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Computational fluid dynamics and full elasticity model for sliding line thermal elastohydrodynamic contacts

**总被引：1，自引：0，他引：1**Classically, the EHD problem is solved using the Reynolds assumptions to model the fluid behaviour, and the Boussinesq elastic deformation equation to model the solid response, both being coupled with the load balance equation. The development of an alternative approach is presented here in order to solve at once the Navier-Stokes equations (mass conservation and momentum equilibrium), the full elasticity and energy equations for the line EHD problem in a fluid-structure interaction approach.The Finite Element Method is used to solve the mathematical formulation in a fully coupled way, inspired from Habchi et al. (2008) [1]. After linearisation with the Newton procedure, all the physical quantities (pressure, velocity field, deformations and temperature) are solved together in a unique system. An important benefit of this approach is the possibility to implement in a simple manner the non-Newtonian and thermal effects; in fact all the quantities can vary through the film thickness. The extension to non-Newtonian rheology and the pressure and temperature dependencies for the viscosity and density are taken into account in a direct way to allow an acceptable prediction of the friction coefficient. Gradients across the film thickness and temperature fields in both the fluid and the two solids are naturally computed and analysed. As a case study, we focus first on the pure sliding cylinder-on-plane contact. It is shown that thermal effects due to friction in the central zone of the contact play a role in heating the lubricant at the inlet zone, via heat conduction in the solids. By increasing the Slide-to-Roll Ratio (SRR), the occurrence of dimples and the subsequent effects in different parts of the contact under zero entrainment velocity conditions are then studied. 相似文献

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Effect of geometrical parameters in micro-grooved crosshatch pattern under lubricated sliding friction

**总被引：1，自引：0，他引：1**Tribological test was carried out using a pin-on-disc geometry with textured SKD11 pin on bearing steel disc, under sliding in paraffin oil. Micro-grooved crosshatch pattern has been fabricated with various angles and widths. The effects of geometrical parameters on friction were mainly examined in mixed and elastohydrodynamic lubrication. The results show that friction control can be achieved by fabricating the micro-grooved crosshatch pattern on a contact surface. It is observed that each geometrical parameter of texture influence on friction, especially decrease of groove aspect ratio and increases of groove sliding length show friction reduction performance. Crucial parameter

*G*was proposed for micro-grooved crosshatch texture. The friction mechanism is explained by micro fluid flow with limited theoretical approach. 相似文献_{l}4.

The complicated nature of the EHL-problem has so far forced researchers to develop their own computer codes. These codes are ultimately based on the Reynolds equation, and if thermal EHL-simulations are required, a simultaneous solution of the equation of energy also has to be performed. To date only a few attempts to solve the full equations of momentum and continuity as well as equations of energy have been performed. However, such an approach will give extended possibilities of simulating EHL-contacts; i.e. the computational domain can be expanded and it will be possible to simulate the flow, not only in the contact but also around the contact. Another possibility is to investigate how the altering length scales of the surface roughness influence the behaviour of the flow in the contact. However, the aim of the work presented in this paper is to investigate the possibilities of using a commercial CFD-code (computational fluid dynamics code) based on the above-mentioned equations for simulating thermal EHL. The rheology is assumed to be Newtonian and the equations of momentum and continuity are then commonly referred to as the Navier–Stokes equations (N–S equations). The geometry chosen for the simulations is a smooth line contact geometry, for which the results from the simulations show that it is possible to use the N–S equations for thermal EHL for contact pressures up to approximately 0.7 GPa. The code used in this work is the commercial CFD software (CFX 4.3 user guide). There is a limitation in the N–S approach due to a singularity that can occur in the equation of momentum when the principal shear stresses in the film become too high. However, a thermal approach makes it possible to simulate EHL-contacts at higher loads compared with an isothermal approach, due to the reduction of the viscosity in the former approach. The singularity is not present in the Reynolds approach. 相似文献

