A Study of Palm Oil and Engine Oil Viscosity Effect by Using CFD

Computational fluid dynamics study to investigate the performance of fluid film journal bearings with different geometries

Mathematical model of long journal bearing with incompressible oil flow in field of centrifugal inertia forces acting in lubrication layer of planet wheel journal bearing is developed. Modification of Reynolds equation based on Navier-Stokes equations is received, taking into account centrifugal forces’ impact on fluid film in oil gap of journal bearing. Model was verified by commercial software, which uses full Navier-Stokes equations. Results of verification shows considerable contribution of centrifugal inertia forces on total pressure distribution in journal bearing, carrying force and attitude angle.

This paper presents an analysis of the pressure distribution of hydrodynamic journal bearing for different surface texture, velocity variation and load variation. The performance of journal bearing depends on speed, load carrying capacity, viscosity of oil and temperature condition. Therefore, the effects of these parameters on the performance of journal bearing, on the pressure distribution and on the load carrying capacity have been analyzed on the basis of number of revolution per minute of the shaft. The lubricating oil used for the experimental work is SAE 40. Eight pressure distribution profiles were generated by making eight combinations of speed of the shaft and load on journal bearing. It was observed from the profiles that texture bearing can sustain at more pressure as compared to the smooth bearing. Reason behind this result is the presence of holes in texture bearing. These holes behaves like a reservoir and lubricating oil was filled in it, due to which metal to metal contact reduced and friction was minimized. Hence the performance of the bearing was improved.

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.

High-viscosity plastic fluids and polymer liners are expected to improve the lubrication and load-carrying performance of low-speed and heavy-load journal bearings. The objective of this paper is to investigate the elastohydrodynamic lubrication performance of compliant journal bearings lubricated with non-Newtonian plastic fluids (following the Herschel-Bulkley model) using computational fluid dynamics (CFD) and fluid-structure interaction (FSI) methods. The following data are obtained: fluid film pressure, total bearing deformation, cavitation volume fraction, bearing capacity, and coefficient of friction. The simulation results are in close agreement with the data reported in the existing literature. A comparative analysis of the lubrication characteristics of journal bearings with Babbitt metal, PEEK, and PTFE liners at varying rotational speeds is presented. The effects of yield stress, power-law index, elastic modulus, and liner thickness on the lubrication characteristics are investigated. The results indicate that the power-law index of non-Newtonian plastic fluids has a greater influence on the bearing lubrication performance than the yield stress. Increasing the power-law index could improve the bearing capacity and reduce the coefficient of friction. The research provides a theoretical basis for the application of non-Newtonian plastic fluid-lubricated polymer journal bearings in low-speed and heavy-load equipment.

Due to the wide range of journal bearings applications in the industrial machine, significant efforts have been made by tribology researchers to improve their performance in recent years. Designing new bearings geometry and using lubricants with new chemical compounds including additives are the most common solutions proposed to enhance the performance of journal bearing supports. New advancements in nanotechnology and producing the various types of nano particles have provided the chance of upgrading the properties of commercial lubricants. According to the different effect of nano fluids on the performance of mechanical systems corresponding to their composition, today they are used to achieve different goals in lubrication systems. Upgrading the steady state performance parameters including load carrying capacity, attitude angle, surface cooling and effective viscosity are among the expected results of applying nano lubricant in journal bearings. So, in this study the performance of hydrodynamic two lobe journal bearings lubricated with SiO2-multiwall carbon nano tubes /SAE40 hybrid nano fluid is presented considering the thermal effects. For this purpose, the governing Reynolds and energy equations as well as the equation of heat transfer in bearing shell are modified based on the properties of assumed rotor-bearing system. Then the effects of solid volume fraction of nano particles on the performance of two lobe bearings are studied for different amount of bearing noncircularity. The results indicate that upgrading the solid volume fraction of added nano particle to the SAE40 base oil, enhances the lubricant pressure distribution, load carrying capacity, and lubricant effective viscosity. Further, by increasing the solid volume fraction, the attitude angle and temperature of lubricant and rotor-bearing surfaces experience a decreasing trend. Generally, it's obvious from the results that choosing the appropriate solid volume fraction of SiO2-multiwall carbon nano tubes in hybrid nano oil composition, especially for high value of preload factor, can improve the performance of two lobe bearings.

