non-Newtonian Lubricant Research Articles

On the Study of Impact Plasto-Elastohydrodynamic Lubrication of Point Contact Problems Lubricated With Non-Newtonian Lubricant

Abstract In this study, the impact of a rigid ball on a substrate with lubricant in between is examined. A linear hardening model for the elastic/plastic substrate deformation is assumed. A power-law model is used to describe the lubricant rheology. Throughout the impact period, variations in the pressure distribution, the film thickness distribution, the velocity of a rigid ball, the impact load, the von Mises stress distribution, and the plastic strain distribution on the substrate are calculated. The special cases of ET = E in the present impact plasto-elastohydrodynamic lubrication (PEHL) results are in good agreement with previous impact elastohydrodynamic lubrication (EHL) results using a power-law model. The variation of central pressure over time in the PEHL model is flatter and lower compared to that in the EHL model. The significant difference shows that the plastic deformation mechanism should be considered in the simulation. The results indicate that as the flow index (n) increases, the central pressure and central film thickness increase, the pressure spike occurs earlier, and the rigid ball's rebounding velocity and maximum impact load decrease. Moreover, as the tangent modulus of the linear hardening model of the substrate increases, the rigid ball's rebounding velocity and the maximum impact load increase, and the substrate deformation and plastic strain decrease.

Study of MHD on porous flat and curved circular plate lubricated with couple stress fluid-a slip velocity model

The current study achieved to explore novel of curved circular and porous flat plate under the existence of MHD and slip velocity. The gap between the plates is filled with conducting non-Newtonian lubricant as a couple stress fluids. We considered the phenomena of Darcy law is account for porous medium and Stokes theory is used to incorporate to couple stress effects. The effect of MHD slip velocity and couple stress lubricant is studied. By taking into account the couple stresses due to the microstructure additives and the magnetic effects due to the magnetization of the magnetic fluid modified Reynolds equation is obtained. The Reynolds equation is solved we obtain the derivation of non-dimensional pressure distribution, load carrying capacity and squeeze film time. Employing the Simpsons 1/3rd rule for numerical analysis in Mathematica tool and Origin Software to illustrate the behavior of pressure profile, load carrying capacity and squeeze film time in effect of Harmann number, couple stress parameter, slip velocity and permeability parameter. The results indicate that the influence of couple stresses and magnetic effects on the bearing characteristics are significantly apparent. It is concluded that fluids with couple stresses are better than Newtonian fluids. The improvement of the bearing characteristics is enhanced if the magnetic effects and slip velocity are present. But reverse effect due to upsurge of permeability parameter.

New mathematical models for the load factor of slip pairs of the ship propulsion complex for non-Newtonian lubricants

The method of boundary variation was applied to the solution of the boundary value problem with respect to the Reynolds differential equation for the lubricating layer in the sliding bearings of ship power plants and auxiliary ship equipment, which made it possible to obtain analytical representations for the hydrodynamic pressure, shear stresses, as well as the integral characteristics of the lubricating layer. This made it possible to build new, easy-to-use mathematical models for the load factor (carrying force factor) of the sliding pairs of the ship propulsion complex, considering the non-Newtonian properties of lubricants, i.e. in the case of the dependence of dynamic viscosity on pressure and temperature. Mathematical models take into account geometric parameters of bearings, operational parameters: relative radial clearance and relative eccentricity, angular velocity; as well as viscosity characteristics of lubricants, in particular, dynamic viscosity and piezo coefficient of viscosity of lubricants. A criterion for the applicability of lubricants for given operating characteristics and bearing parameters has been developed, which uses the viscosity characteristics of lubricants. The research results are illustrated in the form of tables and graphs.

