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1 – 10 of over 20000Sreedhar Babu Kalakada, Prabhakaran Nair Nair Kumarapillai and Rajendra Kumar P K
The purpose of this work is to investigate the static performance characteristics of thermohydrodynamic journal bearing operating under nanolubricants (lubricants containing per…
Abstract
Purpose
The purpose of this work is to investigate the static performance characteristics of thermohydrodynamic journal bearing operating under nanolubricants (lubricants containing per cent weight concentration of nanoparticles).
Design/methodology/approach
Addition of nanoparticles in the lubricant increases lubricant viscosity. To study the effect of this variation on journal bearing, analytical models are developed for the relationship between viscosity, 0-0.5 per cent weight concentration of nanoparticles and temperature range of 300-900°C. To obtain pressure and temperature distribution, modified Reynolds and energy equations are solved by using the finite element method. The viscosity field (varies with temperature and per cent weight concentration of nanoparticles) is updated in these two equations by using the developed analytical model. The steady-state performance characteristics are computed for various values of eccentricity ratios for non-thermoviscous (viscosity of lubricant varies with per cent weight concentration of nanoparticles) and thermoviscous (viscosity of lubricant varies with per cent weight concentration of nanoparticles and temperature) cases. The lubricant and the nanoparticles used for the present work are SAE15W40, copper oxide (CuO), cerium oxide (CeO2) and aluminum oxide (Al2O3).
Findings
The pressure and temperature distribution across the lubricant film in the clearance space of journal bearing and static performance characteristics are calculated.
Originality/value
The computed results show that addition of nanoparticles in the lubricant influences the performance characteristics considerable in thermoviscous case than non-thermoviscous case.
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Boualem Chetti and Wael Ahmed Crosby
The purpose of this paper is to present the effect of the preload on the static characteristics of three-lobe bearings lubricated with a fluid blended with high polymer additives…
Abstract
Purpose
The purpose of this paper is to present the effect of the preload on the static characteristics of three-lobe bearings lubricated with a fluid blended with high polymer additives modeled as a couple stress fluid.
Design/methodology/approach
Based on the micro-continuum theory, the modified Reynolds equation for couple stress fluids is solved using a finite difference method to obtain the distribution of the pressure, the load-carrying capacity, the attitude angle, the friction coefficient and the side leakage for various values of the couple stress parameter and the preload factor.
Findings
The results show that the presence of a couple stress in the lubricants improves the static characteristics of this type of bearing compared to those lubricated with Newtonian fluids for any value of the preload factor. Thus, it is found that the preload significantly affects the performance of the three-lobe journal bearing lubricated with a couple stress fluid or a Newtonian fluid. Moreover, the investigation showed that increasing the preload factor exhibits an increase in the load carrying capacity and the attitude angle, but it decreases the friction coefficient and the side leakage especially at a lower preload factor. Furthermore, using a couple stress fluid and a higher preload factor led to a significant rise in the load carrying capacity and a significant reduction in the friction coefficient.
Practical implications
This study helped improve the performance characteristics of the three-lobe journal bearing.
Originality/value
The presence of couple stress in the lubricants improves the static characteristics of this type of bearing compared to those lubricated with Newtonian fluids for any value of the preload factor. The usage of the couple stress fluid and the higher preload factor led to a significant rise in the load carrying capacity and a significant reduction in the friction coefficient.
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H.C. Garg and Vijay Kumar
This paper aims to investigate the effect of plugging of holes on the static performance characteristics of a constant flow valve compensated hole‐entry hybrid journal bearing…
Abstract
Purpose
This paper aims to investigate the effect of plugging of holes on the static performance characteristics of a constant flow valve compensated hole‐entry hybrid journal bearing system operating with Newtonian and non‐Newtonian lubricants. The analysis considers the generalized Reynolds equation governing the flow of lubricant having variable viscosity in the clearance space and equation of flow of lubricant through constant flow valve restrictor. The non‐Newtonian lubricant is assumed to follow the power law. The performance characteristics are computed for the two values of power law index (n=1.0 and 0.566). The computed results indicate that the blockage of holes during operation will not be the likely causes for the imminent failure of a well‐designed non‐recessed hole‐entry hybrid journal bearing.