This paper investigated the eccentricity ratio, relative clearance, and length to diameter ratio under different load carrying capacities and journal rotation speeds, aiming to provide design reference of eccentricity ratio, relative clearance, and length to diameter ratio in water-lubricated bearing design process. The computer fluid dynamics was adopted to analyze eccentricity ratio, relative clearance, and length to diameter ratio of water-lubricated bearing. The cavitation effect of water was considered in the analysis. The simulation results of eccentricity ratio were verified by experiments. In different journal rotation speeds, the relative clearance had little influence on the maximum water film pressure and load carrying capacity. The numerical number of maximum water film pressure and load carrying capacity was in a small range. Designing chart of eccentricity ratio, relative clearance, and length to diameter ratio was provided.

The performance characteristics of a thin film lubricated journal bearing are investigated by means of three-dimensional computational fluid dynamics analysis. The 3D Navier Stokes compressible equations were integrated to simulate the flow. Turbulence effects were included in the computation of unsteady transient analysis of journal bearing, taking into account gravity. The Journal bearing is designed in Gambit software, the journal is modeled as a ''moving wall'' with an absolute rotational speed of 3000rpm. The flow is simulated using Ansys Fluent software. Design parameters like relative eccentricity, dimensionless load carrying capacity, dimensionless wall shear stress, friction coefficient, Reynolds number, Sommerfeld number, strain rate, pressure distribution, temperature distribution and lubricant flow properties like turbulent viscosity, and velocity magnitude are considered for the analysis. It is assumed that the flow of lubricant is laminar and isothermal. Unsteady transient analysis is carried out for the journal bearing with different L/D ratios of 0.25, 0.5, 1, 1.5, and 2 and the corresponding results: relative eccentricity vs. Sommerfeld number, Dimensionless load carrying capacity vs. relative eccentricity, and dimensionless friction coefficient vs. relative eccentricity are presented in the analysis. Index Terms—Eccentricity, journal bearing, load carrying capacity, turbulent dissipation rate, unsteady, wall shear stress. I. INTRODUCTI ON A bearing is a system of machine elements whose function is to support an applied load by reducing friction between the relatively moving surfaces. As modern science and technology is developing, one discovered that the lubricant is affected by the gap of bearing. The interaction degree between the lubricant and solid surface influences the lubrication property of the bearing clearly. A thin film lubricated journal bearing is to develop positive pressure by virtue of relative motion of two surfaces separated by a fluid film. Thin film bearings are those in which although lubricant is present, the working surfaces partially contact each other at least part of the time. These bearings are also called Boundary Lubricated Bearings. Recently, following the progress in computer technology, many researchers began to use commercial computational fluid dynamics (CFD) programs in their investigations. The main advantage of CFD code is that it uses the full Navier-Stokes equations and provides a solution to the flow problem, whereas finite difference codes are based on the Reynolds equation. The results obtained by the two approaches are therefore likely to differ. Moreover, the CFD packages are applicable in very complex geometries.

<div class="htmlview paragraph">Minimum bearing oil film thickness (MBOFT) was measured in both a main and a connecting-rod bearing of a production V-6 engine using the total capacitance method (TCM). MBOFT was measured at 1500 rpm and at three different engine loads (64, 128, and 192 Nm). The oil sump temperature was controlled at 100°C. Five engine oils were tested (SAE grades 5W-20, 20W-20, 5W-30, 10W-30, and 20W-50) with emphasis given to the SAE 5W-30 and 10W-30 oils. MBOFT was also calculated using a computer code.</div> <div class="htmlview paragraph">The absolute minimum of the MBOFT (MBOFT<sub>min</sub>, closest approach between the journal and the bearing) increased with increasing values of a Sommerfeld parameter (viscosity/load) and this dependence was similar in both the main and the connecting-rod bearings. But, for the main bearing the MBOFT<sub>min</sub> values showed a higher dependence on the Sommerfeld parameter than those for the connecting-rod bearing. Similar results were obtained with the theoretical calculations of the MBOFT_<sub>min</sub> values.</div> <div class="htmlview paragraph">The experimental data indicated a 10 percent higher MBOFT<sub>min</sub> for the SAE 10W-30 oil than for the SAE 5W-30 oil in both bearings. This difference was smaller in the theoretical calculations, about 4 percent for the main and 2 percent for the connecting-rod bearing. Uncertainties in the prediction of the oil viscosity at the high temperatures and pressures of the bearing may have been responsible for this difference.</div>

