most advanced technology in modern coal-fired power plant,due to its safety operation,unit durability and high efficiency.As the important control system of the ultra-supercritical steam turbines,the steam turbine control valves are commonly used to regulate the mainstream steam flow for the thermal power plants.The control valves are generally integrated by a main valve and a throttle valve in sequence.The main valve is used to keep the safety of the whole steam turbine system by rapidly cutoff the steam supply in emergency;and the throttle valve has to work under wide conditions to adjust to the variant output power of thermal plants.In practice,the mainstream steam flow with high pressure and high temperature could bring additional thermal stresses to the control valves.In addition,the compact configuration of the main valve and throttle valve would creat a complicated serpentine flow passage,may induce a highly unstable steam flow to the control valves.Even worse,the steam flow pattern of control valves can be various with the valve’s open ratio and pressure ratio by considering the wide range of operation conditions.Previous studies had classified the valve’s flow patterns into two categories,i.e.the attachment flow and detachment flow;which were always accompanied with the unstable flow structures such as the rotating pressure fluctuations,the impingement of shear flow,flow separations and reattachments.The unsteady flow behaviors of these flow structures can also be coupled with valve’s acoustic modes,inducing to intensified noise;coupled with valve’s structural modes,inducing to structural vibrations or even operational risk.Consequently,further understanding of the unsteady flow behaviors inside the control valves is of great practical significance to the effective operation management.This paper focused on the unstable steam flow of the control valves in a domestic ultrasupercritical steam turbine unit with second reheat.The time-averaged steam flow patterns and time-variant steam flow behaviors inside the control valves are captured with the Shear Stress Transport(SST)and Detached Eddy Simulation(DES)turbulence model,respectively.Based on the advanced analysis methods,which contain with the Proper Orthogonal Decomposition(POD),spatial and temporal cross-correlation analysis and acoustic modal analysis,the huge amounts of numerical data were deep excavated and analyzed,revealing the vortex dynamics and the acoustic response of the unsteady attachment and detachment flow inside the control valves.Towards this end,four research points were conductued in present study,i.e.influence of strainer on valve’s time-averaged flow patterns,classification of valve’s time-averaged flow patterns,unsteady flow behaviors of valve’s attachment and detachment flow,validation on the flow-induced valve’s vibrations at the steam turbine’s warmup condition.To reveal the influence of the circular strainer on the flow patterns of steam control valves,a water flow test rig was built to validate the strainer porous model,which established the dependencies of the pressure drop through the strainer on the magnitude and direction of the mainstream flow’s velocity.As the benchmark configuration,a valve without a strainer was used for comparison.The turbulent steam flow in the complex serpentine channel was simulated with the implementation of the proposed porous model for the strainer.The numerical results demonstrated that placing the strainer in the main valve resulted in dramatic changes of the flow patterns in the main valve’s chamber and its diffuser,and even in the downstream throttle valve.The complex steam flow in the main valve was efficiently managed by the circular strainer especially at the fully opening of throttle valve;this is attributed to attenuated oscillation of the annular flow around the main valve’s seat.However,the influence of strainer on the valve’s flow pattern became weak at the small opening of throttle valve.Therefore,the configuration of strainer or even the main valve was removed to save the numerical cost in the subsequent simulations of throttle valve at small opening ratios.To classify the time-averaged flow patterns of the control valve corresponding with variant opening ratio and pressure ratio,a high pressure valve test rig was built to validate the ability of SST model to compute the valve’s flow characteristic and pressure profile.Subsequently,the valve’s attachment flow was identified with higher back pressure;while the detachment flow was captured when the back pressure was smaller than the critical detachment pressure.Furthermore,deep understanding showed that the transition from valve’s attachment flow to detachment flow was closely related with the Coand? effect and the jet’s expansionrecompression processes.Following the identifications of the time-averaged flow patterns,the DES simulations were performed to capture the unsteady flow behaviors corresponding with the attachment and detachment flow,respectively.Another high pressure valve test rig was especially built to evaluate the ability of DES model to capture the amplitudes and frequencies of the pressure fluctuations.Additionally,the POD analysis,cross-correlation analysis and acoustic modal analysis were performed on the numerical flow fields,indicating that: the alternating oscillations of wall-attached-jet or wall-detached-jet dominated the fluctuated flow fields of valve,resulting in the axial pressure modes and lateral pressure modes,which can act on the valve’s spindle and induce the valve’s axial vibrations and lateral vibrations.Moreover,the axial acoustic modes and the first circumferential acoustic mode were confirmed coupling with the unstable flow fields,which could no doubt lead to extensive noise.Finally,the flow-induced valve’s vibrations at the wamup condition during the steam turbine’s cold state startup,were comprehensively analyzed by using the combinatory method which contains with DES simulation,POD decomposition method,cross-correlation method and acoustic modal analysis.The fluctuation frequencies of valve’s aerodynamic forces were extracted from the DES resolved unsteady steam flow.By comparison with vibration frequencies of valve’s field measurements in power plant,it was concluded that the valve’s vibrations were directly induced by the fluctuated forces.The results demonstrated that the control valve’s axial vibration at St=0.174 was related with the axial acoustic mode in valve’s cavity,and the cavity shear layer oscillations were found as the flow excitation source;however,the lateral vibration at St=0.62 was associated with the first circumferential mode of control valve,and the periodical pressure fluctuations generated by the turbulent mixing process were confirmed as the flow excitation source.By POD analysis,the first two POD modes occupied about 25% energy of the turbulent fluctuation,corresponding to valve’s lateral vibration at St=0.019,were found resulting from the alternating oscillations of the annular wall-attachedjet.Simultaneously,the modes 3,4 and 5 occupied about 15% energy of the turbulent fluctuation,corresponding to valve’s axial vibration at St=0.043,were found resulting from the synchronous oscillations of the annular wall-attached-jet.更多还原