Thermohydrodynamic Lubrication Research Articles

Numeric based low viscosity adiabatic thermo-tribological performance analysis of piston-skirt liner system lubrication at high engine speed

Abstract In conjunction with lubricant oil film dynamics, automotive piston's primary and secondary motion indicatively affect the engine noise and frictional losses (fuel economy). The escalation of oil film temperature due to adiabatic shear heating of low viscosity Newtonian lubricant oil film affects the load carrying capacity and viscosity of lubricating film and enhances friction losses, piston wear, and non-linear lateral motion of piston. In this study, a numerical model for piston dynamic and lubrication is presented, in which adiabatic heating effects are simulated in hydrodynamic mixed lubrication regime by coupling with 2D-energy equation. The thermo-hydrodynamic lubrication model is solved using finite difference formulation, while the piston dynamic model is solved using the modified Newton Raphson method. Furthermore, the effect of adiabatic shearing of lubricant and piston skirt design parameters on piston dynamics and lubrication performance are analyzed. Results show that the adiabatic heating significantly affects piston lateral motion and lubrication performance. Lubrication analysis is very beneficial in the improvement of engine design of piston skirt-liner and can help reduce the friction losses.

Thermohydrodynamic lubrication model of a slipper in swashplate type axial piston machines - validation through experimental data

A thermohydrodynamic lubrication (THL) model of hybrid (hydrostatic and hydrodynamic) thrust bearings, which is applicable to slippers of swashplate type axial piston pumps and motors, was validated by experimental results. The model consisted fundamentally of the generalised Reynolds equation, three-dimensional energy equation, and the heat conduction equation. The numerical calculation was performed in fluid film lubrication under the experimental conditions and the solutions were compared with the data. Reverse flow and oil mixing were considered in solving the energy equation. The comparison of the temperature distributions and centre clearances was made at supply pressures up to 35 MPa and rotational speeds up to 26.7 s–1. The simulation showed good agreement with the experiment and the theoretical model was validated.

Thermohydrodynamic analysis of high speed water-lubricated spiral groove thrust bearing considering effects of cavitation, inertia and turbulence

Abstract A thermohydrodynamic cavitating flow lubrication model including effects of cavitation, inertia and turbulence for high speed water-lubricated spiral groove thrust bearing was established. The static characteristics of the water-lubricated spiral groove thrust bearing at high speed condition were investigated using this model. The numerical calculation results have shown that load carrying capacity and friction torque reduce due to inertia and cavitation in high speed condition, while that load carrying capacity and friction torque increase due to turbulence. The maximum temperature rise increases due to inertia effect, and reduces due to cavitation effect. In addition, the influence of inertia effect on the static characteristics of water-lubricated spiral groove thrust bearing was greater than the cavitation effect under high speed condition.

Transition to thermohydrodynamic lubrication problem

We consider a non-isothermal Stokes equation used to calculate the pressure distribution in a thin layer of lubricant film between two surfaces. The problem is described in 2D and 3D settings by the Stokes and heat transfer equations. Under appropriate regularity assumptions on the data, existence results for the non-isothermal Stokes is recalled. Using a formal asymptotic expansion, we obtain a generalized Reynolds equation coupled with a limit energy equation, the so-called non-isothermal Reynolds system. Then existence and uniqueness are proved for this system by using a fixed-point argument. Finally, a rigorous justification of the convergence is established.

Study on Static Thermo-hydrodynamic Lubrication of Floating Ring Bearing

Study on Static Thermo-hydrodynamic Lubrication of Floating Ring Bearing

Equivalent Clearance Model for Solving Thermohydrodynamic Lubrication of Slider Bearings With Steps

This study focuses on the thermohydrodynamic lubrication (THD) analysis of fluid film bearings with steps on the bearing surface, such as Rayleigh step. In general, the Reynolds equation does not satisfy the continuity of fluid velocity components at steps. This discontinuity results in the difficulty to solve the energy equation for the lubricants by finite differential method (FDM), because the energy equation needs the velocity components explicitly. The authors have solved this issue by introducing the equivalent clearance height and the equivalent gradient of the clearance height at steps. These parameters remove the discontinuity of velocity components, and the Reynolds equations can be solved for any bearing surfaces with step regions by FDM. Moreover, this method results in pseudocontinuous velocity components, which enables the energy equation to be solved as well. This paper describes this method with one-dimensional and equal grids model. The numerical results of pressure and temperature distributions by the proposed method for an infinite width Rayleigh step bearing agree well with the results obtained by solving full Navier–Stokes equations with semi-implicit method for pressure-linked equations revised (SIMPLER) method.

