Film Pressure Distribution Research Articles

Numerical Analyses of Hydrodynamic Lubrication and Dynamics of the Rolling Piston and Crankshaft in a Rotary Compressor

In this article, numerical analyses of hydrodynamic lubrication and dynamics of the crank, rolling piston, and vane were carried out to study the tribological performance of a rotary compressor. Dimensionless Reynolds equations of journal and thrust bearings in dynamic load condition were derived and solved numerically. To deal with the lubrication of the rolling piston, the effect of the nonuniformity of tangential velocity over the bearing surface on the Reynolds equation was taken into account. In addition, combined with the analyses of dynamics and kinematics of the crank, piston, and vane, the angular velocities of the crank and piston as well as the motion mode between the piston and vane were studied. Analysis results illustrate characteristic oil film pressure distributions of the crank and piston bearings, which are different from that of common journal bearings. Under the influences of dynamic load and eccentricity of the cam, the wedge effect as well as the stretch and squeeze effect contribute greatly to hydrodynamic pressure. The relative motion mode between the piston and vane tip is not always pure sliding but accompanies rolling in some cases, which depends on the magnitude of the friction coefficient between the piston and vane tip. The analysis results are helpful for the improvement of rotary compressor design.

Occurrence of High Pressure Spike in Unidirectional Start–Stop–Start Point Contacts

The transient film thickness and pressure distributions in point elastohydrodynamic lubrication (EHL) contacts during start–stop–start motion are discussed based on experimental and numerical analyses. When the machine element starts to move after the stopping, where the oil is entrapped between two surfaces, the pressure at the exit area increases very much. The pressure increase depends markedly on the overall film thickness before the stopping of the motion, but is hardly controlled by the acceleration after the stopping. It can be considered that this phenomenon affects the rolling contact fatigue damage.

Three-Dimensional CFD Simulation for Water-Lubricated Guide Bearing of Large Tubular Pump

A numerical simulation for flow field in water-lubricated guide bearing of large tubular pump is conducted by software Fluent, which shows the pressure distribution of water film with different rotating speeds and the rule of the influence of relevant parameters on the amount of lubricating water, dynamic and static characteristics of guide bearing.The result shows that the pressure distributions of water film at low and high speeds are very different, and with the obvious dynamic pressure effect, the bearing inner can be in a state of reflux and the water-lubricated amount and clearance are reduced. The load capacity and stiffness of guide bearing are increased along with the speed and water pressure increase meanwhile the amount of water is increased along with the speed lowering and the water pressure and clearance increase.

Elastic Deformation Effects on the Thermo-Hydrodynamic Aspect of Porous Journal Bearings

In this paper, the effects of porous bush elastic deformation on the static characteristics of finite porous journal bearing are investigated using Darcy’s law. The modified Reynolds equation applied to thermo-hydrodynamic problems is modified by considering the viscosity variation along the film thickness. The film pressure distribution and other characteristics such as the load carrying capacity and attitude angle are obtained by solving the governing equations numerically. Obtained results showed that deformation is considerable in the maximum pressure zone, and the elastic deformation will decrease the load carrying capacity. The viscosity variation parameter tends also to decrease the load carrying capacity.

Effect of Surface Roughness on the Squeeze Film Lubrication of Finite Poroelastic Partial Journal Bearings with Couple Stress Fluids: A Special Reference to Hip Joint Lubrication

A simplified mathematical model has been developed for understanding the combined effects of surface roughness and couple stresses on the squeeze film behavior of poroelastic bearings in general and that of hip joints in particular. The cartilage is modeled as biphasic poroelastic matrix and synovial fluid is modeled as couple stress fluid. The modified form of averaged Reynolds equation which incorporates the randomized roughness structure as well as elastic nature of articular cartilage with couple stress fluid as lubricant is derived. For the study of rough surfaces, Christensen's stochastic theory is used to study the effect of two types of one-dimensional random roughness, namely, longitudinal roughness pattern and the transverse roughness pattern. The averaged film pressure distribution equations are solved numerically by using the conjugate gradient method. It is observed that the surface roughness effect is dominant and pattern dependent and the influence of couple stresses is to improve the joint performance.

