non-Newtonian Behaviour Of Lubricant Research Articles

A numerical study on the impact of lubricant rheology and surface topography on heavily loaded non-conformal contacts

The increasing requirement of high-power density (power throughput/ weight) in modern day machines lead to thin film lubrication condition in various machine components (rolling element bearings, gears, cams, etc,) due to severe loading conditions. Surface roughness features and lubricant rheology plays a vital role in thin film lubrication, and significantly affects the lubrication performance and lifetime of machine components. The present work demonstrates surface topography and lubricant rheology effects on the traction coefficient for heavily loaded non-conformal contacts. The load-sharing concept considering elastic-plastic deformation of asperities, and Carreau shear-thinning rheological model is employed to describe the dry rough contacts and non-Newtonian behavior of lubricant. An influence of surface topography parameters such as roughness, skewness, kurtosis, and pattern ratio on the traction coefficient is discussed. From results, it is found that among different surface topographies, negatively skewed surfaces having isotropic surface pattern exhibit minimum traction coefficient. The load share function and the critical rolling speed are determined for various surface topographies which provides further insights into the surface topography effect on traction coefficient. The findings of present study are noteworthy as they provide a theoretical basis for an assessment of the lubrication performance of heavily loaded non-conformal contacts.

Micro-grooved hybrid spherical thrust bearing with Non-Newtonian lubricant behaviour

Recent tribology research has primarily focused on leveraging engineered grooved surfaces to enhance the lubrication performance of tribo-contacts. The performance of fluid film bearings may be improved by using a properly designed micro-groove on the surface of bearing. This paper deals with the performance of micro-grooved hole-entry hybrid spherical thrust bearing (HSTB) considering Non-Newtonian behavior of the lubricant. To analyse the Non-Newtonian behaviour of lubricant the cubic law model has been used. The solution of the governing Reynold equation in the fluid film domain of the hole-entry hybrid spherical thrust bearing is obtained by the FEM. In this study, the influence of rectangular and circular shaped micro-groves has been analysed. The parametric analysis has also been performed to obtain the optimum attributes (i.e. w¯g,d¯g,l¯gr) of the micro-grooves for both the shapes. The present investigation shows that the performance of the hole-entry hybrid spherical thrust bearing gets enhanced by considering the micro-grooves on the surface of bearing. Furthermore, the bearings performance is affected by the geometry of the micro-groove used. The value of fluid film reaction (F¯y) and stiffness coefficient (S¯) is observed to be increased by 23.33% and 343.98% at εy = 0 and κ¯=1 for the case of rectangular-shaped micro-grooved hole-entry HSTB configuration.

CFD analysis of Effect of journal bearing lubricated with non-Newtonian fluid

The present paper deals with the CFD analysis of hydrodynamic bearing lubricated with a non-Newtonian fluid and the non-Newtonian behaviour of lubricant is represented by a power-law. Bearing parameters such as fluid film pressure and load-carrying capacity are determined by varying the power-law index (n) in terms of its viscosity from 0.8 to 1.2 under steady-state conditions through the CFX 17.2 software module and the flow model opted as Laminar based on Reynolds number calculation as per the geometry developed for the simulation. The relationship between the pressure and load-carrying capacity are also obtained for different relative clearance, revolution per minute and L/D ratio. Fluid film pressure profile was drawn by varying input parameters at different power-law index for understanding the performance of HDB under different regimes i.e. dilatant, Newtonian and pseudoplastic fluids. Plots were also created between Pressure, load carrying capacity and power law index to study the performance of HDB. This has been observed that the bearings lubricated with dilatant fluid (n >1) have higher pressure and load carrying capacity as compared to those lubricated with pseudoplastic fluid (n < 1). Occurrences of cavitation were also seen at lower angle with increases in power law index for 0.0006 relative clearance but increases at 0.0008.

Performance behavior of pocketed journal bearing employing non-newtonian lubricant

This paper reports the improvement in the performance behaviors of non-Newtonian fluid lubricated journal bearings employing a rectangular pocket. Coefficient of friction and load carrying capacity of pocketed and non-pocketed bearings are reported and discussed. In the numerical approach, non-Newtonian behavior of lubricant is simulated employing the power law model. Various cases of bearings having different axial length to diameter ratios [(L/D) in the range 0.5–2.0] are considered. Lubricants of different rheology viz. pseudoplastic, Newtonian and shear thickening were employed for lubricating the bearings. Rheology of lubricant is controlled by varying the power law index n in the range 0.9–1.1. Based on the investigation, it is found that the pocketed bearing yields significantly reduced coefficient of friction and higher load carrying capacity in comparison to the non-pocketed bearing. Also, the performance of pocketed bearing improves with the increase in the power law index. Best performance of the pocketed bearing is observed for the bearing having L/D value of 0.5 at high eccentricity ratio when lubricated with the shear thickening fluid (n=1.1).