Design/methodology/approach
Finite element method has been used to solve generalized Reynolds equation governing the flow of lubricant having variable viscosity in the clearance space and equation of flow of lubricant through constant flow valve restrictor.
Findings
The computed results indicate that the blockage of holes during operation will not be the likely causes for the imminent failure of a well‐designed non‐recessed hole‐entry hybrid journal bearing. The bearing configuration with plugged holes provides sufficient fluid film thickness and low power requirement as less lubricant is required to be pumped in the bearing.
Originality/value
To the best of the author's knowledge, no study which considers the influence of plugging of holes on the static performance characteristics of a constant flow valve compensated hole‐entry hybrid journal bearing system operating with Newtonian and non‐Newtonian lubricant is yet available in the literature.
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Compliant foil thrust bearings are promising bearings for high-speed oil-free turbomachinery. However, most previous experimental and numerical approaches to investigate the…
Abstract
Purpose
Compliant foil thrust bearings are promising bearings for high-speed oil-free turbomachinery. However, most previous experimental and numerical approaches to investigate the performance of these bearings have ignored the effect of bearing runner misalignment. Therefore, this paper aims to evaluate the effects of static and dynamic angular misalignments of the bearing runner on the performance of a gas-lubricated foil thrust bearing.
Design/methodology/approach
The bearing runner is allowed a maximum angular misalignment that produces a minimum gas film thickness as low as 20 per cent of the nominal clearance. Then, the variations of bearing load carrying capacity, viscous power loss and stiffness and damping coefficients of the gas film with runner misalignment are thoroughly analyzed. The flow in the gas film is modeled with compressible Reynolds equation along with the Couette approximation technique, and the deformation of the compliant bearing is calculated with a robust analytical model. Small perturbations method is used to calculate the force and moment dynamic coefficients of the gas film.
Findings
The results show that misaligned foil thrust bearings are capable of developing a restoring moment sufficient enough to withstand the imposed misalignments. Furthermore, the enhanced hydrodynamic effect ensures a stable operation of the misaligned bearing, and the results highlighted the role of the compliant bearing structure to maintain foil bearing prominent features even at misaligned conditions.
Originality/value
The value of this study is the evaluation of the effects of runner angular misalignments on the static and dynamic characteristics of Generation II bump-type foil thrust bearing.
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Sanjay Sharma, Gourav Jamwal and R.K. Awasthi
The purpose of this paper is to provide the various steady state parameters of hydrodynamic journal bearings have been determined to get maximum performance enhancement ratio. For…
Abstract
Purpose
The purpose of this paper is to provide the various steady state parameters of hydrodynamic journal bearings have been determined to get maximum performance enhancement ratio. For this, the bearings inner surface is textured with triangular shape with different texture depths and a number of textures in pressure increasing region. The textured region acts as a lubricant reservoir, which provides additional film-thickness and reduce friction. Therefore, enhance the overall performance of bearing.
Design/methodology/approach
In the present study, the effect of triangular shaped texture on the static performance characteristics of a hydrodynamic journal bearing has been studied. Different values of texture depths and a number of textures have been numerically simulated in pressure developing region. The static performance characteristics have been calculated by solving the fluid flow governing Reynolds equation using the finite element method, assuming iso-viscous Newtonian fluid. The performance enhancement ratio, which is the ratio of load carrying capacity (LCC) to the coefficient of friction (COF) has been calculated from results to finalized optimum design parameters.
Findings
The paper provides numerically obtained results indicate that surface texturing can improve bearing performance if the textured region is placed in the pressure increasing region. Moreover, surface texturing is the most effective at bearing performance enhancement when the bearing operates at lower eccentricity ratios and texture depth. The performance enhancement ratio, which is the ratio of LCC to the COF is found to be a maximum value of 2.198 at texture depth of 1.5, eccentricity ratio of 0.2 and the textured region located in the increasing pressure region.
