悬臂止推箔片轴承三维流-固-热耦合数值分析

工作温度是影响轴承性能关键因素之一,为了深入分析轴承气膜温度变化对箔片轴承承载特性的影响,本文中建立了考虑冷却气实际流动特性的悬臂止推箔片轴承三维流-固-热耦合模型,研究了轴承间隙、转速以及冷却气流速变化时悬臂箔片轴承气膜压力场和温度场等的变化规律.研究结果表明：随着轴承间隙减小以及轴承转速增大,气膜表面温度逐渐升高,其中气膜高压区温度上升更快,气膜温度与轴承间隙呈现线性变化趋势,气膜温度与转速呈现非线性增长的趋势,相比于轴承间隙,轴承转速升高对润滑气膜温度场影响更大,气膜温度过高可能会造成轴承热失效,因此需要深入研究工作温度对轴承性能的影响;随着冷却气流速增大,轴承承载力和气膜温度逐渐减小.冷却气流速增大到一定程度时,降温效果不再发生明显变化.     

不同箔坝位置关系下浮动坝箔片端面气膜密封性能研究

提出一种具有浮动密封坝的箔片端面气膜密封(FSD-CFFGS),并以此为研究对象建立密封气弹耦合润滑理论模型,采用有限差分法求解可压缩气体的雷诺方程,分别在箔片端面高于、等于和低于密封坝平面三种关系下系统研究支撑箔柔度系数对膜压、形变及密封性能的影响规律,探究FSD-CFFGS的工作原理和密封机理.综合考虑自适应性、开启性和控漏性,确定FSD-CFFGS支撑箔柔度系数优选范围.结果表明：当箔片端面高于密封坝平面时,密封流体动压效应显著,开启性能较好;高度差Δh取1.5～2.5μm、箔片区支撑箔柔度系数α₁取0.05～0.15、浮动坝区支撑箔柔度系数α₂取10^-5～10^-3时,FSD-CFFGS具有一定自适应能力并能保证较好的开启性和控漏性.     

用热膜风速仪对气膜冷却流场湍流强度的测量

一、前言平板气膜冷却流场里,主流和射流混合后,形成半壁射流的内外两个混合边界。如图1所示。主流和射流的初始湍流强度直接影响两股气流的掺混程度。因而影响了气膜冷却的效率和气膜层的稳定性。近年来,人们开始研究用降低湍流强度的方法,提高气膜冷却效率的可能性。研究湍流强度对气膜冷却效果的影响是有意义的。朱哈茨和马雷克(Juhasz—Marek,      

支点变形对水润滑可倾瓦推力轴承起动过程影响

本文中建立了水润滑可倾瓦推力轴承启停过程瞬态模型,采用Hertz接触模型,以自定义可倾瓦推力轴承起动过程发生初始倾斜时刻转速—初始倾斜转速Uft为对象,分析了支点接触与磨损变形量、载荷大小对水润滑可倾瓦推力轴承起动过程影响.初始倾斜转速Uft随着支点变形量增大而增大,随着载荷增大而增大.在给定可倾瓦推力轴承可接受初始倾斜转速最大值Uftc情况下,几何尺寸确定可倾瓦推力轴承载荷及支点变形均存在最大值.采用水润滑可倾瓦推力轴承性能试验台进行模型验证,结果表明:Uft测量值与数值分析结果吻合度较高,误差小于10%;采用加速度传感器及扭矩传感器联合方法可以比较准确地判断出轴承推力瓦发生倾斜时刻,从而确定可倾瓦推力轴承的Uft值.     

推力轴承瞬态启动油膜热不稳定性的线性分析

以简化推力轴承为对象 ,理论上证明了推力轴承运行时存在热不稳定性 ,采用小扰动分析法得到了油膜温度的扰动方程 ,应用简正模态分析法推导了无量纲热不稳定性准则数以及推力轴承运行的热不稳定性准则 .     

