Thermal-EHD contacts lubricated with oil/refrigerant solutions: a new cavitation modeling approach based on refrigerant solubility

A first cavitation modeling with thermal effects for oil/refrigerant solutions lubricated ElastoHydroDynamic (EHD) point contacts is reported in this work. The solubility of the oil/refrigerant system is introduced into the Generalized Reynolds equation coupled with the elasticity equation and the energy conservation equation. The numerical results show a very good agreement with the published experimental results concerning film thickness prediction. Moreover, the present model describes the cavitation region on a physical basis. A discussion with other cavitation models from the literature is proposed. It puts into light the necessity of taking into account the solubility of the refrigerant into oil for such problems. Compared to pure oil, oil/refrigerant solutions can potentially reduce the amount of liquid oil for the next contact due to its higher cavitation intensity.

Assessment of artificial neural network for thermohydrodynamic lubrication analysis

Purpose In this study, artificial neural networks (ANNs) are constructed and validated by using the bearing data generated numerically from a thermohydrodynamic (THD) lubrication model. In many tribological simulations, a surrogate model (meta-model) for obtaining a fast solution with sufficient accuracy is highly desired. Design/methodology/approach The THD model is represented by two coupled partial differential equations, a simplified generalized Reynolds equation, considering the viscosity variation across the film thickness direction and a transient energy equation for the 3-D film temperature distribution. The ANNs tested are having a single- or dual-hidden-layer with two inputs and one output. The root-mean-square error and maximum/minimum absolute errors of validation points, when comparing with the THD solutions, were used to evaluate the prediction accuracy of the ANNs. Findings It is demonstrated that a properly constructed ANN surrogate model can predict the THD lubrication performance almost instantly with accuracy adequately retained. Originality/value This study extends the use of ANNs to the applications other than the analyses dealing with experimental data. A similar procedure can be used to build a surrogate model for computationally intensive tribological models to have fast results. One of such applications is conducting extensive optimum design of tribological components or systems. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2020-0109/

Derivation of the Reynolds equation in cylindrical coordinates applicable to the slipper/swash plate interface in axial piston pumps

Although many tribology references have presented the Reynolds equation in cylindrical coordinates, they may not be applicable to the slipper/swash plate interface in axial piston pumps due to complex macro and micro motions of slippers. Therefore, this paper derives the generalized Reynolds equation in cylindrical coordinates for this interface from momentum and continuity equations. Also, the boundary velocity conditions for the Reynolds equation are evaluated based on the kinematics of slippers, which accounts for the spinning motion. Compared with the traditional Reynolds equation for the slipper/swash plate interface, the new Reynolds equation in this work considers the geometric squeeze and centrifugal terms and has a different form of Couette terms.

Numerical optimization of surface texture for improved tribological performance of journal bearing at varying operating conditions

Purpose Journal bearings are used in numerous rotary machines. The load carrying capacity and friction of a bearing have been major concerns in design. Recent developments in surface texturing have showed potential outcomes to improve the tribological characteristics of mating surfaces. This study aims to investigate surface textures, which are transverse to the sliding direction, for frictional response of the journal bearing. Design/methodology/approach A hydrodynamic lubrication model is considered to evaluate the effect of surface texturing on the performance of a journal bearing at varying operating conditions. The two-dimensional generalized Reynolds equation, coupled with mass-conserving Elrod cavitation algorithm, is solved to evaluate texture-induced variations in tribological performance parameters. Findings Results have showed remarkable improvements in frictional response. Moreover, micro-textures on the journal surface alter the cavitation response and film-reformation in the hydrodynamic conjunction of the plain bearing. Originality/value Operating condition-based comprehensive exhaustive optimization of texture geometry is performed to generate widespread conclusion.

Spiral Bearing Lubrication with Viscosity Variation And Thermal Effect of Two Layer Fluid

In this paper a fluid film equation for two layer fluids and generalized Reynolds equation for convergent and divergent spiral bearing is derived with thermal effect. It is applied to see the effect of pre-load factor, viscosity variation, eccentricity, peripheral layer thickness. Expressions for load, pressure and coefficient of friction are derived and are analyzed numerically. The effect of pre-load factor analyzed for convergent and divergent spiral bearings. When pre-load factor is zero then both convergent and divergent spiral bearings are becomes journal bearing. It is observed the dimensionless load capacity values form the tables. The spiral bearing bears more load capacity than journal bearing. The effects of viscosity variation and thermal effect on these parameters are also analyzed.