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Traction machines have been frequently used to study the rheological responses of lubricants in elastohydrodynamic lubrication (EHL) contacts. Fundamental properties are inferred from EHL traction measurements based on the average pressures and temperatures in the contact. This average approach leads to uncertainty in the accuracy of the results due to the highly nonlinear resonse of the fluid such as viscosity to both pressure and temperature. A non-averaging method is developed in this paper to study the elastic and plastic properties of traction fluids operating in EHL contacts at small slide-to-roll ratios. A precision line-contact traction rig is used to measure the EHL traction at a given oil temperature and Hertz pressure. By choosing a sensible pressure-property expression, the parameters of the expression can be determined through the initial slope and peak traction coefficient of the traction measurements. The elastic shear modulus and the limiting shear stress of the lubricant corresponding to a single pressure can then be calculated for a range of pressures and temperatures of practical interest. Two high-traction fluids are studied, and their elastic moduli and limiting shear stresses presented. 相似文献

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The problems of elastic-hydrostatic lubrication (EHL) are discussed here from the mathematical and mechanical point of view. We begin with the formulation of the Reynolds equation and derive analytical solutions of the tilting plate and the disc models. We show that the so-called “Pressure spike” cannot be observed analytically and numerically by the newly developed computer codes, which is a reasonable simulation of one-dimensional flow from a mechanical point of view. Then, we discuss the possible factors that may be responsible for generating the conventional pressure spike including some unreasonable assumptions incorporated in formulating the numerical equation and in coding the computer program. A small pressure projection, however, has been experimentally observed. Therefore, some possible mechanical and mathematical explanations for it will be presented in a series of our subsequent papers. 相似文献

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This work deals with the mathematical modelling of multibody systems interconnected via thin fluid films. The dynamics of the fluid films can be actively controlled by means of different types of actuators, allowing significant vibration reduction of the system components. In this framework, this paper gives a theoretical contribution to the combined fields of fluid–structure interaction and vibration control. The methodology is applied to a reciprocating linear compressor, where the dynamics of the mechanical components are described with help of multibody dynamics. The crank is linked to the rotor via a thin fluid film, where the hydrodynamic pressure is described by the Reynolds equation, which is modified to accommodate the controllable lubrication conditions. The fluid film forces are coupled to the set of nonlinear equations that describes the dynamics of the reciprocating linear compressor. The system of equations is numerically solved for the case when the system operates with conventional hydrodynamic lubrication and for several cases of the bearing operating under controlled hybrid lubrication conditions. The analysis of the results is carried out with focus on the behaviour of the journal orbits, maximum fluid film pressure and minimum fluid film thickness. 相似文献

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This paper presents the influence of aging the nitrile rubber, the most popular seal material, in various base fluids on sliding friction and abrasive wear. The lubricants used are synthetic esters, natural esters, different types of mineral base oils, poly-α-olefins and very high viscosity index oils. Friction has been studied for two directions of motion with respect to lay on the elastomer sample by using the SRV Optimol test machine. These findings show that as compared to all other lubricant formulations, ageing the elastomer in polyol ester leads to the maximum reduction of friction coefficient especially in perpendicular sliding to the initial lay on the surface. The abrasive wear studies were carried out by using a two-body abrasive wear tester against dry and lubricated elastomer. It was interesting to note that two-body abrasive wear of elastomeric material was higher during rubbing in presence of the fluids as compared to that in dry condition. Further, aging the elastomer in these base fluids especially in ester base fluids, results in more abrasive wear. 相似文献

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P. P. Usov 《Journal of Friction and Wear》2008,29(1):54-65

A mathematical model is proposed of the process of formation of the elastohydrodynamic (EHD) lubricant layer between resilient cylinders that begin to rotate in the lubricating material medium from the resting state. The model assumes division of the whole contact region into three zones: the zone within which dry motion is described by the equations of the elastohydrodynamic theory of lubrication, the transient zone, and the dry contact zone. The method of the numerical solution of this system of equations is presented. The calculations are performed for the lubricating material that was used in the published experimental study of the process of formation of the EHD lubricating layer between the resilient ball and the flat resilient base. It is shown that the calculation results well agree with the experimental data both qualitatively and quantitatively providing that the transient region dimensions are adequately selected. The function of the pressure distribution, the lubricating layer thickness, the lubricating material flow, the rate of approach of the surfaces over the contact region at different moments of time, the time dependencies of the lubricating layer thickness at different points of the contact region, and the coordinates of the boundary points of the dry contact region is also presented. 相似文献

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