紊流状态下轴承失稳转速的迭代计算法

本文的目的是通过二个φ450试验轴承(双侧供油、上瓦不开槽、沟的椭圆轴承和三油楔轴承)的静、动特性计算,把计算结果与全尺寸大型滑动轴承试验台上得出的实测值进行比较分析,讨论了紊流因子对计算性能的影响.特别分析了影响动力特性计算结果的几个主要因素.从而解释了在理论依据基本一致的前提下,造成动特性计算结果差异的原因.我们认为,在紊流状态下,动特性系数的计算迭代是影响失稳转速理论值的主要因素,而紊流因子的差异并不是造成失稳转速具有不同计算值的真正原因.在上述基础上,提出在产品设计中以轴承动特性裕度较大为目标的紊流因子选择和计算过程中应完成的迭代要求.     

基于支持向量回归的大容量机组主蒸汽流量建模

分析了大容量机组主蒸汽流量的计算原理,指出了常规的基于调节级后压力计算模型的弊端.介绍了支持向量回归计算模型及其参数选择,并将该模型应用于某300MW机组的主蒸汽流量建模计算,同时与RBF神经网络模型进行对比.结果表明,基于支持向量回归的计算模型不仅能够在不同工况下对主蒸汽流量进行准确估算,还能够适应机组通流部分状态发生改变时主蒸汽流量的计算,并具有较好的泛化能力和稳定性,适于在线计算,能够满足机组经济性诊断实时计算的要求.     

风电机组载荷计算标准的对比研究

基于GH Bladed软件,以某ⅢA直驱型风电机组为计算模型,分别采用GL 2010和IEC 2005两种标准进行载荷计算,并分析两种标准下的输入参数、计算工况、极限载荷及疲劳载荷计算结果的差异。分析表明,对于极限载荷,叶根、轮毂大部分的载荷分量,依据IEC 2005标准计算的结果较大,而塔架和偏航轴承部位的大部分载荷分量,使用GL 2010标准计算的结果更大。分析认为,极限载荷的差异是风况条件、计算方法及统计方式的不同造成的;疲劳计算结果差异不明显。为了更好模拟风场条件,并获得统计特性更加稳定的载荷结果,该文推荐使用IEC 2005标准。     

改进型椭圆轴承特性分析

介绍一种底部内嵌圆弧的改进型椭圆轴承.采用动压润滑理论,计入紊流及温粘效应,对其静、动特性进行了计算分析,对计算结果进行了验证.通过与传统椭圆轴承的对比分析计算,显示该轴承具有更优的性能.     

汽轮机组热耗率指标计算基准流量筛选方法

汽轮机常规性能试验时,一般不额外加装流量测量装置,多直接使用现场流量测量装置。由于现场流量测量装置准确性未知,经常会出现采用不同基准流量计算所得的热耗率指标结果迥异的现象,困扰着试验人员对机组性能的评价。引入冗余流量测量、耗差分析等机组附加信息,提出了热耗率指标计算基准流量的筛选方法。通过对实际机组的计算,证明了方法的有效性。     

可倾瓦轴承动态特性计算模型及方法研究

可倾瓦轴承由于具有良好的制振性及高稳定性等特征,目前被广泛应用于各种旋转机械。但由于可倾瓦轴承瓦块的摆动性,增加了系统的自由度,所以可倾瓦轴承线性动力系统的建模及计算方法较之固定瓦轴承要复杂的多。根据建模方法的不同,可倾瓦计算模型主要分为常规八系数模型、频变八系数模型、完整动力学系数模型3种。结合某引进机组大型可倾瓦轴承为研究对象,对可倾瓦轴承动态特性3种计算模型及方法进行了研究。并对计算中不计热弹变形及考虑热弹耦合效应下的轴承常规八系数动特性进行了计算,并对频变八系数模型进行了分析计算。结果表明:考虑瓦块热弹变形的可倾瓦轴承动特性系数计算结果精度较高,取消瓦块摆动频率与转子转频相同的假设的模型可望获得更高的精度。     

汽轮机组基于弹性基础下轴系稳定性的评估

采用弹性基础的汽轮机组,其基础静刚度及动刚度相较于刚性基础均有所下降,易产生轴承标高变化和轴系失稳的风险。因此,基于弹性基础下轴系稳定性的研究对于保障机组运行的安全性和稳定性具有十分重要的意义。在轴系稳定性核算中准确考虑基础刚度的耦合作用是必要的,研究中将不同频率下的基础刚度和对应的轴承支撑刚度与油膜刚度进行耦合,形成整个支撑系统的动刚度,进而更加真实地计算机组轴系稳定性结果。     