Research limitations/implications
The present study is based on a numerical based research approach, which has its limitations. So, researchers are encouraged to investigate the same work experimentally.
Practical implications
The paper includes implications to be beneficial for designers for designing better hydrodynamic journal bearings.
Originality/value
For the triangular shaped texture, considered in the present study, the optimum values of texture depth and texture distribution region have also been determined. While designing, designers should focus on those values of texture depth, texture region and a number of textures, which give the maximum value of performance enhancement ratio, which represents maximum LCC at the lowest value of the COF.
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Hem Chander Garg and Vijay Kumar
The slot-entry hybrid journal bearings have been successfully used in various engineering applications because of their good performance over wide range of speed and load, besides…
Abstract
Purpose
The slot-entry hybrid journal bearings have been successfully used in various engineering applications because of their good performance over wide range of speed and load, besides their relative simplicity in manufacturing. Most of the research work pertaining to non-recessed journal bearing assumes standard symmetric and asymmetric configurations. However, many more configurations are possible by changing the position of slot which may improve the performance of the slot-entry journal bearing. In the present work study of static performance characteristics of slot-entry journal bearing of different configuration has been carried out. The paper aims to discuss these issues.
Design/methodology/approach
FEM has been used to solve the Reynolds equation governing the flow of lubricant in the bearing clearance space along with the restrictor flow equation. The non-Newtonian lubricant has been assumed to follow the cubic shear stress law. The performance characteristics of slot-entry hybrid journal bearings are computed by developing a computer program.
Findings
The simulated results of bearing characteristics parameters in terms of minimum fluid-film thickness and bearing flow have been presented for the wide range of various values of non-linearity factor and external load. It is found that there is an increase in the oil requirement for slot-entry hybrid journal bearing with the specified operating and geometric parameters, when the viscosity of the lubricant decreases due to the non-Newtonian behavior of the lubricant. The effect of the decrease in the viscosity of the lubricant due to non-Newtonian behavior of the lubricant diminishes the attitude angle. The computed performance characteristics are helpful for the bearing designer while choosing a particular configuration of bearing.
Research limitations/implications
The performance characteristics have been computed by considering the non-Newtonian lubricants. The thermal effects have been ignored in the analysis so as to obviate the mathematical complexity.
Originality/value
Get idea from already published manuscripts.
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H.C. Garg and Vijay Kumar
The changing technological scenario necessitated hybrid journal bearings to operate under severe conditions of heavy load and high speed resulting into temperature rise of the…
Abstract
Purpose
The changing technological scenario necessitated hybrid journal bearings to operate under severe conditions of heavy load and high speed resulting into temperature rise of the lubricant fluid-film and bearing surface. To predict the performance of a bearing realistically, theoretical model must consider the combined influence of the rise of temperature and non-Newtonian behavior of the lubricant. The aim of the present paper is to study the effect of viscosity variation due to temperature rise and non-Newtonian behavior of the lubricant on performance of constant flow valve compensated multiple hole-entry hybrid journal bearings.
Design/methodology/approach
Finite element method has been used to solve Reynolds equation along with restrictor flow equation, 3D energy equation and 3D conduction equation using suitable iterative technique. The non-Newtonian lubricant has been assumed to follow cubic shear stress law.
Findings
The thermohydrostatic rheological performances of symmetric and asymmetric hole-entry hybrid journal bearing configurations are studied. The computed results illustrate that variation of viscosity due to rise in temperature and non-Newtonian behavior of the lubricant affects the performance of hole-entry hybrid journal bearing system quite significantly.
Originality/value
In the present work, the influences of the viscosity variation due to temperature rise and non-Newtonian behavior of the lubricant on the performance characteristics of non-recessed hole-entry hybrid journal bearing with symmetric and asymmetric configurations compensated with constant flow valve restrictors have been investigated for generating the design data to be used by bearing designer. The design data computed in the present thesis are a contribution in field of knowledge of bearing design.
