Squeeze fluid film of spherical hydrophobic surfaces with wall slip

Isothermal squeeze film flow of Newtonian fluid between spherical hydrophobic surfaces with wall slip is investigated using a limiting shear stress model and complementary algorithm. Wall slip velocity is controlled by the liquid–solid interface limiting shear stress. It is found that the wall slip dramatically decreases the hydrodynamic support force of the squeeze fluid film. In the case of large wall slip the hydrodynamic support force increases only slightly with the decrease in the film thickness. We find that wall slip decreases with increasing film thickness and limiting shear stress, but increases with increasing fluid viscosity and approaching velocity. An empirical equation is given for prediction of the fluid load support capacity. The possible effect of pressure on wall slip is also discussed. It is found that fluid pressure suppresses wall slip after the proportionality coefficient of limiting shear stress reaches a critical threshold. However, almost no effect is found when it is below this critical threshold. Good agreements exist between the present theoretical predictions and some existing experimental observations.     

Abnormal behavior of a hydrodynamic lubrication journal bearing caused by wall slip

Reynolds lubrication theory assumes that there is no wall slip on the interfaces between the solids and lubricant. During recent years, however, it is found that wall slip often happens. The present paper analyzes the wall slip occurring in a hydrodynamic lubrication journal bearing. If the two surfaces have the same adhesion property wall slip always decreases the oil film load support capacity. If there is wall slip over all of the lubricated surfaces, the hydrodynamic effect of the journal bearing vanishes, and no load support exists. If the two lubricated surfaces have different adhesion properties, the wall slip effect is more complex and may cause the journal bearing to operate in an instable manner. In order to avoid the wall slip, the limiting shear stress at the bearing surface should be higher than that at the journal surface.     

Numerical investigation of the combined effects of slip and texture on tribological performance of bearing

Slider bearings are used in many applications. An increase in the load support may allow for saving of energy. In this work, in order to enhance the load support and decrease the friction force, a combined textured surface bearing using boundary slip is discussed. A modified Reynolds equation with slip is adopted. With the main goal of evaluating the effects of slip and texture, a parametric analysis is performed. For the given operating conditions, texturing features as well as slip pattern are analysed in detail. The numerical analysis is undertaken under the condition of different gap ratio values and the slip-textured area. The results show that combined techniques of slip and texture have a significant effect on the improvement of the tribological performance of bearing, that is, a high load support but low friction force. The gap ratio of the bearing is shown to have a significant effect on the lubrication behaviour. It is found that even with a smallest gap ratio (parallel gap), a high load support can be produced. However, it is also shown that the gap ratio appears to contribute to the generated friction force and the volume flow rate more than the boundary slip. Further analysis indicates that the optimum slip-text zones for certain gap ratio are highlighted. These findings may provide references for designing hydrodynamic-textured slider bearing considering boundary slip.     

水滴迷宫式调节阀空化特性计算与结构改进

针对超(超)临界机组中水滴迷宫式调节阀在高温高压工况下引起的严重气蚀问题,基于计算流体力学理论和空化机理,选用标准k-ε湍流模型、Mixture模型和Schnerr-Sauer空化模型,比较了改进前后调节阀在典型开度下的压力、速度、气相体积分数等结构性能.计算结果表明:原始碟片结构压降大,最大可至19.95 MPa,流...     

基于Fluent的螺旋槽干气密封数值模拟与分析

笔者从计算流体力学出发,使用GAMBIT对模型进行网格划分,用世界著名的CFD软件Fluent对螺旋槽干气密封进行了数值模拟分析,并与权威的试验值进行比较,验证了所用方法在螺旋槽干气密封研究中应用的可行性和可信性。     

基于热机耦合的机体主轴承壁性能数值模拟与实验研究

针对一款2.7 L高增压柴油机,采用有限元方法计算了机体的结构强度,分析了热载荷与机械载荷对机体主轴承壁区域的应变分布影响。设计了发动机台架实验,测取机体主轴承壁面的温度与动态应变,对计算结果进行验证并分析了产生误差的原因。研究结果表明:机体主轴承壁的工作应力由热应力与动载应力两部分组成,在额定工况下,热应力占主导地位。通过对比模拟与实验结果可以发现,基于第3类热载荷边界条件计算得到的壁面温度精度较高,但是该方法精度强烈依赖输入的换热系数精度。基于有限元方法获得的应变模拟值表现出良好的跟随性。有限元方法对最大动载荷模拟精度较高。最大工作应变计算误差主要来自于最大热应力的计算误差。计算模型的拓扑网格结构、测点当地材料属性与换热条件是造成计算误差的3个主要因素。     