气膜孔径向角角度对冷却效率的影响

为了探讨在不同径向角下动量比和湍流度对圆柱形气膜孔流动和换热的影响规律,采用数值模拟方法,研究了涡轮叶片的冷却效率.结果表明:随着动量比的增大,二次流出口处高温区域逐渐偏离气膜孔出口叶片的下游区域,气膜孔出口二次流的影响范围变大;二次流径向角β越大,其自气膜孔出口流出后在叶片表面的轨迹偏斜程度就越大;在湍流度保持不变的情况下,随着动量比增加,冷却效率随着x/d值的增加在总体上呈现逐渐减小的趋势;随着湍流度的增大,冷却效率先增加后减小;在动量比I≤2时,冷却效率随着湍流的增大而减小;随着径向角的增大(0°～45°范围内),冷却效率逐渐降低.     

箔片-电磁混合轴承的稳态承载特性及控制

箔片-电磁混合轴承(HFMB)是一种将气体箔片轴承和电磁轴承混合使用的新型轴承,有效解决了气体箔片轴承低速磨损大和电磁轴承承载力有限的不足,并且具备载荷可分配和支撑系统动力学性能可调节等优点.文中在分析两种轴承稳态承载特性的基础上详细讨论了混合轴承的稳态控制方法,给出了一种以电磁轴承实际承载力与预分配承载力差值最小为控制目标,通过等边三角形为基本单元对混合轴承工作区域进行划分的箔片-电磁混合轴承稳态工作位置搜索算法.最后建立了系统模型并进行了数值仿真,验证了稳态控制系统的可行性和有效性.     

热耗散下螺旋槽干气密封气膜刚度的计算与分析

通过二阶非线性滑移边界条件下的雷诺方程并用PH线性化方法和迭代法求得螺旋槽内的气膜推力和气膜压力,并推导了其气膜厚度,得到二阶非线性滑移边界条件下气膜刚度的近似解析式,推导出考虑热耗散下的气膜能量微分方程;利用气膜的压力、能量方程、二阶非线性滑移边界条件下气膜刚度的近似解析式,通过Matlab软件求得螺旋槽内气膜刚度在不同压力、转速、槽深、螺旋角下的分布。结果表明:随着压力、转速、槽深的增大,气膜刚度随之增大,并在槽根部附近达到最大值,且气膜刚度的变化呈非线性;在槽深为6μm、介质压力为0.4MPa、转速为8700r·min-1、环境压力为101.3k Pa的工况下,螺旋角为75°左右时,气膜刚度最大。通过本文设计的在不同介质压力下的试验表明,通过能量微分方程计算所得的考虑热耗散下的气膜刚度数值比不考虑热耗散的气膜刚度数值更接近试验值。本文结果对优化干气密封结构参数、提升干气密封性能十分重要。     

大型抽水蓄能机组推力轴承特性研究——（Ⅰ）静特性研究

为了精确计算可倾瓦推力轴承的静特性,本文建立了推力轴承静特性的计算模型,推导了推力轴承动力润滑的基本Reynolds方程,考虑了润滑油温粘效应、素流的影响、瓦块的温度变形及压力弹性变形．本文还以广州蓄能水电厂一期工程四号机组的推力轴承为例,计算了几种不同初始参数条件下的计算结果,以期对机组推力轴承的特性有一个较全面的认识和了解．     

气膜冷却火焰筒壁温和热流量计算机程序

一、前言燃气轮机的进口温度和进口压力不断提高后,火焰的的壁面温度和热流量相应增加,火焰筒的气膜冷却任务加重,用于火焰筒的气膜冷却空气量愈是感到不足。因此,降低湍流强度,提高气膜冷却效率;合理设计气膜冷却段的长度和缝高;验算火焰筒的壁温分布和延长火焰筒的使用寿命是近代燃气轮机设计中的一项重要课题。      