A Comparison of the Roughness Regimes in Hydrodynamic Lubrication

This work relates to previous studies concerning the asymptotic behavior of Stokes flow in a narrow gap between two surfaces in relative motion. It is assumed that one of the surfaces is rough, with small roughness wavelength μ, so that the film thickness h becomes rapidly oscillating. Depending on the limit of the ratio h/μ, denoted as λ, three different lubrication regimes exist: Reynolds roughness (λ = 0), Stokes roughness (0 < λ < ∞), and high-frequency roughness (λ = ∞). In each regime, the pressure field is governed by a generalized Reynolds equation, whose coefficients (so-called flow factors) depend on λ. To investigate the accuracy and applicability of the limit regimes, we compute the Stokes flow factors for various roughness patterns by varying the parameter λ. The results show that there are realistic surface textures for which the Reynolds roughness is not accurate and the Stokes roughness must be used instead.

Numerical analysis and simulations of the magnetic field and hydrophobicity effect on the journal bearing dynamics

The article contains mathematical models of Reynolds equation with the effects of hydrophobicity of surface and magnetic field. The first section provides a new mathematical model of the solution of the generalized Reynolds equation and its application for a hydrophilic surface. It also derives a new boundary condition for the contact of a flowing liquid with a hydrophobic surface. This wettability condition is defined in dependence on the adhesion coefficient k. The second part presents mathematical models of Reynolds equation including the effect of hydrophobia and magnetic field. For all problems, the solutions are shown and the definitions of the stiffness and damping matrices of the liquid layer are outlined. From the results, it can be deduced that hydrophobic surface significantly affects the velocity profile of the liquid. It leads to a higher effect of the Lorentz force and thus of the magnetic field in comparison with a hydrophilic surface of the bearing lining.

Oil film boundary analysis of spiral oil wedge sleeve bearing based on the dynamic loading conditions

The area and location of cavitation change with time in the condition of dynamic loading. The cavitation location of sleeve bearing not only depends on axis location and velocity at a certain moment but also is affected by cavitation history, so the boundary condition need to be defined in the solution of lubrication equation. Based on the balance of axial inertia force, oil film force, and dynamic loading, the motion equation, generalized Reynolds equation and oil film thickness equation of spiral oil wedge sleeve bearing are established. The results show that the cavitation location and carrying capacity vary periodically with the change in time. The effect of dynamic loading and rotational speed on the oil film cavitation and carrying capacity is studied.

On the Influence of Thrust Bearings on the Nonlinear Rotor Vibrations of Turbochargers

This work investigates the influence of hydrodynamic thrust bearings on the lateral rotor oscillations. Four thrust bearing models are compared in terms of their predictions of the oil-film pressure (Reynolds equation), the oil-film temperature (energy equation) and the load capacity. A detailed thrust bearing model using the generalized Reynolds equation and the 3D energy equation, a model using the standard Reynolds equation with a 2D energy equation, a model where the standard Reynolds equation and the 2D energy equation are decoupled and finally an isothermal thrust bearing model are presented. It is shown that in lower rotational speeds, the four models produce almost the same results. However, as the rotational speed is increased, the necessity for a thermo-hydrodynamic model is demonstrated. Run-up simulations of a turbocharger rotor/bearing system are performed, using an isothermal thrust bearing model with different inlet oil-temperatures. The influence of the oil-temperature of the thrust bearing on the subsynchronous rotor oscillations is investigated. Finally, a thermo-hydrodynamic model is compared with an isothermal in run-up simulations, where the influence of the variable oil-viscosity is discussed.

A Thermohydrodynamic Coupling Model of Oil Aeration Turbulent Lubrication for Journal Bearing With Interface Effect

Oil aeration lubricant in high-speed journal bearing is composed of mixture of continuous phase liquid and discrete phase bubbles. This work establishes a thermohydrodynamic (THD) coupling model for this lubrication condition. The generalized Reynolds equation is derived by the continuity equation, Navier–Stokes equation, law of wall turbulence model, and bubble volume distribution function, and then a THD oil aeration turbulent lubrication model is established by coupling the generalized Reynolds equation, energy equation, force equilibrium equation of bubble, and population balance equations (PBEs). The coupled-equations are solved numerically to obtain the pressure distribution under oil aeration lubrication state, the equilibrium distribution of bubble volume, the turbulent velocity distribution, the bubble velocity distribution, and the temperature rise. The results show that the load capacity of a bearing with oil aeration lubrication model is higher than that of the same bearing with a pure oil lubrication model, and heat dissipation performance of the bearing under the oil aeration lubrication state is superior.