超长筒段内壁螺旋焊缝跟踪打磨控制研究

针对超长筒段内壁螺旋焊缝的打磨需求,设计了一种高精度内壁螺旋线焊缝打磨控制方法,通过速度反馈匹配、视觉图像补偿等多重手段,建立了实时跟踪检测机制,解决了螺旋线焊缝跟踪不同步的问题,实现了焊缝的精确打磨加工。通过实验验证了此控制方法的可行性,采用西门子的控制系统、伺服驱动器、编码器和视觉图像系统,结合机械结构系统,包括滚轮架、柔顺打磨工具、电机及行走轨道等,搭建全闭环软硬件控制系统平台,经过调试验证,通过图像系统实时监控和实际打磨效果的结合,验证了此方法应用于内壁螺旋线打磨的有效性,实现了精确跟踪打磨。     

高温高流速环烷酸冲刷腐蚀流场数值模拟研究

采用CFD技术对高温高流速环烷酸喷射试验装置的流场进行数值模拟,主要分析了喷嘴至壁面距离H、喷嘴出口流速U和流体温度T的变化对喷嘴外部区域流场分布情况的影响。结果表明:随着U的增大,H和T的减小,壁面剪切应力逐渐增大;近壁处湍流强度随U的增大和H的减小而增强;减小H能增强喷射流体冲刷效果,但是H过小时,喷嘴出口压力过大,影响设备安全运行。为了提高试样壁面冲刷腐蚀效果,达到加速试验和安全运行目的,建议H取4～8 mm为宜。     

滚动轴承寿命计算方法发展的研究与分析

详细介绍了滚动轴承疲劳寿命的概念,并对滚动轴承疲劳寿命的发展历程进行了详细阐述,分析了各个不同时期寿命计算理论的特点,谨供相关人士参考。     

Numerical analysis of journal bearings lubricated with micropolar fluids including thermal and cavitating effects

A numerical study of the non-Newtonian behavior for a finite journal bearing lubricated with micropolar fluids is undertaken considering both thermal and cavitating effects. The modified Reynolds equation and energy equation are derived based on Eringen's micropolar fluid theory. The solution to the modified Reynolds equation is determined using the Elord's cavitation algorithm. The effects of the size of material characteristic length and the coupling number on the thermohydrodynamic performance of a journal bearing are investigated. It is shown, compared with Newtonian fluids, that micropolar fluids exhibit the increase in load capacity and temperature, but the decrease in coefficient of friction and side leakage flow. It is also indicated that, in the full film region, micropolar fluids increase the values of non-dimensional density, while in the cavitated region, both micropolar fluids and Newtonian fluids yield the same values of the fractional film content.     

重油催化主风机组汽轮机振动原因分析及解决措施

某炼油厂检修中发现重油催化裂化装置主风机组中汽轮机轴瓦异常振动,从轴承的承载能力及流 体动力学方面予以分析,故障诊断为转子油膜失稳造成的油膜涡动和机组对中不良所引起的.最后通过提高轴瓦的承载能力,堵塞轴瓦上多余小孔,消除机组对中误差等措施,成功解决了汽轮机轴瓦异常振动故障,确保了机组平稳运行.     

