Thermohydrodynamic Lubrication Model Research Articles

Study on rotor-bearing dynamic performance of a novel motorized spindle supported by water-lubricated hydrodynamic spiral grooved bearings

The water-lubricated hydrodynamic spiral grooved bearings have been utilized to support the high-speed motorized spindle. However, the viscous damping effect of water is much weaker than that of the oil, so the dynamic behavior and the stability of the motorized spindle with the water-lubricated spiral grooved bearings need to be studied thoroughly. This paper established an improved rotor-bearing dynamic model for the motorized spindle by incorporating both the distributed effect of journal bearing and the tilting effect of thrust bearing into a turbulent thermohydrodynamic lubrication model. An experimental setup for the motorized spindle was developed to measure the spindle dynamic behaviors and verify the established dynamic model. The critical speeds, the transient dynamics and the stability of the motorized spindle are studied theoretically and experimentally. The results show that the motorized spindle with the water-lubricated spiral grooved bearings can operate at high speeds with a satisfactory supporting stiffness and exhibits an excellent operational stability.

The effects of bubble evolution and oil shear thinning on the static behavior of bubbly oil lubricated bearing

Bubble evolution and shear thinning effect are main factors affecting lubrication behavior of bubbly oil. In this study, a thermohydrodynamic lubrication model for the bubbly oil considering the bubble evolution and the shear thinning effect was established based on the multiphase mixtures theory. The influence of bubble evolution and shear thinning effect on the static behavior of bubbly oil lubricated bearing was analyzed, and an experimental study was conducted to verify the model. The result shows that the bubble radius is mainly dependent on the liquid pressure; the bearing static behavior is affected by the bubble evolution through the interface effect; the shear thinning effect of the pure oil can be enhanced with regarding the bubble evolution effect.

A Mixed Lubrication Deterministic Model of an Elastic Support Water-Lubricated Tilting Pad Thrust Bearing

In order to study the effect of surface roughness on lubrication performance of an elastic support water-lubricated tilting pad thrust bearing, a mixed lubrication (ML) deterministic model is hereby presented based on a unified Reynolds equation model. This very model incorporates the elastic–plastic deformation of asperities and polymer matrix of the thrust pad, as well as the elastic deformation of the rubber support. The randomly distributed surface roughness of the thrust pad is generated by a mathematical model and shares the same distribution characteristics as the measured surface roughness. The Greenwood and Williamson asperity contact model and thin plate deformation model are combined to solve the asperities contact stress and deformation. Meanwhile, the bearing ML performance is compared with the results calculated by a thermohydrodynamic (THD) lubrication model and a thermo-elasto-hydrodynamic (TEHD) lubrication model, while the film thickness is also compared with measurements. The results show that the water film thickness calculated by the ML model is smaller than that by the THD model and the TEHD model, but the water film temperature is higher. The roughness has a great influence on the contact area ratio and the lubrication state, but little effect on the average film thickness. A higher roughness indicates a higher rotational speed required for the bearing to achieve full hydrodynamic lubrication. The film thickness calculated by the mixed lubrication model is closer to the measured results. Overall, it is proved that the mixed lubrication model can more accurately predict the lubrication performance of bearings. Compared to the thin plate deformation model, the elastic deformation simulation based on the half-infinite space model severely overestimates the elastic deformation of the pad surface, making it unsuitable for calculating the elastic deformation of the polymer matrix of the thrust pad under contact force or water film pressure. This ML deterministic model provides an effective means for high-precision prediction of the lubrication performance of the elastic supported water-lubricated thrust bearings coupled with multi-layer soft materials.

Time History of Maximum Bearing Temperature Based on a Simplified Thermohydrodynamic Lubrication Theory

An overshoot phenomenon of bearing temperature in hydrodynamic journal bearings may be observed during a sudden start-up experiment. This phenomenon implies that the maximum bearing temperature in acceleration operation may exceed the predicted one which can be predicted accurately by applying a state-of-the-art steady state thermohydrodynamic lubrication (THL) model. This paper presents the maximum bearing temperature including the one during acceleration operation by using a simplified THL model that is newly proposed for a transient THL analysis. It is found that the overshooted temperature can be qualitatively predicted by using the transient THL model that incorporates properly the interaction between the motion of journal center and the viscous dissipation, even if it is a simple model. Next, the transient temperature during slow acceleration operation and also those toward higher dimensional steady state journal rotational speed are calculated and they are found to be in qualitative agreement with the measurements. The oil film characteristics such as oil film pressure, temperature and thickness after reaching the steady state equilibrium do not depend on the value of initial journal eccentricity ratio in the transient analysis. However, when the values are different, the characteristics immediately after starting rotation change largely. In the case of the value 1.00, it is found to give a prediction that agrees qualitatively with the characteristics measured in the experiment.