The Numerical Analysis of the Velocity and Pressure Distribution of the Oil Film in Heavy Hydrostatic Thrust Bearing

To study the velocity and pressure distribution of the oil film in a heavy hydrostatic thrust bearing, a mathematical model of the velocity is proposed and the finite volume method (FVM) has been used to simulate the flow field under different working conditions. Some pressure experiments were carried out and the results verified the correctness of the simulation. It is concluded that the pressure distribution varies small under different rotation speed when the surface load on the workbench is constant. But the velocity of the oil film is influenced greatly by the rotation speed. When the rotation speed of the workbench is as quick as enough, the velocity of the oil film on one radial side of the pad will be zero, that is to say the lubrication oil will be drained from the other three sides of the recess.

Numerical analysis of plain journal bearing under hydrodynamic lubrication by water

The article aims to provide references for designing water-lubricated plain journal bearings. Considering the differences between the physical properties of the water and of the oil, the effects of eccentricity ratio on pressure distribution of water film are analyzed by computational fluid dynamics (CFD). Then numerical analysis of journal bearings with different dimensions is undertaken under different rotational speeds. Based on the analysis, a reference is produced for selecting the initial diameter dimension which is used to design an efficient water-lubricated plain bearing under the given load and rotational speed. At last, the reference is verified by an experimental case.

Dynamic Mesh Method for Calculating Bearing Capacity and Overturning Moment of Partial Loaded Hydrostatic Rotary Tables under Rotating Condition

The hydrostatic rotary table's upper and lower guides are prone to scratch each other when the partial loaded hydrostatic rotary table is rotating. In the former study of this phenomenon, it is hard to establish a practical mathematical model of carrying capacity and overturning moment of the hydrostatic rotary table based on traditional analytical calculating method, and the modeling and calculating of fluid domain with a changing geometrical boundary can not be conducted when utilizing the traditional CFD simulation method. To solve this problem, a new calculation method based on dynamic mesh model is proposed, which is used to calculate the bearing capacity and overturning moment of the partial loaded hydrostatic rotary table under rotating condition in engineering practice. The change of oil film form is controlled by using user definition function. Deformation of oil film mesh caused by the changing of rotary table's tilting direction is refreshed using spring smoothing theoretical model. The oil film's moving boundary caused by rotational movement is changed into static boundary for avoiding the grid distortion. This method can realize the simulation of oil film with different thickness and tilt displacement rate using the same model, which can avoid the repeatedly building of calculating model and improving the computational efficiency. The dynamic process of three dimensional pressure distribution of oil film is reappeared. The impact of rotary table's motion on flow field distribution can be reflected in the calculating result which is closer to engineering practice. The bearing capacity and overturning moment of a typical hydrostatic rotary table are calculated by using the proposed method and the experiment of hydrostatic rotary table bearing partial load is conducted. The experimental results are in reasonable agreement with calculation ones, which have verified the effectiveness of the proposed calculating method.

Elastohydrodynamic Lubrication of Inhomogeneous Materials Using the Equivalent Inclusion Method

Solid materials forming the boundaries of a lubrication interface may be elastoplastic, heat treated, coated with multilayers, or functionally graded. They may also be composites reinforced by particles or have impurities and defects. Presented in this paper is a model for elastohydrodynamic lubrication interfaces formed with these realistic materials. This model considers the surface deformation and subsurface stresses influenced by material inhomogeneities, where the inhomogeneities are replaced by inclusions with properly determined eigenstrains by means of the equivalent inclusion method. The surface displacement or deformation caused by inhomogeneities is introduced to the film thickness equation. The stresses are the sum of those caused by the fluid pressure and the eigenstrains. The lubrication of a material with a single inhomogeneity, multiple inhomogeneities, and functionally graded coatings are analyzed to reveal the influence of inhomogeneities on film thickness, pressure distribution, and subsurface stresses.

Experimental investigation of film pressure distribution in water-lubricated rubber journal bearings

Measurements of lubricant film pressure were made on water-lubricated rubber journal bearings with eight axial grooves. For measuring full circumferential pressure of bearing, pressure transducers were mounted on the shaft of test rig. Pressure data were transferred by means of wireless data transmission while shaft rotating. Pressures under different axial positions of bearing were simultaneously measured by different transducers on shaft. Film pressures of bearing operated under different loads, shaft speeds and water supply pressures were compared and analyzed. Experimental results reveal the existence of negative pressure region in water-lubricated rubber bearing. The maximum negative pressure appears at the beginning of the divergent region of fluid film. Different operating conditions are indicated by the fluctuation range of film pressure. For every operating condition, the biggest pressure fluctuation occurs at the axial middle part of bearing. The changes of load and shaft speed have larger influence to film pressure amplitude than the change of water supply pressure within experimental range.