Effects of confinement-induced non-Newtonian lubrication forces on the rheology of a dense suspension

In this work, we propose a functionalised bi-viscous lubrication model to study the material properties of concentrated non-Brownian suspensions and explore the possible confinement-induced non-Newtonian effects of the lubricant in the rheological response of this type of suspensions. From tribological studies, it is well-known that even macroscopically Newtonian liquids under strong confinement might exhibit properties which deviate significantly from their bulk behaviour. When two surfaces separated by an extremely small gap (still large compared to the molecular size) are sheared, strong shear-thinning of the lubricant viscosity at low shear-rates is observed, in spite of its Newtonian-like bulk response. This is connected to a significant increase of the zero-shear-rate viscosity under extreme confinement. We start from an effective lubrication algorithm recently proposed and develop a new gap-size-dependent interparticle bi-viscous lubrication model, able to capture qualitatively the main phenomenology of confined lubricants. We solve the lubrication interaction between particles iteratively via a semi-implicit splitting scheme. Since the handling of lubrication is made implicitly here, the method copes efficiently with large increases of the inter-particle effective viscosities, which would otherwise lead to simulation blow-up or the use of vanishing time-steps in standard explicit schemes. We analyse the rheological response of the suspension systematically in terms of model parameters. In contrast to pure Newtonian lubrication interactions, distinct shear-thinning and shear-thickening regimes in the relative suspension viscosity are observed, which are discussed in terms of particle microstructure coupled with the complex rheology of the confined lubricant. In addition, normal-stress response is negative in both N1 and N2, which is difficult to achieve with standard contact frictional models.

Hydrodynamic drag reduction in ribbed microchannel with infused non-Newtonian lubricants

Liquid-infused surfaces have recently gained prominence in engineering applications owing to their versatile characteristics such as self-cleaning, anti-fogging, drag reduction, and enhanced heat transfer. In this article, a numerical analysis of pressure-driven flow past a periodic array of rectangular transverse grooves infused with non-Newtonian immiscible lubricants is performed. The volume of fluid method is employed to capture the interface between primary and secondary fluids, and the power-law model is deployed to mimic the non-Newtonian lubricant. The drag reduction capability of the microchannel is examined for various parameters such as Reynolds number, liquid fraction, viscosity ratio, viscosity index, and contact angle. It is observed that the introduction of a non-Newtonian fluid (shear-thickening or shear-thinning) drastically modifies the interface velocity and hydrodynamic resistance. In particular, a shear-thinning lubricant enhances the slip length as the viscosity index (n) is reduced owing to the reduced viscosity at the interface. Note that, for a lubricant having n = 0.7, the percentage improvement in the slip length is 382% in comparison with a Newtonian counterpart having the same viscosity ratio, N = 0.1. Importantly, the introduction of a shear-thinning lubricant with a viscosity ratio N = 5, a liquid fraction of 0.8, and a behavior index n = 0.7 yielded a pressure drag reduction of 63.6% with respect to a classical no-slip channel and of 23% with reference to a microchannel with the Newtonian lubricant. Moreover, at high Reynolds numbers, Re→50, the drag mitigation is slightly lowered due to the primary vortex shift in the cavity. Furthermore, the effect of the interface contact angle (θc) is investigated, as θc drops from 90° (flat) to 45° (convex); the meniscus curvature is enhanced, and the effective slip length is reduced. These observations suggest that a shear-thinning lubricant-infused microchannel is a promising candidate for drag reduction in lab-on-chip applications.

A novel numerical analysis method for predicting non-Newtonian lubricant (grease) distribution in ball bearings

