Simulation and experimental analysis of supporting characteristics of multiple oil pad hydrostatic bearing disk

To study the heavy hydrostatic bearing with multiple oil pads, a reasonably simplified model of the pad is put forward, and the mathematical model of the bearing characteristics of the multiple oil pad hydrostatic bearing is built with consideration of variable viscosity. The pressure field in the clearance oil film of the hydrostatic bearing at various velocities is simulated based on the Finite Volume Method (FVM) by using the software of Computational Fluid Dynamics (CFD). Some pressure experiments on the hydrostatic bearing were carried out and the results verified the rationality of the simplified model of the pad and the validity of the numerical simulation. It is concluded that the viscosity has a great influence on the pressure in the heavy hydrostatic bearing and cannot be neglected, especially, in cases of high rotating speed. The results of numerical calculations provide the internal flow states inside the bearing, which would help the design of the oil cavity structure of the bearing in engineering practice.     

温粘效应下椭圆瓦轴承动特性系数一维模型算法分析

该文建立了轴向解析、周向有限元压力分布的一维变粘度场有限宽椭圆瓦轴承动特性系数模型.忽略泊肃叶流项对速度的影响,不考虑轴向温度变化并沿径向方向积分,三维能量方程可降阶为平均温度场只沿周向分布的一维形式,与雷诺方程解耦.采用一维直接解法求解雷诺方程和轴承在平衡点的挠动和速度方程.既考虑了温粘效应对轴承动力学性能的影响,又提供了无需迭代确定油膜破裂边界和求解油膜力和动特性系数快速算法.作为应用,对进油槽位于水平两侧的椭圆瓦轴承进行了动力润滑热效应分析,与工程数据比较,计算结果稳合,证明该模型合理,适用于工程上多瓦轴承的分析计算.     

高海拔地区气压环境对高速水流空化特性的影响

为定量评价高海拔地区的低气压环境对水流空化特性的影响程度,通过理论计算单气核临界压强在不同气压条件下的变化,分析单气核临界压强变化对初生空化数的影响程度,并进行不同海拔高程下水流空化数的敏感性分析。研究成果表明:低气压环境下,气核初生空化数和水流空化数均减小,但水流空化数减小的程度远远大于初生空化数减小的程度,其他条件相同的前提下,高海拔地区的高速水流空化空蚀风险增大。研究结论可为高海拔地区高速水流的空化空蚀设计和评价提供参考。     

THE EFFECT OF OIL CAVITY DEPTH ON TEMPERATURE FIELD IN HEAVY HYDROSTATIC THRUST BEARING

For a heavy hydrostatic bearing with a high linear velocity,the results of numerical calculations often differ from practical conditions if the viscosity is considered as constant.In this article,the influence of the oil cavity depth on the temperature field in the heavy hydrostatic bearing is discussed in the context of variable viscosity.The viscosity-temperature relations for the gap oil film are first established by fitting B-Spline curves,then,numerical calculations for the temperature field in the heavy hydrostatic bearing of different oil cavity depths are carried out based on Finite Volume Method (FVM) under the same rotating speed,and the influence of the oil cavity depth on the temperature distribution in the gap oil film of the hydrostatic bearing is discussed.The results of numerical calculations provide the temperature distribution state inside the hydrostatic bearing,which would help the selection and the design of hydrostatic bearings in engineering practice.     

Shedding frequency of sheet cavitation around axisymmetric body at small angles of attack

Cavity shedding of cavitating flows around an axisymmetric body belongs to the unsteady cavitating flows in the condition of steady incoming current.The periodic characteristics of unsteady cavitating flows around an axisymmetric body at small angles of attack are investigated experimentally and numerically.The evolution and shedding process of the three-dimensional sheet cavitation are computed numerically by the Reynolds averaged Navier-Stokes equations and the RNG k-?model.The modification approach for eddy viscosity coefficient in the transition area of the two-phase flow is adopted to reproduce the shedding process of cavitating flows.The computed frequency of the cavity shedding coincides with the experimental data for the cases of unsteady cavitating flows around axisymmetric bodies with four headforms.Given the cavitation number,the shedding process of the cavitating flow depends heavily on the headform of the axisymmetric body.If the angle of attack of the axisymmetric body is greater than a critical value,the violent shedding of the sheet cavitation seems to be depressed.     