Experimental investigation into surface texture effect on journal bearings performance

This paper aims at the modelling and investigation of unstable journal bearing with an emphasis on instabilities such as oil-whirl or further induced oil-whip. For this reason, a test rig for the investigation of these phenomena was built. Geometry, parameters and operating cases of the rig are described in detail in the presented paper. Computational analysis of the test rig was performed using two methods — the finite element method and a multi-body approach. The calculations of pressure distribution in journal bearings were also performed applying two methods — the finite difference method and the finite element method. The results of the analysis are properly introduced and discussed at the end of this paper. The results suggest that a yet unknown sub-synchronous component may appear under specific conditions. The component typically appears at frequency 0.9–0.98 of shaft speed and is likely caused by a location of a bore for oil supply.

PurposeThis study aims to investigate the combined effects of roughness and ferrofluid lubricant on finite journal bearing load capacity and squeeze time.Design/methodology/approachThe stochastic theory of Christensen is applied to study the surface roughness effect. The Shliomis model is used to take into account the effects of the rotational viscosity of ferromagnetic particles and their magnetic moment. A finite wire located in the center of the shaft produces the applied magnetic field. A developed computing code allows predicting the effect of the surface roughness on the performance of the considered journal bearing. The good agreement with the results of the literature validates the used approach.FindingsThis study shows that unlike longitudinal roughness, the presence of transverse roughness makes the use of ferrofluid more beneficial in terms of increasing the performance of finite journal bearings. This increase is more significant for large relative eccentricities, which present an ideal confinement.Originality/valueThis study shows the effect of two surface roughness patterns on the squeezing performance of a finite journal bearing lubricated by a ferrofluid.

A journal bearing is used to support radial loads under high speed operating conditions. In a journal bearing, pressure or hydrodynamic lift is generated in the thin lubricant oil film that separates the shaft and the bushing, thus preventing metal-to-metal contact. Some journal-bearing configurations are susceptible to large-amplitude, lateral vibrations due to a “self-excited instability” known as oil whirl. In order to investigate the effects of lubricant viscosity on oil whirl, a simplified Thermohydrodynamic analysis (THD) analysis of a plain cylindrical journal bearing system has been developed. The “classical” form of the Reynolds equation coupled with simplified, first-order energy equations are solved in an approximate fashion by assuming a parabolic pressure distribution in axial direction. THD design charts for the rapid evaluation of dynamic coefficients and the threshold speed are developed to investigate the effects of temperature on oil whirl instability. A non-linear transient stability analysis is also presented. This investigation reveals that the inlet viscosity has a pronounced influence on the bearing dynamic coefficients of the lubricating oil film. This investigation also reveals that it is possible to stabilize a journal bearing either by heating the oil or by cooling the oil depending upon the operating region.

Effects of angular misalignment on the performance of rotor-bearing systems supported by externally pressurized air bearing

Objectives: The theoretical examination of the impact of variation in viscosity of micropolar fluid lubricant on dynamic and static characteristics of rough short journal bearings lubrication with squeezing effect and to compare it with the performance of non-viscosity variation. Method: The mathematical model for the physical problem considered, modified stochastic Reynolds type equation assessing for variation in viscosity of micropolar fluid and structure of roughness on bearing surface is inferences by exploiting a random variable having stochastic behavior with non–zero mean, skewness and variance. The analysis is done for both the scenarios of a stable and an alternating applied load. Findings: According to the result, the velocity of the journal center is reduced by the micropolar fluid when there is a cyclic load, and analysis is done on the impact of viscosity variation in micropolar fluid on the squeeze film behaviors of rough short journal bearing reviles that, the viscosity variation parameter is to diminish the pressure and load carrying capacity in squeeze film and increases the velocity of journal center. Novelty: The original research was conducted on the variation in viscosity of micropolar fluid lubricant on dynamic and static behaviors of squeeze film lubrication of rough short journal bearings and results are compared with non-viscosity variation parameter. This, according to the authors’ knowledge of the literature, has not yet been investigated. Keywords: Journal Bearings, Micropolar Fluids, Surface Roughness, Viscosity Variation, Dynamic Loading