液体混压油膜轴承润滑机理及分析

以雷诺方程和流量连续方程为基础建立了液体动静压轴承润滑机理的基本模型,利用有限差分法来求解雷诺方程和流量连续方程。对于轴承的承载力、温升和摩擦功耗等参数均给出求解方法,为动静压轴承的设计计算及分析提供一个理论基础,为工程设计计算提供指导作用。     

计入非牛顿效应的曲轴轴承的混合润滑分析

分析了剪切变薄的非牛顿流变学特性和两表面都具有的纵向、横向和各向同性粗糙度对动载有限宽径向滑动轴承性能的综合影响。 Ｃｈｒｉｓｔｅｎｓｅｎ 的粗糙表面流体动力润滑的随机模型和 Ｇｒｅｅｎｗ ｏｏｄ Ｔｒｉｐｐ 接触压力的计算模型用于处理粗糙问题,并考虑了磨合对粗糙高度分布的影响。幂律流体模型用来表征剪切变薄的流变学特征,质量守恒的油膜破裂算法用于雷诺方程的求解。计算结果表明,粗糙度总是减小最小名义油膜厚度,并使油膜压力在接触区剧烈振荡,其幅值大于光滑表面时周期内的最大名义油膜压力。名义最小油膜厚度在纵向粗糙时最大,横向粗糙时最小。粗糙纹理相同时,相同粗糙结构下的名义最小油膜厚度在牛顿流体时大于不同粗糙结构时的相应值,在非牛顿流体情况下,结论相反。混合润滑的轴承性能受粗糙纹理和结构、幂律指数、轴承几何结构、轴颈质量及运行工况的综合影响。     

计处剪切变薄和粘弹效应的数据库辅助曲轴轴承分析

数据库由采用雷诺边界条件和考虑供油特性的影响，联立求解雷诺方程和热平衡方程获得的全油槽、半油槽和单孔轴承的对应于一系列幂律指数、偏心率、偏位角、旋转、挤压和供油压力因子的无量纲油膜承载能力、最大油膜压力、流量和耗功组成。剪切变薄和粘弹效应分别由幂律流体和Ｍａｘｗｅｌｌ流体表征。数据库线性插值。本方法在４８６／６６微机 上运动仅需几分钟，其精度完全满足轴承设计的需要。     

计入剪切变薄和粘弹效应的数据库辅助曲轴轴承分析

数据库由采用雷诺边界条件和考虑供油特性的影响，联立求解雷诺方程和热平衡方程获得的全油槽、半油槽和单孔轴承的对应于一系列幂律指数、偏心率、偏位角、旋转、挤压和供油压力因子的无量纲油膜承载能力、最大油膜压力、流量和耗功组成。剪切变薄和粘弹效应分别由幂律流体和Ｍａｘｗｅｌ流体表征。数据库线性插值。本方法在４８６／６６微机上运行仅需几分钟，其精度完全满足轴承设计的需要。     

工业汽轮机油楔式径向轴承结构及性能分析

介绍了工业汽轮机油楔式径向轴承的结构、性能以及特点.通过对油楔式径向轴承的特性分析以及和可倾瓦轴承的比较,论述了油楔式径向轴承的优越性.总结表明,油楔式径向轴承结构简单、承载力大、运行安全可靠,在工业汽轮机领域,其使用场合远大于可倾瓦轴承.     

功能梯度主轴承的热弹流润滑特性耦合分析

为了对包含功能梯度层的主轴承热弹流润滑耦合特性进行研究,以柴油机主轴承为研究对象,基于格点型有限体积法离散瞬态雷诺方程、热传导方程和热弹性方程,对于离散后的代数方程组采用多重网格法求解,能量方程采用差分法求解,进而得到轴承的油膜润滑特性及轴瓦热弹性结果,通过对比研究发现:功能梯度层可以有效缓解材料分界面附近的应力突变现象;材料指数的增大会使功能梯度层的物性参数变化更均匀,从而使最大油膜压力、最大油膜温度及材料分界面处的应力等出现一定程度的降低.     