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R. Rashidi Meybodi, M. Zare Mehrjardi and A.D. Rahmatabadi
The purpose of this paper is to study tilt angle effects as design parameters of noncircular bearings, on the linear dynamic analyses of micropolar lubricated circular, two, three…
Abstract
Purpose
The purpose of this paper is to study tilt angle effects as design parameters of noncircular bearings, on the linear dynamic analyses of micropolar lubricated circular, two, three and four lobe journal bearings.
Design/methodology/approach
Reynolds equation in dynamic state is modified considering the micropolarity characteristics of lubricant, and it is solved using generalized differential quadrature method. The perturbed components of the dynamic pressure are extracted based on the linear dynamic model. To explain the transient state of the governing equation, through the linear dynamic approach, the whirling motion of rotor around the steady state position is assumed to be harmonic.
Findings
It is observed from the results that tilt angle has significant effects on the steady state and stability performance of lobed journal bearings. It may be selected suitably to improve the performance of rotor-bearing system, while all other lubricant properties and noncircular bearing design parameters are kept fixed. Results show that among the three types of bearings considered, the dynamic performance of two lobe bearings are more affected by the variation of tilt angle.
Originality/value
The present study is mainly concerned with the effects of tilt angle as a design parameter on the stability performance of a hydrodynamic noncircular journal bearing lubricated with micropolar fluid.
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Yangong Wu, Zheng Qiao, Jiadai Xue, Yutao Liu and Bo Wang
The purpose of this paper is to present a novel numerical approach to analyze the static performance of aerostatic thrust bearings by adopting a general finite element method…
Abstract
Purpose
The purpose of this paper is to present a novel numerical approach to analyze the static performance of aerostatic thrust bearings by adopting a general finite element method calculation program.
Design/methodology/approach
The characteristics of a gas film are described by the Reynolds equation and the pressure distribution is solved using the finite element method. A root iterative method is proposed to meet the requirement of the mass-conservation law because multiple pocketed orifice-type restrictors are treated as a series of special boundary conditions.
Findings
The static performance of a rotary table using aerostatic thrust bearings, including load carrying capacity and stiffness, can be predicted by the method; moreover, it can be further confirmed through experiments on the designed rotary table.
Originality/value
The method combining the finite element and root iterative methods is highly accurate and has a low time-cost for analyzing aerostatic thrust bearings with multiple pocketed orifice-type restrictors.
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Mojtaba Tahani, Mehran Masdari and Ali Bargestan
This paper aims to investigate the aerodynamic characteristics as well as static stability of wing-in-ground effect aircraft. The effect of geometrical characteristics, namely…
Abstract
Purpose
This paper aims to investigate the aerodynamic characteristics as well as static stability of wing-in-ground effect aircraft. The effect of geometrical characteristics, namely, twist angle, dihedral angle, sweep angle and taper ratio are examined.
Design/methodology/approach
A three-dimensional computational fluid dynamic code is developed to investigate the aerodynamic characteristics of the effect. The turbulent model is utilized for characterization of flow over wing surface.
Findings
The numerical results show that the maximum change of the drag coefficient depends on the angle of attack, twist angle and ground clearance, in a decreasing order. Also, it is found that the lift coefficient increases as the ground clearance, twist angle and dihedral angle decrease. On the other hand, the sweep angle does not have a significant effect on the lift coefficient for the considered wing section and Reynolds number. Also, as the aerodynamic characteristics increase, the taper ratio befits in trailing state.
Practical implications
To design an aircraft, the effect of each design parameter needs to be estimated. For this purpose, the sensitivity analysis is used. In this paper, the influence of all parameter against each other including ground clearance, angle of attack, twist angle, dihedral angle and sweep angle for the NACA 6409 are investigated.
Originality/value
As a summary, the contribution of this paper is to predict the aerodynamic performance for the cruise condition. In this study, the sensitivity of the design parameter on aerodynamic performance can be estimated and the effect of geometrical characteristics has been investigated in detail. Also, the best lift to drag coefficient for the NACA 6409 wing section specifies and two types of taper ratios in ground effect are compared.
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