Newtonian Lubricant Research Articles

Theoretical Analysis of Orifice Compensated Symmetric and Asymmetric Hydrostatic Non-Recessedjournal Bearings Under Couple Stress Lubricants

In this research a hole-entry hydrostatic journal bearings with couple stress and Newtonian lubricants have been examined analytically. The Newton Rapshon Method and Finite Element Method have been applied on Reynolds equation for couple stress and for the Newtonian lubricants to achieve the film pressure. The results of disparate factors of couple stress lubricants and the external load have been modeled. The outcome of the achieved results showed that the static and dynamic actions of bearings enhanced under a couple stress lubricants assessed the bearings performance with Newtonian lubricant.

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.

Viscoelastic flow with slip in a hyperbolic channel

We study theoretically the steady viscoelastic flow in confined and symmetric hyperbolic channels considering slip along the walls. Under the lubrication approximation and a variety of constitutive models, a high-order perturbation solution with respect to the Deborah number is calculated. The solution for all the field variables (velocity, pressure, and extra-stress) is found analytically up to eighth order and is used along with proper acceleration techniques to achieve convergence up to order one Deborah number. We reveal that even in the presence of slip, the pressure drop decreases monotonically with increasing the fluid elasticity. We evaluate the influence of slip in terms arising from two different decompositions of the pressure drop obtained with the aid of the total force balance and the mechanical energy balance of the flow system. In contrast to the nonslip Newtonian flow, our analysis also showed that the fluid slip along the walls introduces variations in the strain rate at the midplane with the distance from the inlet. However, these are small, and an effective strain rate can be well-represented using a previously developed formula [Housiadas, K. D., and A. N. Beris, Phys. Fluids 36(2), 021702 (2024)]. We also show that when the solution for the midplane velocity is used in the general formula for the Trouton ratio, instead of the Newtonian lubrication solution, there are no appreciable changes, thus confirming the validity and accuracy of our previously reported results [Housiadas, K. D., and A. N. Beris, J. Rheol. 68(3), 327–339 (2024)].

On the elongational viscosity of viscoelastic slip flows in hyperbolic confined geometries

We study theoretically the elongational viscosity (or Trouton ratio, in dimensionless form) for steady viscoelastic flows in confined and symmetric hyperbolic tubes considering Navier-type slip along the wall(s). Both the planar and the cylindrical axisymmetric geometrical configurations are addressed. Under the classic lubrication approximation, and for a variety of constitutive models such as Phan-Thien and Tanner, Giesekus, and Finite Extensibility Nonlinear Elastic with the Peterlin approximation models, the same general analytical formula for the Trouton ratio is derived as for the Oldroyd-B model, in terms of the velocity at the midplane/axis of symmetry and the Deborah number only. Assuming that the velocity field is approximated by the Newtonian lubrication profile, based on our previous study in the absence of slip, we show that a constant extensional strain rate can be achieved in the limits of zero or infinite slip. For finite slip, a slight modification of the geometry is required to achieve a constant strain rate. In these cases, the formula for the steady state Trouton ratio reduces to that for transient homogeneous elongation. We also provide analytical formulae for the modification (decrease) for both the extensional strain rate and the Hencky strain achieved in the confined geometries because of introducing wall slip.

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.

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.

Influence of geometric shapes of recess on the performance of MR lubricated multi-recessed hybrid spherical thrust bearing

This paper aims to investigate the impact of different geometric shapes of recesses/pockets on the behavior of a multi-recessed hybrid spherical thrust bearing (MHSTB) configuration along with MR (magnetorheological) lubricant behavior. The analysis employs a finite element approach to assess the behavior of MHSTB configurations lubricated with MR fluids, with the MR lubricant's behavior modeled using the Herschel–Bulkley model. The governing equations are solved through Galerkin's discretization method combined with a suitable iterative technique. The study reveals significant variations in bearing performance when altering the magnetic field intensity and axial eccentricity ratio. The study explores various geometric recess shapes (i.e., elliptical, circular, triangular, and square) within the MHSTB configuration while maintaining same bearing operating and geometric parameters. Numerical simulations demonstrate that MHSTB systems operating with MR lubricant exhibit higher fluid film reaction and damping coefficients compared to Newtonian lubricant. Furthermore, it is observed that the elliptical recessed bearing configuration outperforms square, triangular, and circular recessed bearing configuration in terms of fluid film reaction and lubricant flow rate.