Performance of textured spherical thrust hybrid bearing operating with shear thinning and piezoviscous lubricants

Improving the lubricating performance of tribo-pairs using engineering textured surfaces has been the main focus of tribology research in recent years. The use of a suitably designed micro-texture on the bearing surface may have a beneficial effect on the performance of fluid film bearings. In the present paper, a mathematical model of a hybrid spherical thrust bearing is developed considering the effect of shear thinning and piezoviscous behaviour of a lubricant. The modified Reynolds equation for a hybrid spherical thrust bearing configuration together with a restrictor flow equation for a capillary restrictor is solved using a finite-element method. In this work, the effect of various micro-textures shapes (spherical, circular, conical and square) and non-Newtonian lubricant behaviour having shear thinning and piezoviscous effects are analysed. The numerically simulated result shows a strong dependence on the combined effect of shear thinning and piezoviscous lubricant behaviour and a chosen geometric shape of a texture. The frictional power loss is seen to reduce nearly by 24.05%, and the stiffness gets enhanced by 11.08%.

Analysis of a double layer porous hybrid journal bearing considering the combined influence of wear and non-Newtonian behaviour of lubricant

Use of porous materials in fluid film is well established so as to make more uniform distribution of pressure along the journal surface. The work presented in this paper deals with theoretical examination into the effect of worn bearing surface on the behaviour of a hybrid double layer porous journal bearing system (DLPJBS) operating with power-law lubricants. The governing equation for the flow of non-Newtonian lubricant in the bearing porous clearance space is solved by using the FEM. The effects of non-Newtonian lubricant on the bearing characteristics of a worn bearing have been studied. Findings of this study indicates that the hybrid DLPJBS operating under non-Newtonian lubricant offers enhanced values of $${\bar{h}}_{min}$$ , $${\bar{\omega}}_{th}$$ and rotor dynamic coefficients (stiffness and damping coefficients).

70 years of Elastohydrodynamic Lubrication (EHL): A Review on Experimental Techniques for Film Thickness and Pressure Measurement

Elastic deformation of surfaces and piezo-viscous effect of lubricant make EHL a very complex lubrication regime. Elastohydrodynamic Lubrication becomes much more complex when conditions like rough surfaces, non-newtonian behavior of lubricant and temperature dependent flow are considered. The present paper takes the task of reviewing experimental methods applied till date for measuring film thickness and pressure. The paper has been divided into many sections and sub-sections to deal with these techniques in a lucid manner. Experimental methods have been categorized into Electrical, Optical and Acoustic methods. The difference of 8–10% between theoretical and experimental results are witnessed using Electrical methods. Whereas, this difference is less than 1% using Optical methods. Among all optical methods, Relative Optical Interference Intensity Technique is the most effective technique with an ability to measure the film thickness as small as 1 nm or less. The last section of the paper deals with the scope of improvement in measurement techniques in future to understand EHL in more detail.

Effect of Kinematic Operating Conditions on Ridge Deformation—Numerical Study With Experimental Comparison

The behavior of roughness features under rolling–sliding inside highly loaded elastohydrodynamically lubricated (EHL) contacts is studied in detail for many years now. In particular, the roughness deformation was subject to different theoretical analyses as well as experiments. A recent experimental work developed by Šperka et al. (2016, “Experimental Study of Roughness Effects in a Rolling–Sliding EHL Contact—Part I: Roughness Deformation,” Tribol. Trans., 59(2), pp. 267–276) studied the effect of kinematic operating conditions (mean velocity and slide to roll ratio) on the deformed profile of a ridge. The current paper presents results of full numerical simulations and their direct comparison to experiments in order to study the dependency of roughness deformation on the operating conditions. The assumption of non-Newtonian lubricant behavior seems to have a significant influence on the results as well. Results indicate that, in agreement with experiments, the variation of mean velocity causes changes in the deformed profiles of roughness while, on the other hand, the magnitude of slide to roll ratio (for sliding larger than ±50%) does not have influence on the size of the deformation.

Performance of 180° partial hole-entry hybrid journal bearing considering the combined influence of surface roughness and non-Newtonian behaviour of lubricant

The present paper is aimed to analyse the static and dynamic performance of a capillary compensated 180° partial non-recessed (hole-entry) hybrid journal bearing system considering the combined influence of surface roughness and nonlinear behaviour of the lubricant. The relation between shear stress and shear strain rate of non-Newtonian lubricant has been modelled by using the power law model. To analyse, the performance of hybrid journal bearing, the governing Reynolds equation has been solved by using the finite element method. The numerically simulated result indicates the effect of surface orientation parameters (γ), power law index (n) and surface roughness parameter (Λ) on the performance characteristics. The present results indicate that, the transverse roughness pattern (γ = 1 / 6) gives better stability of bearing as compared to other roughness patterns. Therefore, a proper selection of roughness parameters (γ and Λ) and power law index (n) is essential to obtain optimum performance of bearing.