3-D thermohydrodynamic analysis of textured, grooved, pocketed and hydrophobic pivoted-pad thrust bearings

In the present study, a computational investigation of thermohydrodynamic lubrication in pivoted-pad thrust bearings exhibiting different types of surface treatment is presented. Five different types of pivoted-pad thrust bearings are cross-evaluated for operation at different combinations of thrust load and rotational speed: (a) a pocket bearing, (b) a bearing with circumferential grooves, (c) a bearing with radial grooves, (d) a bearing with rectangular texturing, and (e) a hydrophobic bearing. A parametric analysis is conducted to identify the effect of the main design parameters (machining depth, radial/circumferential machining extents, slip length, radial/circumferential hydrophobic extents) on bearing performance. The performance gains obtained by each surface treatment type are evaluated against the performance of a conventional plain bearing of the same principal dimensions.

Experimental researches of the hybrid Rayleigh step bearing

The experimental researches for hybrid Rayleigh step bearing at the different regimes of exploitation are investigated. Comparative analysis and the analysis of test data with theoretical calculations of the bearing static characteristics on the basis of thermohydrodynamic lubrication equalizations were carried out. The fundamental aspects of the test, concerning to hybrid bearing, the test procedure at the experimental facility, installed sensors taring, controlling and reading are determined

THD Analysis of Rolling Piston and Journal Bearings in Rotary Compressors

ABSTRACTA numerical analysis of the thermohydrodynamic lubrication of a rolling piston and two misaligned journal bearings in a rotary compressor has been carried out. The temperature rise of the oil film was calculated according to the transient energy equation of viscous fluid, and coupled analysis with the hydrodynamic lubrication of the rolling piston and journal bearings was conducted by using the finite element method and finite difference method. The distributions of the pressure and temperature rise of the oil film for several cycles were calculated. The analysis results show that for the journal bearings, the temperature of the oil film rises with the increase in pressure, the highest temperature appears around the region of the maximum pressure, whereas for the rolling piston bearing, there is a sharp peak in the temperature distribution. The maximum temperature in the oil film varies periodically with the rotation of the crankshaft, and after several cycles the balance between viscous heating and heat dissipation is achieved. The thermal analysis results were compared with those of the isothermal analysis. It is found that the difference in lubrication performance between the thermal and isothermal cases is relative small, due to the mild temperature rise in the bearing system.

Solving a thermohydrodynamic lubrication problem for complex-loaded sliding bearings with allowance for rheological behavior of lubricating fluid

A method for calculating thermohydrodynamic characteristics of complex-loaded sliding bearings is considered. The non-Newtonian behavior of a fluid, as well as processes of heat transfer between a lubricating film and surrounding moving surfaces of the tribojoint, are allowed for. Results of calculating hydromechanical characteristics of a connecting-rod bearing of an internal combustion engine are presented.

Surface Texturing한 평행 스러스트 베어링의 열유체윤활 해석: 딤플 반경과 깊이의 영향

School of Mechanical Engineering, ERI, Gyeongsang National University(Received July 19, 2014 ; Revised August 20, 2014 ; Accepted August 22, 2014)Abstract − In order to reduce friction and improve reliability, researchers have applied various surface texturingmethods to highly sliding machine elements such as mechanical seals and piston rings. Despite extensive the-oretical research on surface texturing, previous numerical results are only applicable to isothermal and iso-vis-cous conditions. Because the lubricant flow pattern of textured bearing surfaces is much more complicated thanthat for non-textured bearings, the Navier?Stokes equation is more suitable than the Reynolds equation for theformer. This study carries out a thermohydrodynamic (THD) lubrication analysis to investigate the lubricationcharacteristics of a single micro-dimpled parallel thrust bearing cell. The analysis involves using the continuity,Navier?Stokes, energy, temperature?viscosity relation, and heat conduction equations with the commercial com-putational fluid dynamics (CFD) code FLUENT. This study discretizes these equations using the finite volumemethod and solves them using the SIMPLE algorithm. The results include finding the streamlines, pressure andtemperature distributions, and variations in the friction force and leakage for various dimple radii and depths.Increasing the dimple radius and decreasing the depth causes a recirculation flow to form because of a strongvortex, and the oil temperature greatly increases compared with the non-textured case. The present numericalscheme and results are applicable to THD analysis of various surface-textured sliding bearings and can lead tofurther study. Keywords − dimple (딤플), friction reduction (마찰저감 ), parallel thrust bearing (평행 스러스트 베어링 ), surfacetexturing (표면조직가공), thermohydrodynamic lubrication (열유체윤활)

