Computational Fluid Dynamics Thermohydrodynamic Analysis of Three-Dimensional Sector-Pad Thrust Bearings With Rectangular Dimples

The paper presents a detailed computational study of flow patterns and performance indices in a dimpled parallel thrust bearing. The bearing consists of eight pads; the stator surface of each pad is partially textured with rectangular dimples, aiming at maximizing the load carrying capacity. The bearing tribological performance is characterized by means of Computational Fluid Dynamics (CFD) simulations, based on the numerical solution of the Navier-Stokes and energy equations for incompressible flow. Realistic boundary conditions are implemented. The effects of operating conditions and texture design are studied for the case of isothermal flow. First, for a reference texture pattern, the effects of varying operating conditions, in particular minimum film thickness (thrust load), rotational speed and feeding oil pressure are investigated. Next, the effects of varying texture geometry characteristics, in particular texture zone circumferential/radial extent, dimple depth and texture density on the bearing performance indices (load carrying capacity, friction torque and friction coefficient) are studied, for a representative operating point. For the reference texture design, the effects of varying operating conditions are further investigated, by also taking into account thermal effects. In particular, adiabatic conditions and conjugate heat transfer at the bearing pad are considered. The results of the present study indicate that parallel thrust bearings textured by proper rectangular dimples are characterized by substantial load carrying capacity levels. Thermal effects may significantly reduce load capacity, especially in the range of high speeds and high loads. Based on the present results, favorable texture designs can be assessed.

This paper investigates the effects of imperfect texture shape and dimensional uncertainty on the surface texture performance (load-carrying capacity and coefficient of friction) by adopting numerical experiments, statistical models, and artificial neural network. The imperfect texture shape is regarded as a polygon, and the uncertain geometrical dimensions include the dimple diameter, the area density, and the dimple depth. Results reveal that the most critical geometric parameters that influence the friction force are manufacturing errors associated with the texture’s area density. With respect to the load-carrying capacity and the coefficient of friction, manufacturing errors associated with the dimple diameter are more influential than those of the dimple depth and the area density. It is shown that insofar as the optimization of surface texture performance is concerned, the imperfect texture shape and the dimensional uncertainty associated with the laser texturing with three-sigma performance level are harmless, but manufacturing errors with the one-sigma level can dramatically reduce the load-carrying capacity and increase the coefficient of friction. Specifically, when the dimensions of the area density, the dimple depth, and the dimple diameter are set as 30%, $5.5~\mu \text{m}$ , and $100~\mu \text{m}$ , respectively, the imperfect texture shape at the three-sigma level can achieve higher performance than lower levels of control of machining precision.

In this study, the effects of three types of dimples with different internal structures on the fluid lubrication characteristics of seal-like thrust bearings were experimentally and numerically investigated. In the experiments, the load-carrying capacity and the frictional torque were measured. The measurements were performed with a fixed constant film thickness. The behaviors of cavitation bubbles occurred within the dimples were observed through the rotating glass plate. Three types of internal structures of dimples were tested: cylindrical, spherical and conical. The measurement results were simulated by using the Reynolds equation. In addition, applying the periodic condition, a single dimple was analyzed. As the results, in three types of dimples, the load-carrying capacity increased as the rotational speed increased. The cylindrical internal structure built up the largest pressure at the trailing edge of dimples, and consequently the largest load-carrying capacity. The frictional torque also increased with increasing the rotational speed in the dimpled bearings. However, the effect of the internal structure on the frictional torque was not significant. Analytical results showed that the pressure reached the maximum value at the trailing edge of the cylindrical internal structure. The conical and sphere internal structure had the maximum value slightly inside the trailing edge.

Shape optimization of hydrodynamic textured surfaces for enhancing load-carrying capacity based on level set method

Double-row tapered roller bearings (DTRBs) are key components of rotating machineries due to its great advantages in load-carrying and stiffness. Friction torque is one of the major indicators used to evaluate the performance of rolling bearing because it directly related to the power loss and heat generation. Nevertheless, the friction torque of DTRB is not deeply studied in the available literatures, especially those consider the influence of angular misalignment and radial clearance. Therefore, in current paper, the friction torque of DTRB is thoroughly investigated under combined radial and thrust load according to the extended mechanical model of DTRB. The total friction torque is considered as the summation of EHL rolling friction torque, elastic hysteresis loss, sliding friction at rib-roller end contact and viscous drag friction of lubricant. The current work mainly considers the influences of three parameters: axial pre-deformation, initial radial clearance and angular misalignment on the friction torque of the first and the second row of DTRB. The results indicate that the friction torque of these two rows of DTRB are greatly determined by the above parameters. Regardless the first or the second row, friction torques are both increase with the increase of axial pre-deformation and positive/negative angular misalignment, while decrease with the increase of initial radial clearance. The analysis of friction torque for DTRB will provide some useful guidance for the applications of DTRB.

