Textured Thrust Bearings Research Articles

A comparative study on turbulent models for three-dimensional thermo-hydrodynamic analysis of textured thrust bearing

A comparative study on turbulent models for three-dimensional thermo-hydrodynamic analysis of textured thrust bearing

Effects of differently shaped textures on the tribological properties of static and dynamic pressure thrust bearings and multiobjective optimization

PurposeThe purpose of this study is to evaluate three types of textures designed to enhance the tribological performance of static and dynamic pressure thrust bearings.Design/methodology/approachTo explore the effects of different types of textures on tribological performance, the Reynolds equation is modified using lubrication theory and computational fluid dynamics methods while considering the influence of cavitation and turbulence on the physical field. In addition, the tribological performance is optimized through an improved selection algorithm based on Pareto envelope (PESA).FindingsThe results indicate that textured thrust bearings exhibit superior tribological performance compared to untextured ones. The circular texture outperforms other textures in terms of load-bearing and friction performance, with improvements of approximately 28.8% and 18.9%, respectively. In addition, the triangular texture exhibits the most significant temperature improvement, with a reduction of approximately 1.93%.Originality/valueThe study proposes three types of textures and evaluates the friction performance of thrust bearings by modifying the Reynolds equation. In addition, the optimal texture design is determined using an improved selection algorithm based on PESA.

Parametric Design Optimization of Convergent Textured Thrust Bearing in THD Behaviour

Textured thrust bearing is a technological means capable of providing higher performance compared to untextured bearing. This paper presents a parametric design optimization with thermohydrodynamic (THD) behaviour of textured thrust bearing in a range of convergence ratios. The bearing consists of eight pads (stator), film fluid and a collar (rotor). The main objective of this optimization is to provide higher load capacity, to relatively minimize the maximum temperature of the pad and the friction torque. To this aim, we perform a 3D computational fluid dynamics model for convergent thrust bearing with individual angular sector shaped texturing with a flat bottom profile pad, by using ANSYS. CFX, and considered a thermal effect.

Texture Optimization and Verification for the Thrust Bearing Used in Rotary Compressors Based on a Transient Tribo-Dynamics Model

Abstract Rotary compressors are designed more and more compact, and the compressor cylinder’s ambient pressure is designed very high to facilitate oil separation and improve efficiency. However, these designs cause the working condition of the thrust bearing becoming harsher, and severe wear may occur. The present study is aimed at mitigating its wear condition through surface texturing. Based on a transient tribo-dynamics model considering the coupling effect of the journal and thrust bearings, a texture optimization study for the thrust bearing is conducted, in which three different stochastic optimization algorithms are utilized. The results show that thrust bearings with optimized textures have significantly reduced contact forces and wear under a high working frequency due to an extra hydrodynamic support around the texture dimples. The optimized texture designs are fabricated on the thrust bearing surfaces by a high-accurate picosecond laser machine, and their performance is assessed through experiments using a compressor performance test platform. The experiment results confirm that the textured thrust bearing has a lower wear depth. Moreover, the coefficient of performance (COP) of the testing compressor with textured thrust bearing is increased while its input power decreases, which implies a reduced friction force and a higher energy efficiency.

Inertial contributions to friction measurements in thrust bearings

Surface textures decrease friction in lubricated sliding contact. Traditionally, the friction reduction for a given textured surface is determined by using the Reynolds equation, which neglects fluid inertia. However, as the separation and relative motion between the surfaces increase, inertia can affect the measured tangential and normal forces for flow over a textured surface, and thus cause the coefficient of friction to differ from the purely viscous, Stokes flow prediction. Here, the increase in torque and normal force between a moving plate and stationary textured surface, which simulates a textured thrust bearing, are calculated as a function of the Reynolds number in the thin film limit. The predictions for a non-textured thrust bearing are compared to fully 3-D numerical simulations of the incompressible Navier-Stokes equation, and the predictions for textured thrust bearings are compared to experimental data given in the literature. Good agreement is seen between the predictions and the data, validating the predicted scaling laws. This work also suggests that inertia can be used as a secondary effect to reduce friction in lubricated sliding, and textures that take advantage of the inertial effects will have lower friction than textures that only use purely viscous effects.

