Elsevier

Tribology International

Volume 97, May 2016, Pages 59-70
Tribology International

Combined influence of geometric imperfections and misalignment of journal on the performance of four pocket hybrid journal bearing

https://doi.org/10.1016/j.triboint.2015.12.049Get rights and content

Highlights

  • Geometric imperfections of journal.

  • Misalignment of journal.

  • Finite element analysis of 4 pocket hybrid journal bearing system.

  • MXZ causes more detrimental effect on the performance of bearing than MX or MZ.

Abstract

The present study investigates the effect of misalignment of journal in conjunction with the effect of geometric imperfections of journal on the performance of four pocket hybrid journal bearing system. Three types of geometric imperfections of journal viz. barrel shape, bellmouth type and undulated type are considered. The misalignment of the journal is incorporated in the analysis by using two parameters φ¯ and Ψ¯. The governing Reynolds equation is solved by using a Galerkin׳s technique. The numerically simulated results indicate that the performance of a journal bearing system gets significantly deteriorated due to the geometric imperfections and misalignment of journal.

Introduction

Modern manufacturing technologies have the capability to manufacture the machine components more accurately. Even though, it is rarely possible to manufacture the machine component without error. Likewise manufacturing processes of a journal and bearing may cause several geometric imperfections. The geometric imperfections of journal exhibit dynamic conditions while geometric imperfections of bearing exhibit static conditions as journal is rotating and bearing is fixed during the operation of journal bearing system. Hence to investigate the realistic performance of journal bearing system, geometric imperfections of journal are more important than geometric imperfections of bearing. The most common types of geometric imperfections of journal are barrel shape, bellmouth shape and circumferential undulations type. These geometric imperfections are of the order of fluid film thickness. Hence, these geometric imperfections of journal significantly contribute to alter the performance of a journal bearing system. That is why many researchers focused their attention to examine the effect of geometric imperfections of journal on the bearing performance [1], [2], [3], [4], [5], [6], [7], [8], [9]. Wilson [1] experimentally investigated the influence of geometry variations of journal on hydrodynamic bearing performance. Mokhtar et al. [2], [3] carried out the investigation to examine the influence of waviness of journal and bearing on the values of coefficient of friction and attitude angles and obtained a good agreement between theoretical and experimental results. Alderson and Webster [4] examined the effect of crankshaft lobing on the performance of connecting rod bearings. They observed that the value of minimum fluid film thickness may increase or decrease with increasing lobe amplitudes depending upon the relative position of a lobe peak or valley vis-à-vis the location of minimum fluid film thickness. Chennabasavan and Raman [5] theoretically investigated the effect of geometric imperfections of journal on the performance of porous hydrodynamic journal bearings. They considered different forms of geometric irregularities of journal such as barrel shape, bellmouth shape, circumferential undulations and a combination of bellmouth shape and surface undulations in their study. Recently, the influence of geometric imperfections of journal on the performance of multi recesses hydrostatic journal bearing was investigated in conjunction with the effect of micropolar lubricant [6], the effect of geometric shape of recess [7], the effect power lubricant [8] and the effect of turbulence [9]. The studies [1], [2], [3], [4], [5], [6], [7], [8], [9] reported that the influence of geometric imperfections of journal on the performance of journal bearing system is very significant. Therefore, it becomes imperative to consider these geometric imperfections of journal in the analysis to generate the more realistic, accurate and précised design data.

Further, practically it is very difficult to have ideal alignment of journal and bearing, i.e., there exists always some degree of journal misalignment. Non-central loading and shaft deflection due to elastic and thermal distortions may also results in the misalignment of journal. It may be realized that bearing gets failed in many situation due to misalignment. The misalignment in journal and bearing cannot be eliminated completely, however a little tolerance may be given to design to allow little misalignment of journal in bearing operation. Therefore, consideration of misalignment in the analysis of fluid film bearing system becomes quite important. In recent years a number of studies addressed this crucial issue and its influence on the bearing system [10], [11], [12], [13], [14], [15], [16], [17], [18], [19].

In the year 1922 Fisher [10] firstly observed that misalignment phenomenon significantly affects the axial flow at the bearing ends and causes an irregular heating of the bearing. In 1932, Mckee and Mckee [11] observed the fluid film pressure distribution in the axial direction caused by misalignment. In 1949, Buske and Rolli [12] noticed that the misalignment of journal results in a disturbance in axial symmetry of the fluid film pressure profile in the bearing. Later on, Dubois et al. [13] illustrated that the fluid film pressure profile of a misaligned bearing was not symmetrical. Later, they determined the values of shaft eccentricity at the ends of the bearing, axial flow rate and the local temperatures in the bearing [14]. They introduced a new parameter called the degree of misalignment to quantify the misalignment. Asanabe et al. [15] experimentally observed that misalignment significantly affects the fluid film pressure distribution and slightly modified the value of coefficient of friction. Singh et al. [16] demonstrated that the misalignment of journal distorts the symmetry of pressure contours about journal mid-plane, reduces the maximum fluid film pressure, load carrying capacity and increase the friction coefficient resulting in an increase in power loss in the system. Sato and Ogiso [17] They noticed that the misalignment of journal results in a reduction in the values of stiffness as well as the load carrying capacity.