Dynamic behavior of hydrostatic squeeze film dampers fed through four capillary restrictors with micropolar lubricant

PurposeThe purpose of this research is to study the dynamic behavior of hydrostatic squeeze film dampers made of four hydrostatic pads, fed through four capillary restrictors with micropolar lubricant.Design/methodology/approachThe modified version of Reynolds equation is solved numerically by the finite differences and the Gauss–Seidel methods to determine the pressure field generated on the hydrostatic bearing flat pads. In the first step, the effects of the pad dimension ratios on the stiffness and damping coefficients are investigated. In the second step, the damping factor is evaluated with respect to the micropolar properties.FindingsThe analysis revealed that the hydrostatic squeeze film dampers lubricated with micropolar lubricants produces the maximum damping factor for characteristic length of micropolar lubricant less than 5, while the same bearing operating with Newtonian lubricants reaches its maximum damping factor at eccentricity ratios larger than 0.4.Originality/valueThe results obtained show that the effects of micropolar lubricants on the dynamic performances are predominantly affected by the pad geometry and eccentricity ratio.

An analytical study on nonlinear viscoelastic lubrication in journal bearings

This paper presents a novel analytical solution for journal-bearing viscoelastic lubrication using the perturbation method. The nonlinear Giesekus model was used for the constitutive equations to study the effects of fluid elasticity, shear-thinning viscometric functions, and strain-hardening elongational viscosity of viscoelastic lubrication. The investigation focuses on the impact of characteristic parameters such as mobility factor, eccentricity ratio, and Weissenberg number on the fluid film pressure distribution, load capacity, and shear stress. Although distinguishing between the normal stress differences and extensional viscosity in mixed viscoelastic flows is complicated, we investigated the role and contribution of these two factors. By increasing the elasticity of the fluid, the portion of both mentioned parameters increases consequently. Furthermore, analyses and comparisons show the contributions of the first normal stress and elongational viscosity to the load capacity of the bearing through the stress ratio and flow type parameter for the first time. The research findings indicate that fluid elasticity enhances the load capacity of the bearing compared to a Newtonian lubricant with the same effective viscosity. Moreover, the bearing load capacity is divided into two regions. In the linear region, the mobility factor and Weissenberg numbers have minimal effects leading to a linear increase in the load distribution, and in the exponential region, the load capacity changes are considerable. This research provides valuable insights into the behavior of viscoelastic lubrication in journal-bearing systems.

The impact of tribometer motion and surface roughness on the frictional regimes of model foods

Assessing the tribological behavior of soft materials is often challenging due to the deformative nature of the surfaces which influences the lubricant entrainment and the contact area. The surface roughness and the tribological motion (e.g. sliding, rotational) of the tribometer may also influence the contact area, surface deformation and fluid entrainment. In the present work, we uncover how the above-mentioned parameters influence the lubrication behavior of Newtonian lubricants and of hydrogel microparticle suspensions. Unique to this study is that we use four different tribometers to obtain a more complete picture of the effect of tribometer characteristics on the frictional behavior. We present a side-by-side analysis of four tribological devices: three commercially available tribometers (Anton Paar, Bruker, PCS Instruments) and a custom-made 3D-printed tribometer. With this qualitative analysis, we demonstrate how the different Stribeck regimes are influenced by tribometer motions. The friction coefficients in the boundary regime and the length of the regime are strongly influenced the tribometer used while the slope in the mixed regime only shows minor differences for different tribometers. In the EHL regime, the slopes found correspond with the theoretically predicted value of 0.5 for the rotational tribometers. The linearly oscillating tribometer, however, displays an additional increase beyond the EHL regime with a much steeper slope than expected, which is caused by the specific motion of the tribometer. We further confirm the influence of tribometer motion by introducing hydrogel particle suspensions as model foods; each tribometer shows different lubrication regimes that are specific for each of the devices, highlighting the system dependency of tribological measurements.