Tribological analysis of picosecond laser partially textured thrust bearings with circular grooves machined: Theory and experiment

A two-dimensional analytical model based on the Reynolds equation considering mass conservation cavitation is proposed to investigate the performance of partially textured thrust bearings with circular grooves. The geometrical and distribution parameters of the circular grooves are numerically optimized to obtain the maximum load-carrying capacity. The samples of partially textured thrust bearings are machined by the picosecond laser, and tribological experiments are carried out on an MMW-1 tribological rig. The average friction coefficient and the friction reduction ratio are applied to analyze the tribological performance of partially textured thrust bearings. Through a comparative analysis, the optimal geometrical values obtained from the experimental results are in good agreement with the theoretical analysis, especially at high rotation speeds and a low load condition.

Effects of thermal and mechanical deformations on textured thrust bearings optimally designed by a THD calculation method

A performance optimisation study of a thrust bearing with surface texturing has been addressed. Bearing response calculations have been performed with a thermohydrodynamic modelling approach. A THD-optimal bearing design has been calculated, and a sensitivity analysis has been performed. The optimal design has been evaluated utilising a thermoelastohydrodynamic model, in order to quantify the effects of thermal deformations on tribological characteristics, and a sensitivity analysis demonstrated a small difference on the parameter set of the optimal geometry. However, bearing performance is substantially affected by thermal deformations, leading to a reduction of thrust load by 13% and an increase of friction coefficient by 10%. The presented results highlight the importance of modelling thermal deformation on the design of textured thrust bearings.

Investigation and optimization of textured thrust bearings with spirally distributed dimples using multi-objective optimization method

Purpose Surface textures have been widely used in thrust bearings as a means of enhancing the tribological performance. The effect of textures with a spiral distribution on the lubrication characteristics of thrust bearings has not been fully covered. This paper aims to investigate and find the optimal structure and distribution parameters of textures with the maximum loading capacity and minimum friction force as goals. Design/methodology/approach Combining the multi-objective optimization method based on the non-dominated sorted genetic algorithm-II with response surface methodology, the key textured parameters are optimized. Local sensitivity analysis is used to evaluate the impact level of each parameter. Findings Spiral distribution of textures can effectively improve the lubrication performance of the thrust bearing compared with the linear distribution. The distribution with high amplitudes and high cycle numbers will weaken the spiral effect and destroy the high-pressure region. Through the multi-objective optimization of the textured structure and distribution parameters, the loading capacity demonstrates a 55.05per cent improvement compared to the basic model. Textured width is the most sensitive parameter for both loading capacity and friction force. Originality/value Present research provides a fundamental design guide for textured thrust bearings.

The Influence of Surface Patterning on the Thermal Properties of Textured Thrust Bearings

Contact performance can be enhanced by using textured surfaces. These are also found to have influences on lubricated contacts. A procedure to find the optimal partially textured thrust bearing configuration is presented in this study. A parallel sector-pad thrust bearing is simulated by a three-dimensional (3D) computational fluid dynamics (CFD) model. The stationary surface of the bearing is textured with dimples, while the rotor surface is flat. The results of the baseline model are validated by experimental data. In this study, we compare rectangular and elliptical dimples by investigating design parameters, such as major the length of the major axis (width), the length of the minor axis (length), dimple depth, circumferential space between two dimples, radial space between two dimples, radial extent, circumferential extent are selected as design parameters. A parametric study is conducted to investigate the influence of the texture geometries and a surrogate model is created. Based on the surrogate model, a multi-objective optimization scheme is used to navigate the design space and find the optimal texture structure that provides a lower maximal temperature inside the fluid film, higher load capacity, and lower friction torque. The results show that the optimal radial extent of the texture is around 80% of the pad radial length for both cases. The optimal length of the elliptical dimples in the circumferential direction is about 30% larger than the value of the rectangular dimples. In the final optimal design, the maximal temperature reduces 1.1% and 1.3% for rectangular and elliptical dimples while the load capacities are maintained at the same level.