Three-Dimensional Hydrodynamic Lubrication Analysis of Cylinder Liner-Piston Ring

This paper constructs a three-dimensional transient hydrodynamic lubrication model for cylinder liner-piston ring based on the three-dimensional transient average Reynolds equation and asperity contact model. A computer program was written with FORTRAN to calculate hydrodynamic lubrication, in which the surface roughness, the variable viscosity effect and the deformation of the circumferential direction of the cylinder liner are taken into account. The film pressure distribution in different crank angle during the stroke, minimum film thickness and friction are computed and analyzed with this program. This three-dimensional transient hydrodynamic lubrication model provides a design basis for the friction analysis of cylinder liner-piston ring.

The Effect of Surface Defect on EHL Point Contact

In this paper, the lubrication of three-dimensional EHL point contact with surface defect was solved, the lubrication film shape and film pressure distribution were presented and the characteristics of EHL point contact with defect were analyzed, the effect of surface defect on EHL point contact was studied. The results were presented that convex defect could lead to film pressure peak increasing, there was obvious micro-EHL effect, concave defect could lead to film pressure hollow and peak, film pressure peak was also increasing. The results also shown that convex and concave defects would have negative impact on EHL lubrication, there was great influence of surface defect on EHL lubrication pressure, the significant fluctuation of local film pressure was caused by surface defect, and generating greater pressure peak, maximum film pressure was rapid growth with the defect size increasing, so any kind defect should be to avoid in EHL lubrication.

The Influence of Micro-Texturing Dimple on the Bearing Capacity of the Elastohydrodynamic Lubrication Based on CFD-FSI Fluid-Solid Coupling

Based on the CFD-FSI fluid-solid coupled method, the equivalent elastohydrodynamic lubrication model of the micro-texturing dimple surface on the condition of the medium velocity and medium load, low velocity and heavy load, high velocity and heavy load, low velocity and light load and high velocity and light load is respectively solved by numerical method in this paper. And obtain the oil film pressure distribution curve and the oil the film thickness distribution curve on the conditions of steady state, and analyze the influence of micro-texturing dimples on the bearing capacity of the equivalent elastohydrodynamic lubrication model. Analysis results show that: compared with the corresponding minimum film thickness on the conditions of smooth surface, the minimum film thickness of micro-texturing dimple surface on the conditions of the medium velocity and medium load, low velocity and light load is increased, which indicates the bearing capacity of the equivalent elastohydrodynamic lubrication model of the micro-texturing dimple surface is increased; while the minimum film thickness of the rest conditions is decreased, which shows that the bearing capacity of the equivalent elastohydrodynamic lubrication model of the micro-texturing dimple surface is decreased. The study in this paper lays the foundation for the design and optimization of the micro-texturing dimple.

왕복동식 압축기의 저널 베어링 오일 패스 설계를 위한 연구

Because the performance of a reciprocating compressor in refrigeration and air-conditioning systems is influenced by the lubrication characteristics of sliding components, the lubrication characteristics between the crankshaft and journal bearing have to be researched for the design and the performance improvement of reciprocating compressors. Thus, the proper supply of lubricant for a lubrication between the crankshaft and journal bearing is essential, and an oil path for lubricant supply is installed in the shaft or bearing. However, in order to guarantee the lubrication performance of the journal bearing, it is necessary to design the position of the oil path. Therefore, it is studied to find the optimum position of the oil path by the analysis of the pressure distribution in the journal bearing. The results show that the position of the oil path is significantly influenced by the pressure distribution of the oil film in the journal bearing.