Effects of solid particulate mean diameter on hydrodynamic cavitation intensity and the variation laws and mechanisms in nozzle flows: Numerical simulations and theoretical analysis

Solid particulate and water hydrodynamic cavitation flow (SPW-HCF), one solid-liquid-vapor with phase change three-phase flow, often appears in many different engineering fields. SPW-HCF has both desirable and problematic effects. Solid particulate mean diameter has significant effects on hydrodynamic cavitation intensity. In this study, one new coupled numerical method of vapor, liquid, and solid was built. SPW-HCF with the mean diameter increasing from 0.0015 mm to 0.070 mm in a nozzle was numerically simulated. Effects of solid particulate mean diameter on hydrodynamic cavitation intensity were evaluated. Vapor contents of SPW-HCF and pure water hydrodynamic cavitation flow (PW-HCF) were compared to build the laws and variations of slip velocity, turbulent kinetic energy, and Saffman lift force were analyzed to reveal the mechanisms. The results indicated that for the laws, all SPW-HCF vapor contents were greater than those in PW-HCF. Solid particulates promoted cavitation evolution. The concentration promotion scope decreased as mean diameter increased. For the mechanisms, maximal and absolute minimal slip velocities were higher in SPW-HCF than those in PW-HCF. Moreover, maximal and minimal turbulent kinetic energies of SPW-HCF were higher than those in PW-HCF. Corresponding mixture kinetic energies were higher than those in PW-HCF. With the synergetic effects of slip velocity and turbulent kinetic energy, pressure had significant decrease to promote SPW-HCF development. They were primary factors. The magnitude of Saffman lift force calculated in SPW-HCF was relatively small. The effects on the decrease of pressure were minute. SPW-HCF evolution was affected weakly by this force. It can be considered as a secondary influence factor. The investigation results could provide the references to solve corresponding practical engineering problems.     

基于 Kramers-Kronig 变换的油纸绝缘低频 介电谱分析与建模研究

油纸绝缘低频响应对绝缘状态受潮及老化的诊断至关重要。针对目前关于低频响应数据的分析方法较为缺乏、对应的等效电路模型还不完善的问题,利用Kramers-Kronig变换对油纸绝缘频域介电谱中的电导、无穷频率电容和弛豫过程进行分离;引入基于多体理论的Dissado-Hill模型对低频弛豫过程进行拟合,并构建一种新的油纸绝缘低频响应等效电路模型。最后,对不同含水率油纸绝缘样品的低频响应数据进行建模和参数分析。实验结果表明,利用Kramers-Kronig变换能有效的对油纸绝缘的弛豫过程、电导过程以及无穷频率电容进行解耦;不同含水率样品低频响应模型重构谱线相对于测量谱线的拟合优度在0.98以上,验证了模型的准确性;低频弥散极化率幅值χ_(LFD)(0)与微水含量之间存在指数函数关系,其拟合优度高达0.99,可作为油纸绝缘微水含量定量评估的新特征量,为油纸绝缘受潮状态诊断提供新思路。     

超高速离心叶轮中固体颗粒运动轨迹的数值模拟与分析

为解决和预测固体颗粒对超高速离心叶轮的冲击磨损问题,以多相流理论为基础,采用了雷诺应力模型结合颗粒轨道模型的方法,通过对超高速离心叶轮内气固两相湍流场的计算,得到了颗粒在叶轮中的运动轨迹;并用CFX对不同粒径的固体颗粒在超高速离心叶轮内部流场中的运动轨迹进行了数值模拟。模拟结果与已有实验结果吻合,说明采用雷诺应力湍流模型能准确描述超高速离心叶轮中固体颗粒的运动轨迹。     

Numerical analysis of installation effects in Coriolis flowmeters: Single and twin tube configurations

A fully coupled, partitioned, numerical model that accounts for fluid–structure interaction is applied for a study of the installation effects of Coriolis flowmeters. The modeled configurations include a single straight-tube full-bore flowmeter and two different twin tube flowmeters with straight and U-shaped measuring tubes. Three different flow disturbance elements positioned upstream of the flowmeter are considered in the study, as well as two different types of flow splitters in the case of the twin tube configurations. The installation effects are estimated by comparing the mass-flow sensitivities under the disturbed and fully developed flow conditions at the inlet of the flowmeter. For the modeled twin tube flowmeters they are found to be of the order of one-tenth of a per cent. These relatively small values of the installation effects are related to the presence of flow splitters and to the averaging of the motion of both measuring tubes in the twin tube configurations. Similarly, averaging the response from two sensor pairs instead of only a single sensor pair reduces the circumferential variations and the peak values of the installation effects for asymmetric flows in the single straight-tube flowmeter.