Performance analysis of annular disks with non-Newtonian Rabinowitsch fluid model: Influence of squeeze film pressure, surface roughness, porosity and viscosity variation

In various systems of energy, such as turbo-machinery and viscous-lock system, squeeze film plays a crucial role for improving transport systems. The importance of the aforementioned applications led us to explore the physical behavior of Rabinowitsch fluid flow for several values of viscosity, [Formula: see text], load capacity [Formula: see text], nonlinear factor, [Formula: see text], dimensionless film thickness [Formula: see text], dimensionless radius of the capillary tube [Formula: see text], dimensionless thickness of porous pad [Formula: see text]), inner and outer radius ratio [Formula: see text], roughness parameter [Formula: see text] through a squeeze film with two rough porous annular discs. Five-point Gauss quadrature integral formula has been used to examine the characteristics of annular discs, and small perturbation method has been used to discretize the governing Rabinowitsch fluid flow (RFF) equations. The modified Reynolds equation for rough, porous and viscosity change with film thickness is developed using Christensen’s stochastic theory, modified Darcy’s theory and the association between viscosity and film thickness agreement. The impacts of [Formula: see text] on the behavior of porosity and viscosity variability of RFF have been visually depicted in terms of film pressure, load capacity and squeeze reaction time of annular discs. It has been determined that for RFF with variable viscosity and roughness parameter on a porous media, the performance of the annular disks enhances for [Formula: see text] (dilatant lubricant), and diminishes for [Formula: see text] (pseudo-plastic lubricant). It has been found that the film pressure in case of dilatant lubricant is increased by the influence of Rabinowitsch fluids on porous walls, but the behavior of pseudo-plastic lubricants has an opposite tendency relative to Newtonian lubricants. It has also been found that the impact of variability in porosity, roughness and viscosity diminishes the load-carrying capacity (LCC) with increased film thickness than the case of nonporous, smooth surface and constant viscosity of Rabinowitsch fluid.

Piezoviscous-polar lubrication of capillary compensated hybrid conical undulated journal bearing

Linear harmonic vibration during machining of a conical journal may produce micron order undulations on outer surface of journal. Further, a lubricant comprising of long chain polymer additives may attain polar effect due to couple stresses. At high pressure conditions, pressure viscosity interaction in oil may affect the actual viscosity of the lubricant. The flow behaviour of piezoviscous-polar lubricant in a conical bearing is modelled in cylindrical coordinates. FE analysis is utilized to solve the modified Reynolds equation. The results indicate that journal undulations offer relatively higher oil film pressure due to local convergence in oil film, consequently exhibit higher stiffness coefficients. Moreover, piezoviscous-polar lubricant may raise the values of S¯zzupto 18% and C¯zz upto 32% than Newtonian lubricant.

Analysis of the steady-state pressure profile of a double-layered porous journal bearing under turbulent regimes

This theoretical investigation presented the steady-state pressure profile analysis of a hydrostatic double-layered porous journal bearing dealing with the Newtonian lubricant, including the effect of turbulence. Based on Beavers–Joseph's criterion for slip flow, the modified Reynolds equation applicable to finite porous journal bearings lubricated with Newtonian fluids has been derived. The governing equations for flow in the coarse and fine layers of porous medium and the modified Reynolds equation are solved simultaneously using the finite difference method satisfying appropriate boundary conditions. The effect of various design parameters (namely Reynolds number, slenderness ratio, eccentricity ratio, permeability factor, bearing number, and bearing feeding parameter) on the steady-state pressure profile of bearing is presented for both slip and no-slip conditions under laminar and turbulent flow.

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 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.

Hydrodynamic effect of technological lubrication and friction modes formation at sheet rolling

One of the main engineering industries is the processing of metals by pressure. Its purpose is the formation of products from metal blanks of simple forms. An important role in this case belongs to the technology of sheet rolling. The solution of issues related to the choice of optimal modes of sheet rolling is relevant for specialists in the field under consideration. The process of rolling metal products is special, since the contact stresses can exceed the deformation resistance of rolled metal by several times. The tasks of predicting the quality of products, taking into account the prevention of sheet metal continuity defects, as well as the study of technological operations reliability of rolling process are associated with the solution of industrial and scientific problems in this area. Domestic and foreign researchers have noted a significant influence of external friction in the deformation center on the technological parameters of rolling process and quality of the resulting metal products. It is known that rolling is impossible without external friction between metal and roll. The reduction of friction provides an opportunity to increase the economic indicators of sheet rolling, and the rolling production technology itself has significant opportunities for further improvement. Technology of sheet rolling in the conditions of hydrodynamic friction mode allows modeling of friction conditions in the deformation zone. Taking into account the hydrodynamic effect of lubrication allows us to assess the influence of technological factors on the conditions of contact friction during metal pressure treatment and to control the rolling process. Regularities of the flow of liquid Newtonian lubricant are investigated, taking into account features of the deformation zone geometry during sheet rolling. Pumping capacity of the lubricating wedge during rolling is determined, which allows us to explain the regularities of lubrication influence on friction conditions. As an example, the results of calculation of the lubricant pressure depending on the rolling speed are presented. The rolling speeds that provide a liquid friction mode are given. The obtained relations allow us to estimate the influence of contact friction on technological parameters of sheet rolling and can be used in technological calculations of this process