Numerical analysis on nanoparticles-laden gas film thrust bearing

Nanoparticles can be taken as additives and added into various fluids to improve their lubricating performances. At present, researches in this area are mainly concentrated on the improvement effects of nanoparticles on the lubricating performances of liquid such as oil and water. Nanoparticles will also affect gas lubrication, but few related studies have been reported. Nanoparticles-laden gas film (NLGF) is formed when adding nanoparticles into gas bearing. Then, the lubricating performances of gas bearing including pressure distribution and load-carrying capacity will change. The variations of pressure distribution and load-carrying capacity in nanoparticles-laden gas film thrust bearing are investigated by numerical method. Taking account of the compressibility of gas and the interactions between gas and nanoparticles, a computational fluid dynamics model based on Navier-Stokes equations is applied to simulate the NLGF flow. The effects of inlet nanoparticles volume fraction and orifice radius on film pressure distribution and load-carrying capacity of the NLGF are calculated. The numerical calculation results show that both of the film land pressure and the maximum film pressure both increase when the nanoparticles are added into gas bearing, and the film pressures increase with the rising of the inlet nanoparticles volume fraction. The nanoparticles have an enhancement effect on load-carrying capacity of the studied bearing, and the enhancement effect becomes greater as the film thickness decrease. Therefore, nanoparticles can effectively improve the lubricating performance of gas bearing. The proposed research provides a theoretical basis for the design of new-type nanoparticles-laden gas film bearings.

Stress Distribution Analysis on Alloy Layer of High Power Marine Diesel Engine Bearing Bush

According to the characteristics of large size, small clearance ratio, high oil film pressure and thin oil film thickness in the actual conditions of high power marine diesel engine bearing, this Paper analyzes oil film pressure distribution on inner surface of bearing bush based on the finite difference method, uses finite element method to establish the hierarchical model, and analyzes stress and strain distribution on bearing alloy. In addition, this Paper researches the changes of stress and strain distribution on bearing alloy layer when alloy layer thickness changes for the optimization design of high power marine diesel engine bearing bush.

Experimental Research on Film Pressure Distribution of Water-Lubricated Rubber Bearing With Multiaxial Grooves

In order to obtain the entire continuous circumferential film pressure distribution of a water-lubricated rubber bearing with multiaxial grooves, and further to study the bearing properties, an experimental research was conducted. The wireless measurement scheme was proposed, which can make the measurement process simple, convenient, and accurate. The unique design of the shaft and the installation methods for the pressure sensors are described. The time-domain averaging (TDA) algorithm was presented to suppress the random noises of the film pressure signal. By contrastive analysis on experimental results, some bearing properties, and working mechanism have been found and demonstrated.

Analysis of EHL Line Contact in Rapid Braking Motion

As is well known, almost all the machines need to start and brake. In this process, the lubrication state of their parts changes instantaneously. In this paper, an isothermal study for the line contact elastohydrodynamic lubrication (EHL), which is in rapid braking process and under a constant load, is carried out by using a simplified multigrid method. Numerical results indicate that the oil film thickness decreases and the oil film pressure increases with the decrease of the speed during the process of rapid braking. The oil film shrinks quickly and the oil entrapment occurs when the speed reduces to a certain range. Simultaneously, the distribution of oil film pressure tends to the central lubrication area. The size of the oil entrapment area and the changes of the oil film pressure are closely related to the braking time and the initial speed, which reflects the transient effects of the lubricating oil film.

Experimental research on air film formation behavior of air cushion belt conveyor with stable load

In this paper, the air film formation behavior of air cushion belt conveyor with stable load is studied. The air cushion field is analyzed by means of theoretical derivation, numerical simulation and experimental research. An intelligent experiment platform is developed. Three dimensional pressure distribution of air film and the air film thickness distribution along the conveyor belt in the width direction are obtained. The experimental result is analyzed by comparing with theoretical calculation and numerical simulation. The numerical and theoretical results are in good agreement with those obtained from experiments. The air film formation behavior pattern of air cushion belt conveyor with stable load is presented. The optimized film thickness and pore distribution are obtained based on the comprehensive energy consumption. This study provides a basis for the optimization design of air cushion belt conveyor.

Effects of Surface Roughness and Flow Rheology on the EHL of Circular Contacts with Power-law Fluid

The coupled effects of surface roughness and flow rheology on the Elastohydrodynamic lubrication (EHL) circular contact problems are analyzed and discussed. The average flow model is adapted for the interaction of the flow rheology of lubricant and surface roughness. The averaged Reynolds type equation, the rheology equations, the elastic deformation equation, and the force balance equation are solved simultaneously. The multilevel multi-integration (MLMI) algorithm and Gauss-Seidel iteration method are utilized to calculate the film thickness and pressure distributions. The effects of flow index, Peklenik number, and standard deviation of composite surface roughness on the film thickness and pressure distributions are discussed. The results show that the transverse type roughness and standard deviation of composite roughness enhance the pressure and film thickness in the central contact region. Moreover, the greater the flow index is, the greater the pressure distribution is in the central contact region, and the greater the film thickness is in all regions.