悬臂转子系统振动特性分析

推导建立了考虑转轮叶片作用的悬臂转子系统动力学方程.对运动微分方程进行数值积分,分析了质量偏心、转轮叶片质量及轴承之间的距离等对悬臂转子系统振动特性的影响.数值分析结果表明,随着圆盘2质量偏心的不断增加,转子系统的径向位移近似线性增大;当转轮叶片质量、轴承之间的距离等取不同值时,转子系统径向位移的变化情况较为复杂.圆盘1的径向位移值可能会大于、等于或小于圆盘2的径向位移值.     

柴油机主轴承内滑油流动特性分析与试验研究

基于雷诺方程对柴油机主轴承内滑油流动进行了数值分析,得到了主轴承内不同供油压力下滑油的流动特性和压力分布;并利用滑油系统试验台进行主轴承缩比模型试验,以验证数值模拟方法的可靠性。试验表明:数值模拟计算结果与缩比模型试验结果吻合较好;同时也验证了缩比模型试验方案的正确性,为进一步研究柴油机主轴承润滑系统提供了理论和试验基础。     

基于三维有限元波箔片模型的气体箔片轴承承载性能研究

波箔型空气动压轴承在小型高速旋转机械中具有广阔的应用背景,其承载性能受箔片弹性变形影响较大.通过三维有限元法建立箔片变形模型,采用气膜压力分布的二次分布逼近建立箔片弹性变形表达式,实现与气体润滑雷诺方程耦合求解;提出了小柔度步计算方法,以提高箔片轴承大偏心率运行下承载性能求解的稳定性.在验证气体箔片动压轴承求解算法准确性后,分析了波箔片弹性和平箔片厚度对轴承承载力的影响.研究表明:波箔片的波宽是影响气体箔片轴承承载能力的重要参数,而波高在对波箔片刚度影响较小.波箔片刚度和平箔片厚度需合理设计,其有助于提高轴承承载力.     

可倾瓦推力轴承不稳定性研究

和径向可倾瓦轴承类似，蒙受轴向载荷的可倾瓦推力轴承的刚度与阻尼系数强烈地依靠于外界扰动频率。通过对一简单可倾瓦推力轴承轴向动特性系数解析解的讨论表明，由于上述频率的影响，在一定条件下动态油膜力有可能产生轴向负阻尼，这在讨论系统轴向瞬态过程或稳定性问题时是应当引起注意的。     

Influence of thermal pressure and temperature profile approximations in thermohydrodynamic analysis of surface-textured noncircular journal bearing

The present study aims to study the thermohydrodynamic performance of noncircular journal bearings lubricated with multigrade oil. Experimental investigations are carried out on phosphorous bronze hydrodynamic journal bearing with a surface textured at different loading conditions with multigrade oil (MAK 2T oil) as lubricant at different constant rotational speeds (i.e., 1000–4000 rpm) for studying the dynamic characteristics. The journal-bearing's thermodynamic behavior is analyzed by simplifying modified Reynolds and energy equations to obtain surface-textured bearing performance characteristics, such as load-carrying capacity, mass flow rate, and power loss. The noncircular bearings suggest several design parameters, such as a tilt angle for designers. By considering thermal effects for MAK 2T oil lubricant, the requirements of a specific application can be fulfilled.     

A Reynolds analogy for real component surface roughness

A new Reynolds analogy equation is presented, which is based on flow and thermal behavior in a rectangular cross-section channel with real component surface roughness. This roughness is similar to that which exists on some turbine surfaces under extreme operating conditions, or on surfaces of other industrial devices, with deposit accumulation such as heat exchangers. Skin friction coefficient, Nusselt number, Stanton number, and performance factor experimental results are given over a range of Reynolds numbers for one polished smooth surface, and for two other surfaces with different levels of irregularly shaped and irregularly distributed, three-dimensional surface roughness. The Reynolds analogy deduced from these data, with such roughness, is important because it is different from Reynolds analogy equations for surfaces with uniformly shaped elements arranged in a regular, periodic pattern.     