Grease is a visco-elastic fluid and the most common lubricant for rolling bearings. During the churning phase (initial phase) of bearing operation, most of the grease is collected at various locations in the bearing, e.g. by the seal, at the bottom cage bar, in the cage pockets, which are then called grease reservoirs. These are formed based on bearing operating conditions, grease type, bearing geometry, bearing type. The grease reservoirs supply lubricant to the bearing contacts via bleeding: during operation the oil bleeds out of the reservoirs and lubricates the contacts. Since the distribution of grease is crucial to the bearing lubrication, the design of bearing components e.g., the cage, shall aim at an optimal grease reservoir creation during the churning phase. It is difficult to observe the effect of component design on the grease distribution through real life experiments, so CFD simulations with MPS (Moving Particle Semi-implicit) method are performed here. Flow Simulations with MPS method can help determine the factors influencing the grease distribution inside the bearing after churning, with the final aim of enhancing lubrication. For the current simulations, a CAE software based on MPS, namely Particleworks, was used. Grease consists of a base oil, a thickener, and additives. Since it is a non-Newtonian fluid, it has a nonlinear relation shear stress vs shear rate. It is a visco-elastic material, so it does not flow in the absence of a threshold force. For current simulations, the grease rheology has been modelled using the Herschel-Bulkley model. The model was fitted on in-house rheometer test data and was reduced to a single cage-ball segment. All critical kinematic properties were preserved, that is the speeds of both the inner ring and ball surfaces and the oscillation of the ball position within the pocket as it travels through the loaded and unloaded zones of the bearing. The location and the duration of grease injections resulted in different grease distributions in the model. For demonstration purposes, this document only focuses on the results obtained injecting a grease layer on the inner ring surface in front of the contact. This realistically predicted grease reservoirs to be located at the cage bottom, on the top of cage and in the cage pockets. Sensitivity study on particle size, time step, surface tension and the parametric variation of the bearing speed were also performed. This is an important milestone, as we are able for the first time to virtually simulate the onset of grease reservoirs at locations corresponding to evidence from real bearing operations. The distribution of grease observed at the cage pockets is very important for oil film replenishment. This outcome gives us confidence that the MPS method can be used to support the design of bearing components contributing to enhanced lubrication.

In-situ ultrasonic viscometry of lubricants under temperature and shear

Understanding the behaviour of engine and gear oils, especially the viscosity, under temperature and shear is important to improve machine operation. A novel viscometer using ultrasound is presented and used under a range of temperatures. A single cross-temperature (between 20°C and 60°C) ultrasonic calibration is shown to be sufficient. Next, the ultrasonic viscometer is compared to a conventional viscosity measurement technique for Newtonian and non-Newtonian lubricants. Newtonian viscosity standard fluids and shear-thinning engine oils are studied. Both viscosity measurement techniques match for Newtonian fluids but ultrasonic measurements are consistently lower for shear-thinning fluids. It suggests that the ultrasonic viscometer is similar to a high-shear viscometer with a shear rate of about 106s−1.

Numerical analysis of finite bearing operating under non-Newtonian lubricant and flow turbulence effect

The purpose of this work is to evaluate the combined influence of turbulence and shear-thinning/shear-thickening lubricant on the steady-state characteristics of hydrodynamic journal bearings. The modified Navier–Stokes equation for linear turbulence and non-Newtonian (shear-thinning as well as shear-thickening aspect) lubricants are solved using a finite element method to acquire load capacity, attitude angle, friction coefficient variable, total oil flow, and temperature rise variable for distinct combined values of the flow behavior index and Reynolds number. This work utilizes the Navier–Stokes equation with Ng–Pan's linear turbulence and shear-thinning/shear-thickening lubricant models, which is very helpful in predicting the performance characteristics of hydrodynamic bearings under harsh industrial operating conditions. The results show that the combined presence of non-Newtonian lubricant and turbulence in the flow significantly affects the steady-state performance parameters of such type of bearing compared to existence of individual presence of turbulence and non-Newtonian lubricant in the clearance space. This work helped to provide better insight into the operation of journal bearings in a severe environment owing to the high speed and changes in the nature of lubricant.

Dynamic characteristics of a non-Newtonian lubrication mechanical seal with herringbone grooves considering cavitation effect

This research investigated the effect of lubricant's non-Newtonian properties on dynamic characteristics of a herringbone grooved liquid film seal (HG-LFS) considering cavitation. A modified steady-state perturbation Reynolds equation of the non-Newtonian was derived. Visualized experiments were conducted to verify the accuracy of calculations. The non-Newtonian effect on stiffness, cavitation, damping coefficients, and other sealing performance of the liquid film seal at different velocity, pressure and film thickness were discussed and analyzed. The results indicate that the seal has larger stiffness and damping coefficients with the dilatant lubricant, the cavitation can be inhibited by the shearing-thinning lubricant, and the impact of non-Newtonian on the seal stability decreases with the increase of film thickness. This study would contribute to the design and theoretical research of liquid film seals.