Bou-Said and Nicolas [18] examined the influence of misalignment on static and dynamic characteristics of hybrid bearings in laminar and turbulent regimes. They reported that the misalignment enhances the recess flow and reduces the recess pressure. The influence of misalignment for turbulent flow was lesser than that for laminar flow. Andres [19] studied the effect of misalignment on rotor dynamic coefficients of a hydrostatic journal bearing with end seals. They noticed that the direct and cross-coupled moment stiffness coefficients increases with an increase in journal speed whereas the direct moment damping coefficients remains unaffected. Andres [20] discussed the effects of static misalignment angles on the performance of a water lubricated five recess hydrostatic journal bearing. Qiu and Tieu [21] studied the effect of journal misalignment on the static and dynamic performance characteristics of a horizontally grooved journal bearing system. For the same value of external load, the misaligned bearing was observed to be more stable than the aligned bearing.

Prabhu [22] experimentally investigated the influence of misalignment on the performances of circular and 3-lobe journal bearings. This work was extended by Arumugam et al. [23], who investigated the dynamic characteristics of the cylindrical and 3-lobe journal bearings. It was observed that the misalignment in horizontal direction results in an increase in the value of fluid film stiffness coefficient in the vertical direction and a reduction in the value of fluid film stiffness coefficient in the horizontal direction. Sharma et al. [24] theoretically studied the journal misalignment effect on the static and dynamic performance of a capillary compensated hole-entry hybrid journal bearing. Osman [25] used finite difference method to examine the influence of misalignment on the performance of hydrodynamic journal bearings lubricated by non-Newtonian ferrofluid.

Bouyer and Fillon [26] experimentally observed that for the largest value of misalignment torque, the maximum fluid film pressure in the mid plane decreased by 20% while the minimum fluid film thickness was reduced by 80%. Later on, they carried out a theoretical study [27] to improve the performance of misaligned journal bearing by adding either local or global defect to the bearing geometry. Recently, Sharma et al. investigated the effect of misalignment of journal on the performance of hydrostatic journal bearing system in conjunction with the effect of surface roughness and non-Newtonian lubricant [28], with the effect of micropolar lubricant [29] and the effect of wear [30].

A thorough review of the literature pertaining the influence of geometric imperfections of journal on the bearing performance clearly reveals that the presence of geometric imperfections of journal significantly affects the performance of journal bearing system. Therefore, consideration of geometric imperfections of journal in the analysis is very important for the generation accurate design data. Further, the misalignment of journal is also a usual problem that causes a degradation in the performance of bearing system. To the best knowledge of author(s), no comprehensive study pertaining the combined influence of geometric imperfections of journal and misalignment of journal is available in the published literature. Therefore, the present study is planned to address this gap in literature and examines the influence of geometrically imperfect misaligned journal on the performance of CFV (constant flow valve) restricted four pocket hybrid journal bearing. Finite element method is used to solve the governing Reynolds equation. The numerically simulated results indicate that the geometric imperfection of journal and misalignment of journal significantly affect the performance of bearing system. The results of the study are expected to be quite useful for the bearing designers and researchers.

Section snippets

Analysis

The Reynolds equation governing the flow of incompressible, isoviscous flow of Newtonian lubricant in a finite length hydrostatic journal bearing Fig. 1 is expressed in non-dimensional form as follows [6], [7], [18], [19].α[h¯312p¯α]+β[h¯312p¯β]=Ω2h¯α+h¯t¯

Solution scheme

In order to establish the pressure field {p¯}, the governing algebraic Eq. (4) is solved incorporating the appropriate boundary conditions as given in Section 2.3. Fig. 4 depicts the block diagram illustrating the solution procedure adopted in the present study to determine the unknown fluid film pressure and desired performance characteristics parameters. In block LDATA, the bearing geometric and operating parameters are fed as input. In FTHIK module, the fluid film thickness is computed for

Results and discussion

On the basis of the solution procedure illustrated in Fig. 4, a computer program has been developed to compute the unknown pressure field and thereby performance characteristics parameters. In order to authenticate the methodology adopted, the results of a CFV compensated ideal journal bearing operating in aligned conditions have been compared with previously published results [32]. Fig. 5 depicts a close agreement of present results with already published results.

To simulate the performance of

Conclusions

A numerical study to examine the combined influence of geometric imperfections and the misalignment of journal on the performance of CFV compensated four pocket hybrid journal bearing system has been carried out. The following conclusions have been drawn on the basis of numerically simulated results.

  • 1.

    Different forms of geometric imperfection of journal generally results in a reduction in the value of h¯min. Further, misalignment of journal may cause a significant reduction in the value of h¯min

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