HYDRODYNAMIC AND ELASTOHYDRODYNAMIC STUDIES OF A CYLINDRICAL JOURNAL BEARING

In this article, the effect of the bearing elastic deformation on the performance characteristics of a cylindrical journal bearing is analyzed. The variety of simulation models covers hydrodynamic (HD) and elastohydrodynamic (EHD) lubrication theories. The Reynolds equations governing the flow in the clearance space of the journal bearing are obtained by considering the effect of mass transfer across the fluid film. The finite element method with an iteration scheme was employed to solve both the Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell. The converged solutions for the lubricant flow and elastic deformation vector are obtained. Dynamic characteristics of the journal bearing are computed for HD and EHD theories. Numerical simulation results show that the flexibility of bearing liner has a significant influence on the performance of a cylindrical journal bearing. Indeed, the elastic deformations of the bearing liner extend the pressure area in the bearing and increase the minimum film thickness. Although, dynamic coefficient, load capacity and attitude angle decrease.     

OPERATOR-SPLITTING METHOD FOR ANALYSIS OF CAVITATION IN LIQUID-LUBRICATED HERRINGBONE GROOVED JOURNAL BEARING

ＮＯＭＥＮＣＬＡＴＵＲＥｃ　ｒａｄｉａｌｃｌｅａｒａｎｃｅｈ　ｆｉｌｍｔｈｉｃｋｎｅｓｓ ｈ　ｄｉｍｅｎｓｉｏｎｌｅｓｓｆｉｌｍｔｈｉｃｋｎｅｓｓ (ｈ/ｃ)Ｌ/Ｄ　ｒａｔｉｏｏｆｌｅｎｇｔｈｔｏｄｉａｍｅｔｅｒｐ　ｆｉｌｍ ｐｒｅｓｓｕｒｅｅ　ｅｃｃｅｎｔｒｉ     

ACOUSTIC ANALYSIS OF HYDRODYNAMIC AND ELASTO-HYDRODYNAMIC OIL LUBRICATED JOURNAL BEARINGS

The purpose of the present paper is to investigate the effect of elastic deformation of bearing liner on the acoustic behavior of oil lubricated journal bearings.Analysis is performed for hydrodynamic(HD) and elasto-hydrodynamic (EHD) lubrications.Dynamic behavior and acoustical properties are investigated through an analysis of pressure fluctuation calculated from the Reynolds equation governing the flow in the clearance space of the journal bearing.This is solved numerically using the finite difference method with the successive over relaxation technique.In elasto-hydrodynamic lubrication,the finite element method with in iteration scheme is adopted to solve both Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell.The results show that the sound pressure level of the bearing is markedly influenced by the flexibility of the bearing liner,the viscosity of lubricant and the load applied to journal.HD analysis shows that the journal centre’s orbit,from a disturbed position,converges to the static equilibrium position faster than EHD lubrication.The results of the present paper could aid in the design of low-noise rotor-bearing systems supported by oil lubricated journal bearings.     

Cavitation erosion in bloods

The cavitation in a mechanical heart valve(MHV) is a serious concern. In most of the investigations of the MHV cavitation in vitro, the tap water, the distilled water, or the glycerin are used as the test liquids, instead of the real blood. Therefore, the effects of the liquid properties on the cavitation can not be well revealed. In this paper, the cavitation erosion in the porcine bloods is experimentally investigated as well as in the tap water and the distilled water by means of a vibratory apparatus. The results show that the blood produces a weaker intensity of the cavitation erosion than the tap water or the distilled water. The cavitation erosion decreases with the decrease of the liquid temperature or with the increase of the concentration of the blood, especially with the increase of the liquid viscosity. It is the viscosity that could be a major dominant factor affecting this erosion. The temperature or the concentration of the blood changes the viscosity, and in turns changes the intensity of the cavitation erosion.     

EXPERIMENTAL STUDY OF EFFECTS OF AIR CONTENT ON CAVITATION AND PRESSURE FLUCTUATIONS

This article studies the effects of air content on propeller cavitation and pressure fluctuations. The cavitation is observed while the pressure fluctuations on the hull are measured. When adjusting the air content, the sheet cavitation range does not change distinctly, but the pressure fluctuations see obvious differences. The amplitudes of the pressure fluctuations increase with the decrease of the air content. The results indicate that the air content has little effect on the sheet cavitation range but has an important effect on the bubble cavitation and the tip vortex cavitation. When the air content decreases, the water tensile force increases, which results in the instability of the bubble cavitation and the tip vortex cavitation and the increase of the pressure fluctuations. To minimize the scale effects, the experiments should be run at a high Reynolds number with a high nuclei content. The high Reynolds number is often realized by increasing the flow velocity and the propeller rotation speed, and the high nuclei content is often made by increasing the dissolved air content.     