Investigation on inner flow field characteristics of groove textures in fully lubricated thrust bearings

PurposeThe purpose of this study is to investigate the inner flow field characteristics of groove textures in thrust bearings. Cavitation and vortex are studied simultaneously to enrich the theories of surface texture.Design/methodology/approachNavier–Stokes equations are solved using computational fluid dynamics. The MIXTURE model is adopted to study the gas–liquid mixture flow under the cavitation condition.FindingsRe number, the depth ratio as well as the area ratio of the groove texture and the bottom shape are all influencing factors of the inner flow field characteristics. When cavitation region and vortex region occupy the bottom of the groove texture, these do not overlap because of the pressure gradient. The positive pressure gradient in the non-cavitation region introduces nonlinearity into the velocity profiles, which affects the load-carrying capacity and friction.Originality/valueCavitation and vortex are studied simultaneously only in this study. The characteristics of the textured thrust bearing can be analyzed and explained with the combined effect of cavitation and vortex.

Experimental analysis of the hydrodynamic effect during start-up of fixed geometry thrust bearings

Abstract Most of the investigations on thrust bearings were performed under a steady-state condition and this regime is now well understood. Contrary to this, the behavior during the first period of start-up is sparsely studied. Start-ups of thrust bearings are critical periods where a mixed lubrication regime occurs. This regime can be detrimental for the lifetime of the system. It is usually mentioned in the literature that the textures act as micro reservoirs which can be beneficial to help lift-up during start-up. This is an intuitive hypothesis and there are no experimental results to prove it. This study uses an experimental approach in order to analyze the behavior of different kinds of thrust bearings with fixed geometry. It mainly focuses on the capability of textured thrust bearings to lift up during start-up. This study shows that only specific texture geometry can help the formation of a fluid film. The results are compared to those obtained with classical geometries like tapered land, pocketed and untextured flat-land thrust bearings. The original results show a relatively good ability of flat-land thrust bearings to generate a lift-up during the start-up period. An experimental device is used to measure, at high frequency, the friction torque as well as the electrical resistance across the fluid film to determine the lubrication regime. The comparative analysis allows us to explain the factors which modify the contact.

An Optimum Design Approach for Textured Thrust Bearing With Elliptical-Shape Dimples Using Computational Fluid Dynamics and Design of Experiments Including Cavitation

Textured thrust bearings are capable of providing higher load capacity and lower friction torque compared to nontextured bearings. However, most previous optimization efforts for texturing geometry were focused on rectangular dimples and employed Reynolds equation. Limited studies have been done to investigate the effects of partially textured thrust bearings with elliptical dimples. This study proposes a new optimization approach to find the optimal partially texture geometry with elliptical dimples, which maximize the loading capacity and minimize the friction torque. In this study, a 3D computational fluid dynamics (CFD) model for a parallel sector-pad thrust bearing is built using ANSYS cfx. Mass conserving cavitation model is used to simulate the cavitation regions. Energy equation for Newtonian flow is also solved. The results of the model are validated by the experimental data from the literature. Based on this model, the flow pattern and pressure distribution inside the dimples are analyzed. The geometry of elliptical dimple is parameterized and analyzed using design of experiments (DOE). The selected geometry parameters include the length of major and minor axes, dimple depth, radial and circumferential space between two dimples, and the radial and circumferential extend. A multi-objective optimization scheme is used to find the optimal texture structure with the load force and friction torque set as objective functions. The results show that the shape of dimples has a crucial effect on the performance of the textured thrust bearings. Searching the design space for a proper combination among the design variables satisfying the constraints has the advantage of capturing the codependence among design variables and leads to a surface patterning of the bearing, which showed a 42.7% improvement on the load capacity.

Experimental Study on Transient Behavior of Cavitation Phenomenon in Textured Thrust Bearings

The transient behavior of cavitation phenomenon in textured thrust bearings with oil lubricant was experimentally investigated. During experiments, the cavitation phenomenon in different surface textures was observed directly with a high-speed camera. It is shown that cavitation shape and area change according to texture patterns. The bubbles within cavitation zones increase with running time in the beginning and gradually reach a steady state, meaning that a transient period is needed to achieve equilibrium. In addition, the bubble composition was analyzed under the temperature of 35 °C and pressure of 30 kPa. The results show that oil vaporization plays a minor role in the formation of bubbles.

Performance of Hydrostatic Textured Thrust Bearing with Supply Holes Operating with Non-Newtonian Lubricant

ABSTRACTThe present article proposes a technique to improve the performance of textured hydrostatic thrust bearings with the use of oil supply holes. The article provides a comparison between smooth and surface-textured hydrostatic thrust bearings. To get an accurate prediction of the caviation regime, the Jakobsson-Floberg-Olsson (JFO) mass conservation algorithm has been used instead of the Reynolds boundary conditions. It has been observed that surface texture results in a significant decrease in friction power loss along with an improvement in other performance parameters. The study also reveals that the location of the supply hole for the lubricant system significantly affects the bearing performance.