局部多孔质气体静压轴向轴承静态特性的数值求解

运用数值方法分析局部多孔质节流气体静压轴向轴承的静态性能,分别建立局部多孔质圆柱塞内的压力分布方程和气体薄膜内的压力分布方程,利用坐标变换将局部多孔质圆柱塞的圆柱坐标与气体薄膜的圆柱坐标转换到同一笛卡儿坐标系,为有限元离散奠定基础.经过有限元推导,求得局部多孔质气体静压轴向轴承的承载能力与静态刚度,并对局部多孔质节流进行试验以验证理论模型的正确性.另外,对局部多孔质节流气体静压轴向轴承和小孔节流气体静压轴向轴承进行对比试验.结果表明:局部多孔质节流和小孔节流静压轴承的承载能力随着气膜厚度的减小而增加;静态刚度随着气膜厚度的增加先增加后减小;局部多孔质节流比小孔节流具有较高的承载能力和静态刚度.     

带冷却气流的亥姆霍兹共振器的声类比模型

亥姆霍兹共振器(HR)作为典型的被动消声装置,常被安装于航空发动机和燃气轮机的燃烧室上用以吸收噪声进而抑制燃烧热声振荡.在实际应用中,为防止燃烧室内高温气体损坏HR,常引入冷却气流从HR的背部空腔通过其颈部流入燃烧室,以保护HR.该冷却气流的温度一般显著低于燃烧室内的燃气温度.将这样的HR安装到燃烧室上时,该温差可能影...     

碟形弹簧支承圆形瓦推力轴承热动力润滑性能分析

对碟形弹簧支承圆形瓦推力轴承在稳态运行时的热动力润滑性能进行了分析研究,考察了弹簧弯曲刚度,载荷和转速对轴承的油膜厚度为分布,压力分布,温度分布,功耗及油膜压力中心位置的影响,并提出了温度因子概念,研究表明,较小的弹簧弯曲刚度和载荷有利提高轴承的热动力润滑性能,油膜温度随温度因子的增大而增大,当轴承转速在较大的范围内变化时,温度因子基本为常母,油膜温度敢基本不变,油膜压力中心位于瓦几何中心的上游区     

运行过程中载荷突变时可倾瓦推力轴承瞬态热效应的实验研究

研究了可倾瓦推力轴承在名义转速分别为2000r/min和4000r/min下,当载荷突然变化时推力轴在油膜温度和油膜厚度的瞬态变化规律。实验结果表明：当载荷突然增大时,油膜温度以及进油边温度上升,油膜厚度减小;随着载荷变化幅度的增大,温度上升幅度也增大,油膜厚度进一步减小;在载荷变化相同的情况下,相同时间间隔内转速高时油膜温度增大幅度比转速低时要大,而油膜厚度减小幅度比低转速下小。     

螺旋槽端面微间隙高速气流润滑密封特性

考虑入口气流压力损失和出口阻塞效应,建立了微间隙端面高速气体润滑密封分析数学模型,对螺旋槽端面微间隙高速气流润滑密封特性进行研究.重点分析了不同密封间隙、密封压力和转速等工况条件下,入口压力损失和出口阻塞效应对开启力、泄漏率及气膜刚度等密封特性参数的影响规律.结果表明:高速气体阻塞效应使出口压力高于环境压力,压力损失使入口气膜压力下降,导致泄漏率和气膜刚度明显下降,并使开启力增加.随着密封压力和密封间隙的增加,阻塞效应增强,导致泄漏率和气膜刚度显著降低.密封压力10 MPa时,泄漏率降低可达20%,气膜刚度的下降可达30%以上.     