Multiscale simulation for thermo-hydrodynamic lubrication of a polymeric liquid between parallel plates

Thermo-hydrodynamic lubrication of a polymeric liquid composed of short chains between parallel plates is analysed by a multi-scale simulation, i.e. the synchronised molecular dynamics simulation via macroscopic heat and momentum transfer, which has been recently developed by us. The rheological properties and conformation of polymer chains coupled with the temperature rise caused by local viscous heating are investigated with a non-dimensional parameter, i.e. the Nahme–Griffith number, which is defined by the ratio of the viscous heating to the thermal conduction at the characteristic temperature required to sufficiently change the viscosity. The present simulation demonstrates that strong shear thinning and transitional behaviour of the conformation of the polymer chains occurs with a rapid temperature rise when the Nahme–Griffith number exceeds unity.

Centrifugal effects on the dynamic characteristics of high speed hydrostatic thrust bearing lubricated by low viscosity fluid

The effect of the centrifugal force of the fluid film on the performance of the high speed hydrostatic thrust bearing lubricated by low viscosity fluid cannot be neglected. Considering the centrifugal inertia effect, concentrated inertia effect at the recess edge, and the misalignment effect, the thermo-hydrodynamic lubrication model is established by using the reduced Navier–Stokes equation, the energy equation, and the bulk flow theory. The effects of centrifugal forces on dynamic performances of the high speed thrust bearing with different supply pressures and rotational speeds have been analyzed systematically. The results show that the centrifugal force reduces the axial and angular stiffness and hardly affects the damping coefficients; the centrifugal effects decrease with the increasing of eccentricity ratio and misalignment angle.

Some aspects of lubrication in heavy regimes: Thermal effects, stability and turbulence

In this work, a combination of numerical methods applied to thermohydrodynamic lubrication problems with cavitation is presented. It should be emphasized the difficulty of the nonlinear mathematical coupled model involving a free boundary problem, but also the simplicity of the algorithms employed to solve it. So, finite element discretizations for the hydrodynamic and thermal equations combined with upwind techniques for the convection terms and duality methods for nonlinear features are proposed.Additionally, a model describing the movement of the shaft is provided. Considering the shaft as a rigid body this model will consist of an ODE system relating acceleration of the center of gravity and external and pressure loads. The numerical experiments of mechanical stability try to clarify the position of the neutral stability curve.Finally, a rotating machine for ship propulsion involving both axial and radial bearings operating with nonconventional lubricants (seawater to avoid environmental pollution) is analyzed by using laminar and turbulent inertial flows.

Evaluation of the Thermal Effects in Tilting Pad Bearing

The analysis of thermal effects is of expressive importance in the context of rotordynamics to evaluate the behavior of hydrodynamic bearings because these effects can influence their dynamic characteristics under specific operational conditions. For this reason, a thermohydrodynamic model is developed in this work, in which the pressure distribution in the oil film and the temperature distribution are calculated together. From the pressure distribution, the velocity distribution field is determined, as well as the viscous dissipation, and consequently, the temperature distribution. The finite volume method is applied to solve the Reynolds equation and the energy equation in the thermohydrodynamic model (THD). The results show that the temperature is higher as the rotational speed increases due to the shear rate of the oil film. The maximum temperature in the bearing occurs in the overloaded pad, near the outlet boundary. The experimental tests were performed in a tilting pad journal bearing operating in a steam turbine to validate the model. The comparison between the experimental and numerical results provides a good correlation. The thermohydrodynamic lubrication developed in this assignment is promising to consistently evaluate the behavior of the tilting pad journal bearing operating in relatively high rotational speeds.