15度斜式轴流泵装置水动力特性实验研究

15度斜式轴流泵装置是我国近年在低扬程、大流量泵站引入的一种新型泵装置,由于出水流道前端呈S形弯曲,流道内的二次流导致某些工况下压力脉动和振动较大,这一问题尚有待深入研究。本文针对浙江盐官泵站技术改造所研制的新型15度斜式轴流泵装置进行了水动力学特性的实验研究。研究发现,与泵段相比,斜式轴流泵装置的最优工况点向负叶片角度和小流量区偏移。泵装置在较小叶片角度下的空化特性优于大叶片角度;当装置空化余量低到使泵装置效率下降1%时,叶片背面出现占据近1/3叶道区域的空化区。斜式轴流泵的飞逸转速在较大负叶片角度时可达额定转速的1.73倍。斜式轴流泵压力脉动在导叶出口、出水弯管和出水流道内明显高于常规立式轴流泵;从水泵进口方向看,当叶轮逆时针方向旋转时,斜式轴流泵装置出水流道隔墩左侧流量大于右侧。本文研究成果为大型斜式轴流泵站优化设计和稳定运行提供了新的科学依据。     

Occurrence of hydrodynamic cavitation

In this paper, the conditions under which cavitation (or liquid film rupture) can or cannot occur in thin layers of moving liquid are derived for three typical cases. At the same time, expressions depending on geometrical and movement parameters, where cavitation might start, are given. The results are obtained using simple engineering terms, which can be used in cases whether it is necessary to avoid cavitation or to induce it.     

基于在线数据的抽水蓄能机组推力油膜综合厚度研究

随着我国建设的抽水蓄能电站不断增加,且抽水蓄能机组经常面临工况的急剧转换,从机械设计上抽水蓄能电机的推力轴承采用中心支撑和双向高速运行,因此推力轴承部件成为抽水蓄能机组运行过程中重点监测对象,如何对其进行安全监控与管理就变得尤为重要。推力轴承处频繁出现的故障现象就是推力瓦存在着刮瓦现象,这种现象如果恶化就会导致推力瓦烧瓦事故,造成这种现象的原因很可能是机组在低速旋转时,由于推力油膜形成条件变差所致。为了更好地实现对推力轴承油膜厚度的实时监测,消除电站运行安全隐患,充分发挥其经济效益,本文提出一种基于在线数据的抽水蓄能机组推力油膜综合厚度研究,并利用抽水蓄能电站的推力轴承状态监测实际运行数据,对其进行系统分析,为抽水蓄能电站优化运行的监控和管理提供了重要的参考依据,保障机组的安全平稳运行。     

CAVITATING SUPPRESSION OF LOW SPECIFIC SPEED CENTRIFUGAL PUMP WITH GAP DRAINAGE BLADES

This paper aims to clarify the cavitation suppression mechanism of the gap structure impeller based on the analysis of cavitation characteristics in a low specific speed centrifugal pump. In order to obtain reliable and consistent numerical results, some numerical considerations and modeling methodology were demonstrated and researched, and a check of the time and space resolution were also conducted. Hence the predicted cavitation performance of the two centrifugal pumps were investigated and compared with experimental results, and they were in qualitative agreement. It was confirmed that the new gap structure impeller has a very good characteristic of inhibiting cavitation, especially in large flow area, the present numerical method can effectively capture the major internal flow features in the centrifugal pump, through the comparison of the two type impeller flow fields, the cavitation suppression mechanism of the gap impeller may be the combination effects of the small vice blade’s guiding flow and gap tunnel’s auto-balancing of pressure.     

高水头深孔平板门门槽水力特性研究

平板闸门门槽内的水流流态十分复杂,容易因空化空蚀而破坏门槽。以卡基娃水电站放空洞工程为实例,采用水工模型试验探讨门槽附近水流流态、压力、空化数的变化规律。研究结果表明:有压式门后连接段能较好地改善门槽及门后连接段水流的流态;闸门全开时,各个区域没有负压出现,水流发生空化的可能性也较低;闸门局开时,门槽及门后连接段会出现负压,最大负压出现在门槽的底板处,水流发生空化的可能性也较大;水流的脉动表现出明显振幅大、频率低的强紊流脉动压力的特点。研究成果对于高水头深孔闸门门槽的设计具有一定的借鉴意义。     