A New Design Method of Cylindrical Bearings Based on a Simplified Thermohydrodynamic Lubrication Model

A New Design Method of Cylindrical Bearings Based on a Simplified Thermohydrodynamic Lubrication Model

A simplified thermohydrodynamic lubrication model for application to the design of cylindrical journal bearings with two-axial oil grooves

A simplified thermohydrodynamic lubrication model for application to the design of cylindrical journal bearings with two-axial oil grooves

Influence of Injection Pressure on the Thermohydrodynamic Behavior of Tilting Pad Journal Bearings—Model and Experiment

In rotating machines, tilting pad journal bearings (TPJBs) are widely used because of their enhanced design stability in comparison with alternative bearing configurations. In the present research, a thermohydrodynamic (THD) lubrication model for a tilting pad bearing with injection is developed. Within the THD lubrication model, the lubricant is also fed into each pad through a central injection orifice. The effects on the lubricant oil film pressures and temperatures and subsequent influences on the system dynamic behavior were investigated. Another important factor considered within the THD model is associated with the flexibility of the pivot of each pad and its impact on the behavior of the bearing when subjected to direct lubricant injection. The numerical model results are compared with the measurements of the rotor equilibrium position within the bearing and the pad temperatures obtained from the test rig designed specifically for the TPJB geometry with and without central pad injection. Pad temperatures are measured before the injection orifice position and after it. Agreement between experimental and model-predicted results provides confidence in the model’s ability to evaluate the dynamic behavior of the bearing and its effect on the complete system through the stiffness and damping coefficients.

Comparative Study on Static Characteristics of Double-Pad Inwardly and Outwardly Pumping Water-Lubricated Spiral-Groove Thrust Bearings

Abstract The purpose of this technical brief is to investigate comparatively the static characteristics of the double-pad inwardly pumping and outwardly pumping water-lubricated spiral-groove thrust bearings (SGTBs). Firstly, a thermo-hydrodynamic lubrication model including the cavitating, centrifugal, and turbulent effects is established for the double-pad water-lubricated SGTB operating at a high-speed condition. Subsequently, the film thickness and volume flowrate are verified by an experimental study for the high-speed water-lubricated SGTBs. Finally, the effects of the operating conditions and configuration parameters on the static characteristics of the double-pad inwardly pumping and outwardly pumping SGTBs are analyzed systematically. The simulated results show that when the radius ratio exceeds 0.7, the outwardly pumping SGTB can perform better than the inwardly pumping version, with good axial load capacity, higher resistance to tilting and always positive radial flowrate.

A New Design Method of Cylindrical Bearings Based on a Simplified Thermohydrodynamic Lubrication Model

A New Design Method of Cylindrical Bearings Based on a Simplified Thermohydrodynamic Lubrication Model

Thermohydrodynamic Characteristics and Stability Analysis for a Journal Hybrid Floating Ring Bearing Within Laminar and Turbulent Mixed Flow Regime

Abstract There exist laminar and turbulent flow in the inner and outer fluid film of the hybrid floating ring bearing at high speed. The finite element method (FEM) and finite difference method (FDM) are used to solve the thermohydrodynamic (THD) lubrication model within the laminar and turbulent mixed flow regime which governs the pressure, temperature, viscosity, and Reynolds number of the two-layer fluid films together for a type of the journal hybrid floating ring bearing with deep/shallow pockets. The static and dynamic characteristics are analyzed including the load capacity, the friction moment, the volume flowrate, the stiffness, and damping coefficients with consideration of the mixed flow and thermal effect based on the floating ring balance. The unitized kinematic model of the shaft and floating ring is proposed to deduce the instability criteria and calculate the threshold rotational speed of a rigid Jeffcott rotor system supported on two hybrid floating ring bearings by the Routh–Hurwitz method. The results present that there are non-uniform pressure and temperature profile within the fluid film field, and the laminar flow and turbulent flow appear at certain positions of film through theory and experiment, separately. The mixed flow effect promotes the bearing load capacity and the friction moment at high speed and eccentricity, and the system threshold speed drops within the mixed flow regime. Therefore, the thermal effect and mixed flow existing in the fluid film should be considered into the lubrication analysis for the floating ring bearing.

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/

Thermohydrodynamic Model of Cavitating Flow and Dynamic Characteristic Calculation for High-Speed Water-Lubricated Pump-Out Spiral Groove Bearing

A complete thermohydrodynamic lubrication model for pump-out spiral groove thrust bearings (SGTB) with cavitating flow is established based on two-phase flow and transport theory. Various effects (cavitating flow interface effect, convective heat transfer effect, heat conduction effect, inertia effect, breakage and coalescence of bubbles) of water lubricant at high speed are included when modeling. The bubble size distributions, bubble number density of the cavitating flow, and the dynamic coefficients of the SGTB are predicted using this model. The probability distribution of the bubble size, bubble number density, and axial film stiffness coefficient agree with the experimental values. The results show that the number of small-sized bubbles is much larger than the number of large-sized bubbles in cavitating flow. When the SGTB has a specified spiral angle, the direct stiffness coefficients increase and the cross-stiffness coefficients decrease due to the cavitation effect, but the influence of the cavitation effect on the damping coefficient is not obvious.