Squeeze film investigations focus upon film pressure, load bearing quantity and the minimum thickness of film. The combined effect of pressure viscous dependent and non- Newtonian couple stress in porous annular plate is studied. The modified equations of one dimensional pressure, load bearing quantity, non dimensional squeeze time are obtained. The conclusions obtained in the study are found to be in very good agreement compared to the previous results which are published. The load carrying capacity is increased due to the variation in the pressure dependent viscosity and also due to the couple stress effect. Finally this results in change in the squeeze film timings.

PurposeCompression rings are the main sources of frictional losses in internal combustion engines. The present paper aims to present a thermo-mixed hydrodynamic analysis for coated top compression rings. To understand the coating effects, the main tribological parameters are investigated into a ring-cylinder conjunction in a motorbike engine. Furthermore, flow simulations have been carried out on how different worn profiles on the cylinder inner liner affects friction, lubricant film and localized contact deformation of the coated compression rings.Design/methodology/approachIn this paper, the basic geometrical dimensions of the top compression ring-cylinder system are obtained from a real motorbike engine. A 2D axisymmetric CFD/FLOTRAN model is created for coated compression rings. Flow simulations are performed by solving the Navier-Stokes and the energy equations. The load capacity of the asperities is also taken into account by Greenwood and Tripp contact model. Realistic boundary conditions are imposed to simulate the in-plane ring motion. The simulation model is validated with analytical and experimental data from the literature. Under thermal considerations, the contribution of worn cylinder profiles in conjunction with different coated compression rings is presented.FindingsThis research shows that because of thermal effects, the boundary friction is higher at reversals and the viscous friction is lower because of reduced oil viscosity. As regards to the isothermal case, the viscous friction is greater because of a higher lubricant viscosity. In the case of chromium-plated ring, boundary friction was 16 per cent lower than a grey cast iron ring taking into account thermal effects. Regarding the localized contact deformation, the coated compression rings showed lower values under different worn cylinder shapes. In particular, hard wear-resistant (Ni-Cr-Mo) coating showed the slighter local deformation. Therefore, the worn cylinder profiles promote boundary/mixed lubrication regime, whereas the lobed profile of cylinder inner liner becomes more wavy.Originality/valueThe solution of the thermo-mixed lubrication model, concerning the piston ring and worn cylinder tribo pair by taking into account the coating of the top compression ring.

The hydrodynamic herringbone groove journal bearing (HGJB) performs exceptionally well at high speeds but is limited by a low load-carrying capacity, largely due to the lubrication characteristics of water. To address this issue, a hybrid water-lubricated HGJB is proposed in this study. A lubrication model for the high-speed hybrid water-lubricated HGJB is developed, taking into account turbulence, thermal effects, and tilt. A comparative analysis of the static characteristics is conducted between the hybrid HGJB and both the hydrodynamic HGJB and the hybrid plain journal bearing (PJB). The results show that the proposed hybrid water-lubricated HGJB offers significantly greater load-carrying capacity than the conventional hydrodynamic HGJB, particularly during start-up or at low speeds. For example, when the bearing operates at 1000 rpm with an eccentricity ratio of 0.5, the load-carrying capacity of the water-lubricated hybrid HGJB under a supply pressure of 1.6 MPa reaches 650 N, compared to just 261 N for the water-lubricated hydrodynamic HGJB. Additionally, the hybrid water-lubricated HGJB demonstrates a higher flowrate and lower temperature rise than the traditional hybrid PJB, thanks to the improved pumping effect of the herringbone grooves at high speeds.

Purpose The stringent requirements for environmental protection have induced the extensive applications of water-lubricated journal bearings in marine propulsion. The nonlinear dynamic analysis of multiple grooved water-lubricated bearings (MGWJBs) has not been fully covered so far in the literature. This study aims to conduct the nonlinear dynamic analysis of the instability for MGWJBs. Design/methodology/approach An attenuation rate interpolation method is proposed for the determination of the critical instability speed. Based on a structured mesh movement algorithm, the transient hydrodynamic force model of MGWJBs is set up. Furthermore, the parameters’ analysis of nonlinear instability for MGWJBs is conducted. The minimum water film thickness, side leakage, friction torque and power loss of friction are fully analyzed. Findings With the increase of speed, the journal orbits come across the steady state equilibrium motion, sub-harmonic motion and limit circle motion successively. At the limit circle motion stage, the orbits are much larger than that of steady state equilibrium and sub-harmonic motion. The critical instability speed increases when the spiral angle decreases or the groove angle increases. The minimum water film thickness peak is at the rotor speed of 4,000 r/min for the MGWJB with Sa = 0°. As rotor speed increases, the side leakage decreases slightly while the friction torque and the power loss of friction increase gradually. Originality/value Present research provides a beneficial reference for the dynamic mechanism analysis and design of MGWJBs.