Experimental and numerical studies of liquid flow and heat transfer in microtubes

Experimental and numerical studies were conducted to reveal the flow and heat transfer characteristics of liquid laminar flow in microtubes. Both the smooth fused silica and rough stainless steel microtubes were used with the hydraulic diameters of 50–100 μm and 373–1570 μm, respectively. For the stainless steel tubes, the corresponding surface relative roughness was 2.4%, 1.4%, 0.95%. The experiment was conducted with deionized water at the Reynolds number from 20 to 2400. The experimental data revealed that the friction factor was well predicted with conventional theory for the smooth fused silica tubes. For the rough stainless steel tubes, the friction factor was higher than the prediction of the conventional theory, and increased as the surface relative roughness increased. The results also confirmed that the conventional friction prediction was valid for water flow through microtube with a relative surface roughness less than about 1.5%. The experimental results of local Nusselt number distribution along the axial direction of the stainless steel tubes do not accord with the conventional results when Reynolds number is low and the relative thickness of the tube wall is high. The numerical study reveals that the large ratio of wall thickness over tube diameter in low Reynolds number region causes significant axial heat conduction in the tube wall, leading to a non-linear distribution of the fluid temperature along the axial direction. The axial heat conduction effect is gradually weakened with the increase of Reynolds number and the decrease of the relative tube wall thickness and thus the local Nusselt number approaches the conventional theory prediction.     

Rough annulus pressure drop—interpretation of experiments and recalculation for square ribs

A method is presented which allows the interpretation of pressure drop measurements with rough tubes, annuli and parallel plates. A parameter deduced describes the effect of roughness on a turbulent velocity profile. As a result, experimental data with various roughnesses and channel geometries can be generalized and made comparable. The paper summarizes the results of the interpretation of data with rectangular cross section roughnesses given by numerous authors in the literature.

Finally, examples of the recalculation of friction factors are shown, provided that Reynolds numbers of the flow, channel and roughness geometries are given. The results prove that the method proposed enables us to calculate friction factors of isothermal turbulent flow in concentric annuli with rough inner tubes with a precision which is sufficient for design problems.     

内燃机轴瓦烧损的原因及预防

随着内燃机工业的发展和市场的普及,烧瓦抱轴是内燃机常见故障之一,但轴瓦失效分析是个复杂的系统工程,分析轴瓦失效重在寻找原因,以便“对症下药”,进行纠正和预防。轴瓦的失效往往是由于内燃机在使用中机油变质或短缺,没有合理形成正常的油膜厚度;以及轴颈与轴瓦的装配间隙;还有机油压力低是影响润滑效果的关键指标,使得曲轴与轴瓦之间因缺少机油润滑而“咬死”。并在多年的研究工作中积累了许多方面轴瓦失效的资料,对实物分析多件为例,分别归类:失效形式包括严重拉伤、缺少润滑油,干摩擦产生合金层熔化、和摩擦副的摩滑面没有保持一定厚度的油膜和各种局部过载疲劳破坏、气蚀和V形破坏等。     

Heat transfer coefficient and friction factor correlations for rectangular solar air heater duct having transverse wedge shaped rib roughness on the absorber plate

As is well known, the heat transfer coefficient of a solar air heater duct can be increased by providing artificial roughness on the heated wall (i.e. the absorber plate). Experiments were performed to collect heat transfer and friction data for forced convection flow of air in solar air heater rectangular duct with one broad wall roughened by wedge shaped transverse integral ribs. The experiment encompassed the Reynolds number range from 3000 to 18000; relative roughness height 0.015 to 0.033; the relative roughness pitch 60.17φ^−1.0264<p/e<12.12; and rib wedge angle (φ) of 8, 10, 12 and 15°. The effect of parameters on the heat transfer coefficient and friction factor are compared with the result of smooth duct under similar flow conditions. Statistical correlations for the Nusselt number and friction factor have been developed in terms of geometrical parameters of the roughness elements and the flow Reynolds number.     