Heat transfer measurements in fully turbulent flows: basic investigations with an advanced thin foil triple sensor

In a former article in this journal a double layer hot film with two 10 μm nickel foils, separated by a 25 μm polyimide foil was introduced as a multi-purpose sensor. Each foil can be operated as a (calibrated) temperature sensor in its passive mode by imposing an electric current small enough to avoid heating by dissipation of electrical energy. Alternatively, however, each foil can also serve as a heater in an active mode with electric currents high enough to cause Joule heating. This double foil sensor can be used as a conventional heat flux sensor in its passive mode when mounted on an externally heated surface. In fully turbulent flows it alternatively can be operated in an active mode on a cold, i.e. not externally heated surface. Then, by heating the upper foil, a local heat transfer is initiated from which the local heat transfer coefficient h can be determined, once the lower foil is heated to the same temperature as the upper one, thus acting as a counter-heater. For further investigations with respect to the underlying sensor concept a triple sensor has been built which consists of three double layer film sensors very close to each other. Various aspects of heat transfer measurements in active modes can be addressed by this sensor.     

碟形弹簧支承圆形瓦推力轴承 热动力润滑性能分析

The steady-statethermohydrodynamic lubrication p erformance of thrust bearing with plate-spring supported circular pads was stud ied.Ananalysis of influence of spring flexure rigidity,load, and angular speed on the distribution of film thickness, film pressure, filmtemperature,power l oss, and pressure center location was carried out.It is shown that low flexure r igidity of spring and load ishelpful in enhancing the lubrication performance o f thrust bearing. A concept of temperature factor is presented as well. Thetemp erature factor keeps almost unchanged in a wide range of angular speed, the cor responding change in the filmtemperature is negligible. Moreover,the pressure c enter of oil film is located at the upriver range of the circular pad.     

Convective heat and mass transfer from a falling film to a laminar gas stream

A numerical study has been made of convective heat and mass transfer from a falling film to a laminar gas stream between vertical parallel plates. The effects of gas-liquid phase coupling, variable thermophysical properties, and film vaporization have been considered. Simultaneous mass, momentum and heat transfer between liquid film and gas stream is numerically studied by solving the respective governing equations for the liquid film and gas stream together. The influences of the inlet liquid temperature and liquid flowrate on the cooling of liquid film are examined for air-water and air-ethanol systems. Results show that the heat transfer from the gas-liquid interface to the gas stream is predominantly determined by the latent heat transfer connected with film evaporation. Additionally, better liquid film cooling is noticed for the system having a higher inlet liquid temperature or a lower liquid flowrate.     

超导磁力与静压液膜力复合轴承的静动特性分析

以新一代液体火箭发动机涡轮泵为应用前景,提出了一种带小孔节流的超导-液体静压复合推力轴承.该复合轴承由6块圆形超导瓦和6块带有小孔节流的圆形液体静压推力瓦构成,依靠涡轮泵系统自带的低温介质(如液氢液氧等),可以实现超导磁斥力与流体静压力的复合.基于解耦方法分析了复合轴承的静动特性,重点研究不同液膜厚度下复合轴承的承载力和刚度随节流孔径、液腔直径等的变化规律.在设计工作点附近,超导推力瓦和静压推力瓦的承载力大体相当,而后者的刚度则是前者的300倍以上.理论结果表明该复合结构既可以保证启动阶段无接触摩擦,又能在工作阶段保持较高刚度以抗冲击,对设计高可靠性火箭涡轮泵的轴系结构具有参考价值.     

Numerical methods for theoretical analysis of foil bearing dynamics

The bearing under consideration is a self-acting, gas bearing with a flexibly supported foil. In order to conduct the theoretical analysis, three systems were identified: a rotor, a gas film and a flexible structure. Each of these elements has been mathematically analysed and analytical equations have been formulated. It was found, that the gas flow in the bearing can be described by the Reynolds equation, whereas a spring-damper model was selected for the structural analysis. The Reynolds equation is a differential equation the exact solution to which is unknown. The work describes the finite difference method in detail, where the partial derivatives in the Reynolds equation are replaced by a system of algebraic equations. In order to solve the resulting system, the Alternating Direction Implicit method (ADI) was used. Based on that and on the analysis of interactions between the three systems the equations have been computed. The accuracy of methods has been verified by means of series of numerical tests. Chosen results are described in this paper.