Thermo-hydrodynamic Analysis of Misaligned Journal Bearing Considering Surface Roughness and Non-Newtonian Effects

This paper presents a numerical simulation for the combined effect of surface roughness and non-Newtonian behavior of the lubricant on the performance of misaligned journal bearing. The modified Reynolds equation to include the effect of non-Newtonian lubricant and bearing surface roughness has been formulated. The model accounts for the lubricant viscosity dependence on temperature and shear rate. In order to make a complete thermo-hydrodynamic analysis (THD) of rough surface misaligned journal bearing lubricated with non-Newtonian lubricant, the modified Reynolds equation coupled with the energy, heat conduction equations, the equation related the viscosity and temperature with appropriate boundary conditions have been solved simultaneously. The performance characteristics of the bearing were presented with different roughness parameter for the pressure, temperature, load carrying capacity, misalignment moment and friction force. The computer program prepared to solve the governing equations of the problem has been verified by comparing the results obtained through this work with that published by different workers. It has been foundthat the results are in a good agreement .The results obtained in the present work showed that the surface roughness characteristics of opposing surfaces and its orientation play an important role in affecting the performance parameters of the bearing. It has been shown that the load in rough aligned journal bearing is higher than that in rough misaligned journal bearing for all surface roughness patterns (γ). An increase in load has been calculated and found to be 29.5% for the bearing with moving roughness while it becomes32% for the bearing with stationary roughness.

Variational principle for a generalized Rabinowitsch lubrication

This paper adopts Rotem and Shinnar?s modification of the Rabinowitsch fluid model for the one-dimensional non-Newtonian lubrication problem, a variational principle is established by the semi-inverse method, and a generalized Reynolds-type equation is obtained. This article opens a new avenue for the establishment of Reynolds-type equation of complex lubrication problems.

A study of double layer conical porous hybrid journal bearing operated with non-Newtonian lubricant

This study deal with the numerical simulation of a hybrid double layer conical porous bearing (DCPB) considering the synergistic effects of a double layer porous matrix and non-Newtonian lubricant (cubic law model) behaviour. The present study investigates the interactive effects of the non-linear factor of lubricant, permeability parameter and semi cone angle on the performance of a hybrid DCPB. The modified Reynolds equation is solved using the finite element technique for a hybrid DCPB. Findings of this study indicate that the DCPB improve the performance parameters as compared to hybrid single layer conical porous bearing (SCPB). Further, the use of non-Newtonian lubricant improves the stability threshold speed margin ω̅th and reduces the frictional power loss (p̅fric).

A study of misaligned compliant journal bearings lubricated by non-Newtonian fluid considering surface roughness

To study the static behavior of misaligned journal bearings under heavy loads using a non-Newtonian lubricant (pseudoplastic fluid, the flow behavior obeys a power-law relationship). And the generalized average Reynolds equation for rough journal bearing under pseudoplastic lubricant flow is derived. The establishment method of the model equation adopts the average flow method of Patir and Cheng. The numerical solution of bearing performance parameters applies the finite difference method and the successive over-relaxation method. And surface roughness can partially offset the effects of liner elastic deformation and lubricant shear thinning. The generalized average Reynolds equation derived in this paper is not only used in the research of hydrodynamic lubrication but also can be used in the research of mixed lubrication.