Effect of slip boundary condition and non-newtonian rheology of lubricants on the dynamic characteristics of finite hydrodynamic journal bearing

In the present study, the influence of various slip zone locations on the dynamic stability of finite hydrodynamic journal bearing lubricated with non-Newtonian and Newtonian lubricants has been investigated. Linearized equation of motion with free vibration of rigid rotor has been used to find the optimum location of the slip region with maximum stability margin limit. It has been observed that bearing with interface of slip and no-slip region near the upstream side of minimum film-thickness location is effective in improving the direct and cross stiffness coefficient, critical mass parameter, and critical whirling speed. The magnitude of dynamic performance parameters with slip effect is highly dependent on the rheology of lubricant. Shear-thinning lubricants combined with slip boundary condition shows higher dynamic stability as compared to the Newtonian lubricants under the conventional boundary condition. For all considered rheology of lubricants, the dynamic stability of bearing with slip effect is improving by increasing the eccentricity ratio.

Analysis of Transmission Efficiency of Herringbone Gear with Elastohydrodynamic Lubrication Theory

This paper takes the herringbone gear as the research object, and analyzes the transmission efficiency of the herringbone gear by using the theory of non Newtonian fluid line contact elastohydrodynamic lubrication. Firstly, the oil film pressure and thickness of the contact area are obtained, then the friction coefficient distribution and transmission efficiency in the herringbone gear mesh area are obtained. Finally, the influence of various parameters on the transmission efficiency is analyzed.

Thermal Analysis of Journal bearing with controlled slip/no-slip boundary condition and Non-Newtonian Rheology of lubricant

This paper discusses the combined effect of Non-Newtonian rheology of lubricants and slip boundary condition on the static performance characteristics of finite hydrodynamic journal bearings. A modified JFO model with an adiabatic energy equation has been used for calculating the variation of performance parameters. It has been observed that shear-thinning lubricant with slip effect on partial circumferential region shows a significant percentage of improvement in load-carrying capacity and coefficient of friction. Further, For eccentricity ratio of less than 0.2, these lubricants give maximum tribological performance as compared to Newtonian lubricants under conventional boundary condition.

Control of self-excited rotor disturbances in three-lobe journal bearing space using a couple stress lubricant

In this study, the dynamic behavior of three-lobe noncircular hydrodynamic journal bearings lubricated with couple stress fluid is presented. Currently, application of journal bearings with different geometries such as lobed bearings and using non-Newtonian lubricants, including various additives, are the common suggested solutions by tribology researchers to improve the performance of rotor-journal bearing systems. Due to the incompatibility of new lubricant behaviors including polymer chains or other types of suspended particles with considerable size from the classic Navier–Stokes equations, different models such as couple stress fluid theory have been proposed to evaluate their performance. To investigate the self-excited rotor disturbances caused by various factors, like operating in critical speeds, simultaneous solution of governing Reynolds equation of oil lubricant and the rotor motion equations has been done. The result of dynamic analyses using linear and nonlinear approaches indicates the possibility of enhancing the stiffness and damping ability of the three-lobe bearings by strengthening the couple stress properties of lubricant. It is seen from the results that by increasing the couple stress parameter of oil, the type of rotor perturbations in the bearing clearance space changes from divergent oscillations, as a leading cause of collision between the rotor surface and the bearing shell, to limit cycle motion around the rotor stable position or convergent fluctuations to the static equilibrium point. This improvement in the stability range of three-lobe journal bearings using a couple stress lubricant appears in the results of a linear analysis model in terms of increasing the critical mass parameter and decreasing the whirl frequency ratio. In addition, bifurcation diagram results show that using noncircular three-lobe bearings instead of circular types and replacing the Newtonian lubricant with the couple stress fluid improve the dynamic stability of rotor- bearing supports.