增压中冷柴油机主轴承润滑特性研究

基于弹性流体动力润滑理论,建立了4缸柴油机主轴承润滑仿真模型,研究了不同转速下内燃机轴瓦与轴承座的弹性变形、轴瓦与轴颈粗糙度对主轴承润滑特性的影响。研究结果表明:5个主轴承膜厚比均大于1,其中第5主轴承峰值油膜压力与其他4个主轴承相比明显偏大,而且存在偏磨现象,润滑相对恶劣;优化后第5主轴承峰值油膜压力平均降低了20%,最小油膜厚度平均增加了25%,摩擦功耗平均降低了43%。     

Laminar,transitional and turbulent friction factors for gas flows in smooth and rough microtubes

Theoretical and experimental works on microscale transport phenomena have been carried out in the past decade in the attempt to analyze possible new effects and to assess the influence of downscaling on the classical correlations which are used in macro-scale heat and fluid flow, following the need to supply engineers with reliable tools to be used in the design of micro-scale devices. These results were sometimes in mutual contrast, as is the case for the determination of the friction factor, which has been found to be lower, higher or comparable to that for macroscopic channels, depending on the researchers. In this work the compressible flow of nitrogen inside circular microchannels from 26 μm to 508 μm in diameter and with different surface roughness is investigated for the whole range of flow conditions: laminar, transitional and turbulent. Over 5000 experimental data have been collected and analysed. The data confirmed that in the laminar regime the agreement with the conventional theory is very good in terms of friction factors both for rough and smooth microtubes. For the smaller microchannels (<100 μm) when Re is greater than 1300 the friction factor tends to deviate from the Poiseuille law because the flow acceleration due to compressibility effects gains in importance. The transitional regime was found to start no earlier than at values of the Reynolds number around 1800. Both smooth and sudden changes in the flow regime have been found, as reported for conventional tubes. Fully developed turbulent flow was attained with both smooth and rough tubes, and the results for smooth tubes seem to confirm Blasius' relation, while for rough tubes the Colebrook–White correlation is found to be only partially in agreement with the experimental friction factors. In the turbulent regime the dependence of the friction factor on the Reynolds number is less pronounced for microtubes than the prediction of the Colebrook–White correlation and the friction factor depends only on the microtube “relative roughness”.     

Convective nanofluid flow over a vertical cone with a rough surface

In recent literature, the analysis of a combined convective flow over a cone has received a lot of attention. To explore the convection effects of flow over a cone in greater detail, in this investigation, we have considered a cone with a rough surface, which is entirely a new flow problem. Recent studies have shown the influence of roughness on fluid flow over several geometries, but flow over a rough conical surface has not been studied so far. In addition, we have analyzed the effects of nanoparticles, magnetohydrodynamic (MHD), and suction/blowing, which could have significant impacts on characteristics of fluid flow over the cone with a rough surface. Initially, the governing equations, which are partial differential equations with a high degree of nonlinearity, are nondimensionalized through Mangler's transformations. Later, linear equations are obtained via the method of quasilinearization, which is then solved numerically through finite difference approximations. The roughness of the cone's surface has notable effects on fluid flow, that too away from the origin. In fact, the roughness increases the friction at the cone's surface. Furthermore, the magnetic field applied at the wall increases the surface friction. Thus, the combination of roughness and MHD helps delay the boundary layer separation. On the other hand, the suction reduces the temperature of the fluid and increases the energy transport strength, while the thermophoresis parameter exhibits the contrary nature. Therefore, the combined consideration of these two could enhance energy transport strength in several industrial applications.