葛洲坝电厂水轮发电机组技术改造简述

葛注坝水电厂水轮发电机组存在着推力瓦烧损，大轴密封发卡，控制环抗磨块脱落，剪断锁易剪断等问题。针对其产生的原因采取了一些改进措施和进行了改造，收到了很好的效果。调速器更换为SJ－721A型电调DTJ－150／4－E1机械柜和WBST－A微机步进电机式调速器等，其主要技术性能达到国际先进水平。170MW机组的环形接力器由于刚度小变形大活塞漏油严重，改造中用4个摇摆接力器替代，确保了机组的稳定运行。水轮机叶片外缘加裙边后不仅振动减小，间隙空蚀减轻，在某些工况效率还有所提高。推力轴瓦更换为弹性金属塑料瓦，其承载能力大，摩擦系数小，安装工艺简单，改造是成功的，但仍存在着烧瓦的隐患。水轮机喷涂抗磨保护层收到一些效果，但中环和叶片强空蚀区的磨蚀尚无有效的解决办法。     

高速潜水轴流泵大流量工况的空化特性

为了研究大流量工况下高速潜水轴流泵的空化特性,基于ANSYS CFX软件,选取Zwart、Kunz以及Schnerr-Sauer 3种空化模型进行大流量工况下高速潜水轴流泵外特性和泵内空化流动特性数值模拟。结果表明:大流量工况下Schnerr-Sauer空化模型预测的外特性变化趋势与试验值最为吻合,相较于另两种空化模型,Schnerr-Sauer空化模型模拟的叶片背面空泡体积分数较高;空化严重区域主要出现在叶片背面进口附近以及叶顶,同一空化数下,流量越大,叶片空化状况越严重;叶片载荷分布由叶片进口边到出口边呈先增大后减小的趋势;各流量下空泡首先出现在叶片背面进口前缘位置,随着空化数的减小,空泡体积分数沿着主流方向朝叶片后缘不断增大直至空泡占据整个叶片背面;叶片背面处的三角形云状空化尾缘空穴极不稳定,随着叶轮旋转,尾缘处空泡微团逐渐脱落,朝着相邻叶片不断移动,对相邻叶片的工作面产生侵蚀破坏,导致叶片载荷发生变化,对轴流泵水力性能产生影响。     

VIBRATION OF A SINGLE PROTEIN BUBBLE IN BINGHAM LIQUID

The vibration of a single protein bubble may take place under the action of high pressure difference. In this process, the bubble wall may experience a finite deformation. The equation describing the dynamics of the protein bubble with viscoelastic film in Bingham liquid is derived. A numerical solution to this equation is carried out to study the effect of liquid pressure, the characteristic parameters of Bingham liquid and the viscosity of the protein film on the finite deformation of the bubble. The results show that the vibration of the protein bubble wall is caused by the action of pressure difference, the elastic stress in finite deformation and the dissipation of viscosity of the protein film and Bingham liquid. The vibration is nonlinear. Decreasing the pressure difference between gas and Bingham liquid on both sides of the protein bubble will lead to a change of vibration performance. The frequency and amplitude are reduced, tegether with the speed of vibration damping. In addition, the deformation rate of the bubble is smaller when the amplitude of vibration is reduced, which means shorter time to reach a balance state. On the other side, the increase of the magnitude of viscosity of the protein film or the plastic viscosity of Bingham liquid can restrain the vibration of the protein bubble wall in the course of finite deformation, as a result, the load bearing capacity of bubble is enhanced.     

水轮发电机推力轴承在线振动监测系统设计与应用

传统推力轴承运行参数的监测对象局限于油温、瓦温、油膜压力和油膜厚度等,无法得到镜板波浪度、推力瓦不水平度、推力瓦不水平方位、镜板与大轴的不垂直度、镜板与大轴的不垂直方位等重要参数。针对上述问题,提出了一种新型的推力轴承在线振动监测系统。在详细阐述系统体系的基础上,给出了数据处理的关键技术,获得了表现推力轴承状态的量化结果。该系统具有通用性强、精度高的特点,有较好的应用和推广价值。     

The development of a lubricant traction measurement system

A ball-disc traction test rig is improved through the development of a lubricant traction measurement system, consisting of a resonance force sensitive quartz sensor, a circuit of the sensor and a rigid bracket jointed by a frictionless hinge.The traction coefficients of a kind of domestic lubricating oil were measured at various normal loads, rolling velocities, lubricant inlet temperatures and slide-to-roll ratios on a ball-disc traction test rig equipped with this traction measurement system.The results show that the traction test curve is smooth and the data enjoy a good accuracy, which indicates that the design of the lubricant traction measurement system is reasonable and the precision of the system is high, especially, at high temperature, high rolling speed and small slide-to-roll ratio.