Gas foil journal bearings (GFJBs) are critical components in high-speed turbomachinery due to their advantages such as increased load capacity, reduced friction, and improved rotordynamic stability. This study presents a comprehensive numerical analysis comparing the static and dynamic performance of herringbone groove textures—namely single, double, and multi-structured patterns—applied to the top foil of GFJBs. The pressure distribution is obtained by solving the Reynolds equation using the finite difference method, and key performance metrics such as load-carrying capacity, frictional torque, power loss, effective stiffness, damping, and system stability are systematically evaluated. Among the patterns, the multi-herringbone texture (Texture 3) consistently outperformed other configurations. To further enhance performance, a multi-objective Particle Swarm Optimization (PSO) algorithm was employed to optimize key groove parameters. The optimized configuration yielded improved static and dynamic behavior, including higher stiffness and damping values and enhanced system stability. Notably, the optimized textured GFJB demonstrated a 26.9% increase in load-carrying capacity (LCC) compared to the plain GFJB. This research highlights the effectiveness of surface textures in enhancing GFJB performance and demonstrates the utility of PSO as a powerful tool for multi-objective optimization in high-speed bearing design.

All propeller-driven ships employ a drive shaft supported by journal bearings. To avoid water pollution, these bearings are generally lubricated by the surrounding water, removing the need for a rear seal. Such bearings, commonly referred to as Cutlass bearings, usually have an inner grooved nitrile rubber lining. The grooves (called flutes) allow debris to be flushed out and the bearing surface to be cooled. The remaining area is divided into a number of load-carrying areas called staves. At present, no rigorous design guide exists for these bearings. This paper presents a methodology to predict the minimum film thickness between the journal and the most heavily-loaded stave, an approach not hitherto reported in the literature. The method includes a new, 3D, finite element (FE) approach for soft elasto-hydrodynamic (EHL) predictive modelling of generated pressures in cutlass bearings. Model predictions compare favourably with experimental data. It is shown that the modulus of elasticity of the rubber has no influence on the minimum film thickness. An equation relating dimensionless film thickness to dimensionless load, clearance ratio and numbers of staves is presented. For a nominally circular bearing, increasing the clearance ratio or increasing the numbers of staves reduces load-carrying capacity. It is shown that distortion due to loading can increase load-carrying capacity.

The theory of the lubrication of plane sliders of finite width-thrust block bearings-has been developed by a method that is more convenient for numerical calculations than that of Michell and Boswall. Whereas previously all the derived properties of such systems have had to be obtained by direct graphical and numerical procedures, explicit analytical expressions have been obtained in the present theory for the friction coefficients, the inclination of the wedges, the load-carrying capacities, the minimum film thickness, and the lubricant flow. The theory has been applied numerically to a much wider range of conditions than has been done before. In particular, with respect to self-aligning thrust bearings or sliders, numerical results have been obtained so as to cover both the range where the pivot is very near the center of the slider and where it is set within short distances of the trailing edge. With such extended ranges it has been possible to construct complete curves for the variation of the important derived properties of the slider system as functions of the pivot position.

Comparison of Exact and Sommerfeld Solution for the Pressure of a Journal Bearing

Controlling friction and wear are essential for reducing energy loss and lengthening the life span of friction pairs in sliding contacts. Surface texturing is an effective and efficient way to reduce friction and wear, especially under lubricated conditions. Dimple texture on friction pair surfaces has been verified to enhance the lubrication condition and shift the lubrication regime by generating additional hydrodynamic pressure. However, the geometric features and distribution of the microstructures considerably influence the production of additional pressure. Choosing and designing dimple texture with suitable geometric features is necessary and important for texturing applications. In this study, computational fluid dynamics (CFD) are used to investigate the effect of the geometric features of dimple textures on pressure build-up. The influence of dimple shapes, dimple depths, minimum film thickness, dimple densities, and dimple surface angles are presented and discussed. Notably, the influence of the dimple surface angle is introduced and presented.

A mass-conservative algorithm that implements the Jakobsson–Floberg–Olsson cavitation theory is used to predict the performances of seal-like structures and thrust bearings with a dimpled surface texture. The results of a series of simulations for load-carrying capacity, film thickness, dimple depth, dimple density, cavitation pressure, leakage, and friction force are presented, and the relationship between these performance parameters is studied. It is shown that, under the conditions simulated, surface roughness can improve the load-carrying capacity, but its effect is limited.