Effect of Engineered Roughness on the Performance of Journal Bearings Lubricated by Bingham Plastic Fluid Using Computational Fluid Dynamics (CFD)

A journal bearing is a machine element that is used to keep the shaft rotating about its axis. The increasing demand for journal bearing applications in high-speed machines that are efficient and economical has resulted in the need for improvements to the acoustic and tribological performance of journal bearings. In order to improve the tribological and acoustic performance, this study aims to propose a novel journal bearing design by introducing a roughness condition in a specific zone of the stationary bearing surface. In addition, the impact of the application of engineered roughness on the performance of Bingham-plastic-lubricated bearings is investigated in more detail. Considering the effect of cavitation, the analysis was conducted using a 3D computational fluid dynamics (CFD) model of a journal bearing. In comparison with the Reynolds equation—which is inertialess—for lubrication analysis, the use of a 3D CFD model based on Navier–Stokes equations reflects more detailed flow characteristics. Moreover, in this work, variations in the area of surface roughness were employed, resulting in various roughness patterns on the surface of the journal bearing, so that the acoustic and tribological performances of the journal bearing were anticipated to be enhanced. The findings of this study show that under non-Newtonian lubrication of the bearing, the engineered roughness has a strong effect in altering the tribological performance. Furthermore, the well-chosen roughened surface was proven to be more pronounced in enhancing the load support and reducing the friction force. The simulation results also show that using an engineered surface has little effect on the noise of the bearing.

HACIA PRÓTESIS DE RODILLA MÁS DURADERAS: EL MODELO DE PHAN-THIEN YTANNER Y LA LUBRICACIÓN ELASTOHIDRODINÁMICA

The synovial fluid is usually assumed to be Newtonian despite its viscoelastic behavior. In this work a model based on the Reynolds equation and the Phan-Thien and Tanner rheological law (PTT) is presented. The model, of the ellipsoid-on-plane type, contemplates the curvature of the articular surfaces and assumes the tibial component, typically made of ultra-high molecular weight polyethylene (UHMWPE), is deformed according to the column model. Using commercial software COMSOL Multiphysics version 5.2, the governing equations of non-Newtonian lubrication flow were simultaneously solved to find the component of the total stress tensor for the PTT model, in the direction perpendicular to the flow, and the lubricating film thickness. From these results the friction forces and friction coefficients on the articular surfaces were calculated. Simulations were carried out for different operating conditions corresponding to elasto-hydrodynamic lubrication, the predominant lubrication mechanism in the simple support phase of the gait cycle. The results show the importance of an adequate model to obtain quantitative information, considering the fluid as Newtonian would lead to overestimations of the lubricant film thickness. The results suggest that, as long as thin film lubrication is the lubrication regime, the viscosupplementation and consequent increase in relaxation constantλwouldlead to lower coefficients of friction. However, for the lubrication regime to be thin film lubrication, the relaxation constant of the fluid should be less than 2.5×10−5s.

Shear-Thinning and piezoviscous lubricant behavior of spiral grooved hybrid thrust pad bearing configurations

The present study investigates the effects of shear-thinning and piezoviscous lubricant on the behavior of inwardly and outwardly spiral grooved hybrid annular thrust pad bearing configurations. The performance of spiral grooved circular and annular hybrid thrust pad bearing configurations with a capillary restrictor is also compared in this study. The influence on fluid film reaction, lubricant flow rate, fluid film stiffness, and damping coefficients have been carried out. The numerically simulated results show that the synergistic effect of spiral grooves and shear-thinning and piezoviscous behavior of the lubricant, have a significant impact on lubrication performance. The maximum percentage difference in the value of fluid film stiffness between outwardly spiral grooved annular recessed hybrid thrust pad bearing with non-Newtonian lubricant and inwardly spiral grooved annular recessed hybrid thrust pad bearing with Newtonian lubricant is found to be 80.6 percent.

Performance of rough surface hydrodynamic circular and multi-lobe journal bearings in turbulent regimes

This article deals with the steady and dynamic performance analysis of rough surface circular and multi-lobe journal bearings operating with non-Newtonian lubricant in turbulent regimes. The numerical solution of Reynold's equation was obtained using the finite element method. To account for surface roughness, the Patir and Cheng model was used, and fluid turbulent behavior was modeled using the turbulent theory as proposed by Ng and Pan. The non-Newtonian behavior of the lubricant is presented by the Rabinowitsch fluid model, and JFO boundary conditions are used to solve Reynold's equation, considering gaseous cavitation. The bearing with micro-roughness has been considered in numerical analysis and transverse roughness has been reported to improve bearing performance indices. Among the different bearing design configurations, the two-lobe bearing configuration provides significantly improves the minimum film thickness, hydrodynamic pressure, and dynamic parameters. The presence of turbulent flow and transverse surface roughness produces a synergistic effect that enhances the minimum film thickness, stiffness, and damping parameters of journal bearings. This study provides a detailed comparison between various bearing designs and recommends the use of two-lobe bearings for high-speed applications.