660MW机组配汽方式对轴系稳定性的影响

汽轮机在部分负荷时的调节配汽特性不仅影响轴系稳定性,而且还影响机组运行经济性。该文以某电厂660MW超临界机组为例,应用CFD技术,建立了调节级叶片汽流力计算模型,并分别对原阀序和优化阀序进行了不平衡汽流力与轴承载荷的分析计算,并在机组运行中得到了应用。     

预混合燃烧现象学紊流火焰速度模型

提出了一个用于预混合燃烧的现象学紊流火焰速度模型,描述了火焰从层流传播到充分发展的紊流传播的全过程。基于火焰瞬时尺度和基本的紊流特性参数,按照火焰生长的各个阶段,将紊流火焰速度的计算分为３个步骤,以有效紊流强度显示从层流传播到紊流传播的转化,以紊流积分标尺和梅尔莫哥洛夫标尺作为火焰皱折程度的度量,考虑了火焰表面扭曲对火焰速度的作用。计算结果与测量数据的比较显示了较好的一致性。     

山区河流阶梯—深潭结构水力特征数值模拟

为了探究阶梯—深潭结构在不同流量工况下的消能机理,采用紊流数值模拟方法分析研究了阶梯—深潭结构紊动能、紊动能耗散率、流场结构、潭底压力强度等主要水力参数。结果表明,随着流量的增大,平均紊动能耗散率不及平均紊动能增加速率快,验证了阶梯—深潭随着流量的增加消能率会有所下降;小流量工况下深潭内环流区明显,增大了水流滞留潭区时间,能量耗散效果较优;大流量工况下流量的增加促使结构发生自适应调整,水深加大,形成水垫及漩滚耗能,水流阻力增大且维持潭底压差分布趋于平稳,削弱了主流对河床的直接冲刷,有利于河床稳定。     

Wind turbine main‐bearing loading and wind field characteristics

This paper investigates the relationship between wind turbine main‐bearing loads and the characteristics of the incident wind field in which the wind turbine is operating. For a 2‐MW wind turbine model, fully aeroelastic multibody simulations are performed in 3D turbulent wind fields across the wind turbine's operational envelope. Hub loads are extracted and then injected into simplified drivetrain models of three types of main‐bearing configuration. The main‐bearing reaction loads and load ratios from the simplified model are presented and analysed. Results indicate that there is a strong link between wind field characteristics and the loading experienced by the main bearing(s), with the different bearing configurations displaying very different loading behaviours. Main‐bearing failure rates determined from operational data for two drivetrain configurations are also presented.     

Modified theoretical models of film condensation in horizontal microfin tubes

The previously proposed theoretical models of film condensation in horizontal microfin tubes have been modified to describe the characteristics of condensing two-phase flow more accurately. The stratified flow regime and the annular flow regime were considered. For the stratified flow regime, the previously proposed theoretical model was modified to take account of the curvature of stratified condensate due to the surface tension force. For the annular flow regime, a more accurate expression for the interfacial shear stress was incorporated. Generally, the modified theoretical models predicted a lower circumferential average heat transfer coefficient than the previously proposed ones. Comparison of the theoretical predictions with available experimental data for six tubes and five refrigerants revealed that a good agreement (r.m.s error of less than 21.1%) was obtained for all cases when the higher of the two theoretical predictions were adopted as the calculated value.     

风力机叶片S832翼型的两种湍流模型数值分析方法及其比较

采用S-A和RNGK-ε湍流模型对风力机专用S832翼型的绕流流动建立了二维不可压缩湍流模型,利用计算流体力学软件Fluent,对两种模型进行数值模拟,得到了雷诺数为3×10^6时该翼型在-16°～30°攻角下的升力系数和阻力系数与来流攻角的关系以及压力分布图,并进一步分析了不同攻角下翼型表面压力分布特性,预测了大攻角（达30°）下翼型分离流动特性。结合NREL的试验数据,对两种湍流模型模拟的精度进行了分析比较,结果表明在小攻角范围内采用RNGK-~模型预测该翼型气动性,其结果更加有效。     

基于两种湍流模型的某风机专用翼型数值研究

针对风力机专用S832翼型绕流流动建立了二维不可压缩湍流模型,利用计算流体力学软件Fluent,分别选用S—A、RNGk-ε两种湍流模型对S832进行数值模拟,对比了两种湍流模型对气动模拟精度的影响,得出了雷诺数为3×10^6时,该翼型在-16°～30°攻角下的升力系数和阻力系数随来流攻角的变化关系及压力分布图,分析了不同攻角下翼型表面压力分布特性并进一步预测了大攻角（达30°）下翼型分离流动特性．并与NREL的试验数据进行比较,研究结果表明：RNGk—ε在预测该翼型小攻角范围气动性方面更加有效。     

How can a wind turbine survive in tropical cyclone?