Approximate Expression of Maximum Temperature of Journal Bearings Based on Simplified Thermohydrodynamic Lubrication Model

Approximate Expression of Maximum Temperature of Journal Bearings Based on Simplified Thermohydrodynamic Lubrication Model

A Thermo-hydrodynamic lubrication model of a mechanical seal modified by equivalent film thickness

An effective way to improve the combined performance of mechanical seals is to optimize their surface textures using multi-objective optimization method. For compatibility with the multi-objective optimization algorithm, the theoretical performance of a mechanical seal is often determined using the finite-difference method (FDM). However, compared with the finite-volume method (FVM) and finite-element method (FEM), FDM is weaker for dealing with the issue of discontinuous film thickness for a textured surface. In the present study, the thermo-hydrodynamic lubrication model of a mechanical seal is modified by means of an equivalent-thickness treatment, and the accuracy of the modified lubrication model is assessed by comparing its predictions for film pressure and temperature with published FVM and FEM results, showing that the equivalent-thickness lubrication model is effective for addressing the issue of discontinuous film thickness. The present work is important in that it improves the simulation accuracy of multi-objective optimization for textured mechanical seals.

Temperature distribution and heat generating/transfer mechanism of the circular bilayer porous bearing for thermo-hydrodynamic problem

Circular porous bearing is a widely used self-lubricating bearing structure but it exhibits higher temperature rise in bearing system — heat produced cannot be dissipated in time — which leads to poorer lubricating performance and makes it difficult to use in complex working conditions. We establish the thermo-hydrodynamic lubrication model of circular bilayer porous bearing in polar coordinates coupling with the fluid pressure and heat transfer equations, and reveal the fundamental origin of the heat generating and its transfer mechanism. The results indicate that the circumferential velocity is the major contributor to determine the temperature distribution, and the oil film shearing causes temperature rise of the bearing system which is gradually transferred from oil film to porous medium through the heat conduction of porous metal and the convection of fluid. Thus, the temperature in the oil film region is higher than that in the porous bearing. In the vertical direction, the temperature rises first and then decreases from the bearing bottom face to the counterpart surface, While in the radial direction, the temperature increases gradually from the inner radius to the outer radius. We find that the highest temperature of the bearing system occurs at the minimum film thickness of the external ring face in the oil film region. The numerical model is verified by comparing the experimental and numerical results, and the numerical accuracy of the lubrication performance has been improved after considering the thermal effect. Our results can be employed to control the oil film temperature and exert a better lubricating performance.

Investigations of the three-dimensional temperature field of journal bearings considering conjugate heat transfer and cavitation

PurposeThe growing demand of efficiency and economy has led to a dramatic increase of the operating speed of the journal bearing, with a higher temperature distribution. This paper aims to investigate the three-dimensional temperature distribution of journal bearings.Design/methodology/approachA thermo-hydrodynamic lubrication model of a journal bearing was established based on the full 3D CFD method. A two-sided wall was used to include the conjugate heat transfer effect. The temperature-dependent characteristics of lubrication and cavitation impact were also included. The simulation results well agreed with the experimental results. Based on this method, the three-dimensional temperature distribution was analyzed under different operating conditions.FindingsThe temperature distribution in the radial direction had a difference. An increase of speed and de-crease of inlet temperature promoted temperature differences in the higher temperature zone and the increasing temperature zone, respectively. However, the inlet pressure had less influence on these differences. The temperature distribution was basically the same at a lower bearing conductivity. As the conductivity increased, the radial temperature difference was increased.Originality/valueThe temperature distribution in the radial direction was found under different operating conditions, and the present research provides references to understand the three-dimensional temperature distribution of journal bearings.

Thermohydrodynamic Analysis of High-Speed Water-Lubricated Spiral Groove Thrust Bearing Using Cavitating Flow Model

A thermohydrodynamic lubrication model of turbulent cavitating flow for high-speed spiral groove thrust bearing was developed considering the effects of cavitation, turbulence, inertia, breakage, and coalescence of bubbles. Comparing with the classical thermohydrodynamic model, this model can predict not only the distributions of pressure and temperature rise but also the distribution of bubble volume and bubble number density. Static characteristics of the water-lubricated spiral groove thrust bearing in the state of turbulent cavitating flow were analyzed, and the influences of multiple effects on the static characteristics of the bearing were researched. The numerical calculation result shows that the bubbles are mainly distributed in inlet and outlet of the spiral groove, the distribution of bubble volume is skewed under the equilibrium state, and small bubbles account for a large proportion of the cavitating flow under high-speed condition. Furthermore, the load carrying capacity and the leakage flow of the bearing decrease due to the effect of cavitation under high-speed. The maximum temperature rise of the bearing decreases due to the effect of cavitation effect.

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.

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.