Performance of 180° partial hole-entry hybrid journal bearing considering the combined influence of surface roughness and non-Newtonian behaviour of lubricant

Performance of 180° partial hole-entry hybrid journal bearing considering the combined influence of surface roughness and non-Newtonian behaviour of lubricant

Non-Newtonian Starved Thermal-Elastohydrodynamic Lubrication of Finite Line Contacts

Heavily loaded finite line contacts working under elastohydrodynamic lubrication (EHL) conditions are quite often found in machine elements. However, a perfect line contact requires absolute alignment of the axes of the contacting bodies, which is difficult to achieve. In order to overcome this problem and avoid edge loading, one or both of the contacting cylinders are crowned. This article presents a new model for finite length line contacts. In addition to the finite length of the contact and the profile of the contact bodies, the proposed model takes into account the thermal effects, non-Newtonian lubricant behavior, and starved lubrication. The governing equations are solved using the multilevel multigrid technique. The results were validated by comparing film shape and pressure distribution of a finite line contact against an infinite one. The influence of the lubricant starvation and fillet radius on the pressure distribution, film shape, temperature distribution, and friction coefficient are presented. Finally, the effect of alternative roller profiles is shown.

Mathematical modeling of stability in rough elliptic bore misaligned journal bearing considering thermal and non-Newtonian effects

The paper briefly introduces a finite difference method based mathematical model to predict the stability of a finite journal bearing. The proposed method is used to integrate the geometrical irregularities of bearing such as non-circularity and surface roughness with the operational error like misalignment to represent more accurate film thickness. The bearing bore is assumed elliptic with longitudinal or transverse type wave pattern of roughness. A combined solution of Reynolds equation and Energy equation is made using effective influence Newton–Raphson method of error convergence. The non-Newtonian behavior of lubricant is addressed based on Power Law model. Thermal effect is considered adiabatic. Further to this analysis, the steady state and related perturbed pressures are estimated using linearization of bearing reaction. The dimensionless spring and damping coefficients are evaluated to find the critical mass and whirl ratio. Finally, the effect of misalignment bore ellipticity and roughness pattern on stability of such journal bearing is discussed in detail.

Stabilized fully-coupled finite elements for elastohydrodynamic lubrication problems

This work presents a model for elastohydrodynamic (EHD) lubrication problems. A finite element full-system approach is employed. The hydrodynamic and elastic problems are solved simultaneously which leads to fast convergence rates. The free boundary problem at the contact's exit is handled by a penalty method. For highly loaded contacts, the standard Galerkin solution of Reynolds equation exhibits an oscillatory behaviour. The use of artificial diffusion techniques is proposed to stabilize the solution. This approach is then extended to account for non-Newtonian lubricant behaviour and thermal effects. Artificial diffusion procedures are also introduced to stabilize the solution at high loads.

Performance of slot-entry hybrid journal bearings considering combined influences of thermal effects and non-Newtonian behavior of lubricant

This paper presents theoretical investigations of the thermal and rheological effects of lubricant on the performance of symmetric and asymmetric slot-entry hybrid journal bearing system. FEM has been used to solve the Reynolds equation governing flow of lubricant in bearing clearance space along with restrictor flow equation, energy equation and conduction equation using suitable iterative technique. The thermohydrostatic (THS) rheological performance of slot-entry hybrid journal bearings are studied for small temperature variation of the lubricant. The computed results reveal that variation of viscosity due to temperature rise and non-Newtonian behavior of lubricant affects the bearing performance quite significantly.

Film thickness variations in elasto-hydrodynamically lubricated circular contacts induced by oscillatory entrainment speed conditions

In this paper, the effects of an oscillatory entrainment speed on the film thickness in an elasto-hydrodynamically lubricated circular contact operating in the piezo-viscous regime as predicted by a conventional elasto-hydrodynamic lubrication model are described in detail. The relative variation of the film thickness on the centreline of the contact mainly depends on two dimensionless parameters: relative entrainment velocity amplitude and dimensionless entrainment velocity frequency. For small to moderate values of dimensionless frequency, the results can be accurately predicted through a simplified ‘engineering approach’: propagation of inlet modulations along oscillatory characteristics. For values of the dimensionless frequency of O(1), film thickness modulations occur on a sub-contact scale. This work was initiated by the experimental results of Glovnea and Spikes obtained for two lubricants PAO and 5P4E, which have the same ambient viscosity but a different viscosity—pressure coefficient. During the experiments significant difference in behaviour was observed. In this paper, it is shown that a conventional model assuming Newtonian rheological behaviour predicts the same relative film thickness results for both the lubricants. This agrees well with the behaviour observed for PAO, which can be considered as a standard oil that is well characterized by its bulk viscosity, density, and their pressure dependence alone. Nevertheless, further experiments need to be carried out to validate the predictions for larger values of the dimensionless frequency. The behaviour observed in the experiments for 5P4E is significantly different. For accurate prediction of friction, the need to include non-Newtonian lubricant behaviour in models is well known. Film thickness predictions are often less sensitive to the specifics of the lubricant behaviour. However, the results presented here indicate that for film thickness calculations, under rapidly varying conditions in time, more advanced rheological models, including visco-elastic behaviour, may have to be considered as well.