Non-Newtonian Thermo-Elastohydrodynamics and Sub-Surface Stress Field of High-Performance Racing Spur Gears

Meshing teeth pairs of involute spur gears often form the final drive of high-performance motorsport transmissions. They are subject to high normal and shear loading. Under transient conditions pertaining to a meshing cycle, the contact conditions alter from the onset of teeth pair engagement through to maximum normal loading, followed by contact separation. Sliding motion only ceases instantaneously at the pitch point. The regime of lubrication remains mostly in non-Newtonian thermo-elastohydrodynamic conditions. The results show that a starved inlet boundary is attained throughout most of the meshing cycle which leads to the diminution of the pressure spike at the exit from the contact conjunction. The reversing sub-surface shear stresses are the main source of the onset of any inelastic deformation, which is dominated by the primary pressure peak in compliance with the Hertzian maximum pressure. The shear stress field is supplemented by an induced field due to the presence of the pressure spike. Under starved conditions this secondary stress field is diminished. The combined solution of elastohydrodynamics with a thermal network model, non-Newtonian lubricant traction, and sub-surface stress evaluation provides for a comprehensive solution not hitherto reported in the literature.

Performance Comparison of Newtonian and Non-Newtonian Fluid on a Heterogeneous Slip/No-Slip Journal Bearing System Based on CFD-FSI Method

It is a well-known fact that incorporating a slip boundary into the contact surfaces improves bearing performance significantly. Regrettably, no research into the effect of slip on the behavior of journal bearing systems operating with non-Newtonian lubricants has been conducted thus far. The main purpose of this work is to explore the performance comparison of Newtonian and non-Newtonian fluid on a heterogeneous slip/no-slip journal bearing system. The tribological and acoustic behavior of journal bearing is investigated in this study using a rigorous program that combines CFD (computational fluid dynamics) and two-way FSI (fluid–structure interaction) procedures to simulate Newtonian vs. non-Newtonian conditions with and without slip boundary. The numerical results indicate that irrespective of the lubricant type (i.e., Newtonian or non-Newtonian), an engineered heterogeneous slip/no-slip pattern leads to the improvement of the bearing performance (i.e., increased load-carrying capacity, reduced coefficient of friction, and decreased noise) compared to conventional journal bearing. Furthermore, the influence of the eccentricity ratio is discussed, which confirms that the slip beneficial effect becomes stronger as the eccentricity ratio decreases. It has also been noticed that the Newtonian lubricant is preferable for improving tribological performance, whereas non-Newtonian fluid is recommended for lowering bearing noise.

Analysis of textured journal bearing with slip boundary condition and pseudoplastic lubricants

The present study investigates the combined influence of slip boundary condition and non-Newtonian lubricants on the tribological performance of hydrodynamic textured journal bearing. To accurately predict the effect of air/vapor bubble formation in diverging zone of the slip-texture bearing, the modified Reynolds equation with considering the Elrod cavitation model has been solved. In addition, the energy equation under adiabatic condition has been also solved for including the loss of viscosity with the temperature rise of lubricant. It has been observed that slip-texture bearings with change in rheology of lubricant from Newtonian to Pseudoplastic shows significant improvement in the maximum pressure, the average rise in temperature, and lubricant-bearing friction-force. Further findings of the study indicate that the combined effect of slip boundary condition and micro-texture with suitable selection of lubricant rheology is beneficial in increasing the stability of hydrodynamic lubricant film in the journal bearings.