Optimum shape design for surface of a thermohydrodynamic lubrication slider bearing

ABSTRACTThis paper utilises a thermohydrodynamic model of bearing to optimise the shape of slider bearing. Friction is minimised subject to load and centre of pressure requirements using a sequential quadratic programming algorithm. A generalised Reynolds equation is solved simultaneously with an energy equation using the finite volume method to obtain bearing characteristics, such as friction, load and centre of pressure. Results show that the coefficient of friction is reduced by the optimisation approach. Results also show that larger temperature–viscosity coefficient and inlet viscosity tend to yield smaller optimal friction, whereas larger thermal conductivity tends to yield larger optimal friction. Copyright © 2012 John Wiley & Sons, Ltd.

고속 열유체 저어널 베어링에서 단일유체로서의 다등급 엔진 오일과 그 첨가액체들의 혼합물에 대한 성능 비교

Dept. of Automotive Engineering, Hoseo University(Received February 7, 2012; Revised March 4, 2012; Accepted March 5, 2012)Abstract − To product multi-grade oil like engine oil, a sort of mineral base oil is mixed with a fundamentaladditive liquid package and a polymer liquid as viscosity index improver in order to improve the lubricatingproperty of oil. That is, engine oil is the mixture of more than two fluids. In this paper, it will be systematicallyorganized the governing equation describing non-Newtonian thermo-hydrodynamic lubrication related with themixture of incompressible fluids based on the principle of continuum mechanics. Then, in order to find howthe thermal analysis effect on the bearing performance lubricated with the mixture of multi-fluids, it will becompared to the performances between the mixture of each liquid to be blended and multi-grade engine oil asa single fluid in a high speed journal bearing. It is found that, in the case of lower viscosity oil, the differenceof pressure distribution between the above two cases turns out to be existed, even if the load capacity is samelevel.Keywords − mixture of fluids(유체의 혼합물), homogenous liquid(균질액), mineral base oil(광유 기유),additive liquid package(첨가제용 액체 패키지), polymer liquid for viscosity index improver(점도지수개선용 중합액체), multi-grade engine oil(다등급 엔진오일), non-newtonian fluid(비-뉴톤 유체), high speedjournal bearing(고속 저어널 베어링), thermo-hydrodynamic lubrication(열유체윤활)

A General Thermohydrodynamic Lubrication Model for Laminar, Transitional and Turbulent Slider Bearings

A General Thermohydrodynamic Lubrication Model for Laminar, Transitional and Turbulent Slider Bearings

엔진오일에 물이 혼합될 때 터보챠져 저어널 베어링의 열유체윤활 해석

Abstract : In this study, using the governing equation for thermohydrodyamic lubrication involving the homogeneous mixture of incompressible fluid derived by based on the principle of continuum mechanics, it is discussed the effects of water within engine oil on the performance of high speed journal bearing of a turbocharger. The governing equations are the general equations being able to be applied on the mixture of Newtonian fluid and non-Newtonian fluid. Here, the fluid viscosity index, n of power-law non-Newtonian fluid is supposed to be 1 for the application of the journal bearing in a turbocharger lubricated with the mixture of two Newtonian fluid, for example, water within engine oil. The results related with the bearing performance are shown that the bearing friction is to decrease and the side leakage and bearing load increase as increasing the water content in an engine oil. Key words : Mixture of two fluids( 두 유체의 혼합물), Thermohydrodynamic lubrication( 열유체윤활), Emulsion( 유상액), Homogeneous liquid(균질액)

Adaptive Multi-Objective Optimum Design of Journal Bearing Based on a Back-Stepping Approach

This article describes an adaptive multi-objective optimization journal bearing design method based on a back-stepping approach. Thermohydrodynamic lubrication analysis was used for accurate prediction of lubricant flow and power loss. The multi-objective optimization design method based on a back-stepping method was used to search for the optimum journal bearing design that can adaptively identify the equilibrium position of journal bearings and avoid iteration for the calculation of the equilibrium position of journal bearings. In the optimum journal bearing design, design variables such as radius, bearing length, radial clearance, journal eccentricity ratio, and attitude angle are used to simultaneously minimize oil flow and power loss. Comparisons between the adaptive optimization method and the conventional iteration method show that the proposed method can reduce the computational time of the optimization procedure, and the ability to find a diverse set of solutions was improved with the adaptive optimization methodology.