Influence of Surface Roughness on Non-Newtonian Thermohydrostatic Performance of a Hole-Entry Hybrid Journal Bearing

A general solution scheme to account the surface roughness and the cross-film viscosity variation of lubricant due to its non-Newtonian behavior and rise in fluid-film temperature for the analysis of fluid-film bearings is presented. The combined influence of surface roughness, non-Newtonian behavior of lubricant, and thermal effects on the performance of a hole-entry hybrid journal bearing system has been investigated. The surface roughness, especially stationary roughness (i.e., rough bearing and smooth journal) with a transverse pattern was found to partially compensate for the loss in load-carrying capacity due to the thermal and/or non-Newtonian behavior of lubricant effects. It limits 18.86% loss in load-carrying capacity due to the thermal effect to only 1.6% and 33.99% loss due to the combined influence of non-Newtonian lubricant and thermal effect to 16.76%.

Numerical Modeling of Non-Newtonian Fluids in Slider Bearings and Channel Thermohydrodynamic Flow

A three-dimensional thermohydrodynamic model is developed to predict non-Newtonian lubricant behavior in slider bearings and channel flow. The generalized Reynolds equation is established using the concept of generalized Newtonian fluids (GNF) and the temperature field is determined with the energy equation. The chosen rheological models are the power-law, Bingham, and Hershel–Bulkley models. The last two models hold uniformly in yielded and unyielded regions using the approach proposed by Papanastasiou. The results present the evolution of the velocity, pressure, and thermal fields. The power loss, load capacity, and friction coefficient are analyzed. Comparisons are made with Newtonian lubricants and other recent non-Newtonian computational analyses.

Analysis of rough line contacts operating under mixed elastohydrodynamic lubrication conditions

AbstractHeavily loaded machine elements, such as gears, usually operate in the mixed lubrication regime. Surface roughness has a significant effect on the pressure distribution, the subsurface stress field, and the friction coefficient. Based on the superposition of a dry rough and a fully flooded smooth contact, a mixed lubrication model has been developed. The roughness profile is assumed to be known. Surface deformation is calculated by taking into account the pressure distribution that is built up by asperity contacts, asperity interactions, and lubricant flow. Thermal and sliding effects are incorporated into the analysis. Non‐Newtonian lubricant behaviour is considered by using a power‐law rheological model. The pressure distribution, subsurface stress field, and friction coefficient were calculated from the model at several points along the contact path for an FZG type C gear pair. It was shown that a significant part of the load is carried by the contacting asperities. The position of the maximum shear stress is very close to the surface.

Calculation of sliding power loss in spur gear contacts

AbstractAn engineering‐level calculation model for sliding power loss in spur gear contacts is presented. Teeth contact through the line of action is modelled as a constantly changing roller contact whose radius, speed, and load can be calculated from the gear geometry under the given operating conditions. The gear mesh cycle is approximated by a large number of elastohydrodynamic contacts. A constant film thickness and a Hertzian pressure distribution are assumed in each contact. The model includes non‐Newtonian lubricant behaviour together with temperature and mixed lubrication effects in contact. The numerical solver is reasonably fast in evaluating effectively the sliding power loss dependence on the essential gear and lubricant parameters. The features and behaviour trends of the calculated sliding power losses have a close similarity with published results obtained from measurements and experiment‐based power loss models with mineral oil. The limiting shear stress of the lubricant is observed to have an essential role in the power loss behaviour especially at high loads.

Non-Newtonian Effects on the Performance of Dynamically Loaded Elliptical Journal Bearings Using a Mass-Conserving Finite Element Cavitation Algorithm

The effects of non-Newtonian lubricant behavior are investigated numerically for elliptically shaped journal bearings subjected to transient loads. The analysis is based on the mass-conserving finite element cavitation model of Kumar and Booker. The results reveal that non-Newtonian effects have an important influence on journal bearing performance. It is found that there is a significant increase in the maximum film pressure and flow rate whereas a significant decrease in the minimum film thickness and power loss. Presented at the 56th Annual Meeting Orlando, Florida May 20–24, 2001