This study presents the external wind conditions for the design and assessment of wind turbine loading in tropical cyclone regions, including physical constants, wind speed (cyclone classes), wind shear, turbulence intensity, turbulence length scale and turbulence spectral models. For the extreme condition, this study focuses on the wind characteristics of the cyclone eye-wall region that carries the strongest wind. For the dynamic response of wind turbine structures, it is worth the effort to characterize the size of eddies constituting turbulent wind. The turbulence integral length scale for cyclone wind is defined and validated with various measurements. Moreover, several turbulence spectral models are validated with field measurements and the ESDU von Karman model gives the best fit. Based on the external wind conditions, a new turbulent cyclone wind model is created with the associated load case(s). A state-of-the-art load analysis is performed using this new cyclone wind model and the results for the relevant turbine components are compared with the existing loads envelope.     

A level set formulation for premixed combustion LES considering the turbulent flame structure

In this paper, a consistent and rigorous formulation is developed for the coupling of the G-equation model to an LES flow solver that describes the interactions of the scales of the flame, the turbulence, and the filtering procedure from the resolved turbulence regime to the broadened preheat regions regime. A progress variable equation is introduced to describe the filtered flame structure. The models provided for the sub-filter diffusivity and the filtered reaction term appearing in this equation are consistent with the solution of the G-equation model. The solution of the progress variable equation ensures that the resolved part of the turbulent mixing in the preheat region can be described. However, the C-field is underresolved if the sub-filter Damköhler number is not much smaller than unity, and hence the solution of the C-equation cannot be expected to produce the correct flame propagation speed. The coupling with the G-equation ensures that the flame front described by the filtered reaction progress variable moves with the correct propagation velocity, independent of numerical diffusion caused by an underresolution of the flame. Formulations both for low-Mach number flow solvers and for fully compressible solvers are presented. To validate the formulation, the model is applied in compressible LES of two turbulent flames anchored by a triangular flame-holder. For the statistically stationary case, the mean and RMS progress variable are in very good agreement with experimental data, demonstrating that the model correctly reproduces the flame anchoring and the flame-turbulence interactions in the recirculation zone. For the acoustically pulsed case, the LES fields show the same large scale fluctuations that are present in the experimental data.     

600MW超临界煤粉炉燃烧过程数值模拟

四角切圆煤粉锅炉是我国较为普遍适用的燃煤锅炉的炉型之一,炉膛结渣是影响锅炉圆燃煤锅炉膛内的湍流流动,传热和燃烧过程进行了三维数值模拟,得出炉膛内温度场和速度场分布。通过灰污层外表面平均温度与煤灰的变形温度DT进行比较,能够较为准确地判断结渣区域,为安全运行提供有效依据。     

Stability of two-phase stratified flow as controlled by laminar/turbulent transition

Flow pattern transition from stratified-smooth to stratified-wavy has been usually identified with a condition of neutral stability, where destabilizing effects are due to the inertia of the two-phases. It is shown that this is indeed the case when instability is approached with laminar gas phase. However, when the upper gas phase is turbulent, a destabilizing term appears due to dynamic interaction of the turbulent flow with the perturbed free interface. At the transitional range from laminar to turbulent flow regime the evolution of wavy pattern is not predicted by stability condition and coincides with the laminar/turbulent flow regime transition.     

Cascaded collision lattice Boltzmann model (CLBM) for simulating fluid and heat transport in porous media

The present paper reports a cascaded collision lattice Boltzmann model for the simulation of an incompressible two-dimensional fluid flow in a porous media regime. The cascaded model is first validated for the nonporous regime using limiting conditions against previous finite element model reports. Subsequently, the cascaded collision model is applied to the lid-driven porous-filled cavity to demonstrate the largely augmented numerical stability of the model against the more common Bhatnagar–Gross–Krook and multiple relaxation time collision models. Finally, the cascaded model is applied to an inflow–outflow case of flow and heat transfer over a porous bluff body to showcase its efficiency in capturing the complex fluid and heat transport phenomenon through porous media.     

Heat transfer and friction in the offset stripfin heat exchanger

This paper presents analytical models to predict the heat transfer coefficient and the friction factor of the offset strip-fin heat exchanger surface geometry. Two flow regimes are defined—laminar and turbulent. Based on the conditions in the wake, an equation is developed to predict transition from laminar to turbulent flow. Flow visualization experiments were performed to identify the flow structure at transition. The condition predicted by the transition equation corresponds to onset of oscillating velocities in the fin wakes. Equations are developed for the Nusselt number and friction factor by writing energy and momentum balances on a unit cell of the offset strip-fin geometry. A numerical solution is used to calculate Nu and f on the fins in the laminar regime, and a semi-empirical approach is used for the turbulent regime. Predictions are compared to data on scaled-up geometries, taken in the present study, and data on actual heat exchangers. The models predict all data within ±20%.