Performance Comparison of Partial and Full Textured Thrust Bearing Operating with Non-Newtonian Lubricant

The present paper theoretically investigates the influence of partial and full texture on the performance of the hybrid thrust pad bearing operating with non-Newtonian lubricant. The presented results show that the dilatant lubricant with partial textured surface has the maximum load carrying capacity. The effect of full texture on hybrid thrust bearing is positive. In the present paper, Finite element method with Reynolds boundary conditions is implemented. The comparative study shows that partial texturing in the bearing significantly works better than the full texturing and the friction coefficient in the bearing can be reduce upto 60% as shown in the results.

An experimental analysis of the hydrodynamic contribution of textured thrust bearings during steady-state operation: A comparison with the untextured parallel surface configuration

Textured surfaces are the subject of a great deal of research work in tribology, which mainly involves numerical studies of lubricated contacts. A variety of shapes and arrangements of textures can be found, these being as numerous as the different authors. Depending on the configuration, it has been shown that the presence of the texture can provide better lubrication efficiency through both a reduction of friction and an increase in load-carrying capacity. However, improving bearing performance implies a specific geometrical configuration for given operating conditions. The improvement in lubricated contact performance by texturing the active surface has been demonstrated using experimental studies concerning, for example, pin-on-disk, mechanical seal, camshaft, journal bearing, thrust bearing, and piston ring set-ups. The objective of the present experimental analysis is to provide, using local measurements, a better understanding of the influence of surface texturing on the steady-state behavior of thrust bearings. To achieve this goal, the experimental device is equipped with 80 sensors such as thermocouples and pressure transducers which allowed a proper assessment of the phenomenology at the film/pad interface. The tests are conducted on five hydrodynamic thrust bearings, among which four are textured. Results show that, for the studied configurations, the textured thrust bearings can help to reduce friction up to 30% at low loads while for heavy loads, their performance is equivalent or even lower than that of an untextured planar bearing.

Characterization of Stiffness and Damping in Textured Sector Pad Micro Thrust Bearings Using Computational Fluid Dynamics

In the present paper, a study of stiffness and damping in sector-pad micro thrust bearings with artificial surface texturing is presented, based on computational fluid dynamics (CFD) simulations. The bearing pads are modeled as consecutive three-dimensional independent microchannels, each consisting of a smooth rotating wall (rotor) and a partially textured stationary wall (stator). CFD simulations are performed, consisting in the numerical solution of the Navier–Stokes equations for incompressible isothermal flow. The goal of the present study is to characterize the dynamic behavior of favorable designs, identified in previous optimization studies, comprising parallel and convergent thrust bearings with rectangular texture patterns. To this end, a translational degree of freedom (DOF) along the thrust direction and a rotational (tilting) DOF of the rotor are considered. By implementing appropriate small perturbations around the equilibrium (steady-state) position and processing the simulation results, the stiffness and damping coefficients of the bearing are obtained for each DOF. The computed dynamic coefficients of textured thrust bearings are compared to those of conventional (smooth slider) designs. It is found that the dependence of bearing stiffness and damping on geometrical parameters exhibits the same trends for both DOFs. Both stiffness and damping are found to increase with bearing width. In general, increasing the bearing convergence ratio results in increased bearing stiffness and decreased damping. Finally, the present results demonstrate that properly textured parallel sliders are characterized by an overall dynamic performance that is superior to that of smooth converging sliders.

Theoretical and Experimental Analysis of a Laser Textured Thrust Bearing

In this article, a laser partially textured thrust bearing is theoretically and experimentally analyzed. An adiabatic model is developed in order to theoretically investigate the performances of the bearing. The bearing sample is partially textured both in radial and circumferential direction using the laser texturing process. The performance of the bearing (fluid film thickness and friction torque) is evaluated on a specially adapted test rig and the experimental results are compared with the theoretical model. A good agreement is found between the theoretical model and the experimental data. Also a comparison between a laser textured bearing and a bearing textured using the photolithographic method is presented.