Tribology International

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A numerical investigation of both thermal and texturing surface effects on the journal bearings static characteristics

Nacer Tala-Ighil

^a,n

, Michel Fillon

^b

aWelding and NDT Research Center (CSC), BP 64 Cheraga, Algiers, Algeria

bInstiute Pprime, CNRS, University of Poitiers, ENSMA, Poitiers, France

a r t i c l e i n f o

Article history:

Received 16 July 2014 Received in revised form 4 February 2015 Accepted 13 February 2015 Available online 28 April 2015 Keywords:

Journal bearings Hydrodynamic lubrication Stribeck curve

Texture

a b s t r a c t

Journal bearing characteristics modellization has been investigated in this paper for both cases of texture presence or absence onto the bearing surface. The thermal effect has been studied. The used numerical approach in this analysis isﬁnite difference method. The textured bearing performance enhancement passes essentially by a minimum ﬁlm thickness and a friction torque improvement through an appropriate surface texture geometry and right texture distribution on the bearing surface. It is found that the simulations results are in good concordance with those issued from the literature. The obtained results by considering the temperature effect are more realistic.

1. Introduction

Nowadays, there is a strong need to make machines more efﬁcient by looking for power losses and trying to reduce them.

The most important losses in a machine come from the bearings [1]. These bearings are widely used in industries because of their simplicity, efficiency, and low cost. A lubricant separates the surfaces and hence reduces the frictional force, which leads to wear. These bearings have several advantages such as low friction and wear, good heat dissipation through the oil and noise and vibrations reduction. Their lubrication is really important due to the fact that the contact between surfaces would cause rapid wear [2]. The use of the Reynolds equation for the fluid pressure is rigorously justified as the asymptotic limit of Stokes equations under thin film hypothesis. In order to take into account the possible cavitation phenomena, which may lead to the rupture of thefluidfilm, the pressure lubricant behavior is governed by the Reynolds cavitation boundary conditions that prevent the emer- gence of non-physical negative values. The bearing temperature field and pressurefield are considerably influenced by the journal bearing parameters [3]. With large temperature variations, a thermal model must be used, as large changes in the lubricant viscosity occur. The average temperature is evaluated by using a very simple hypothesis.

The deterministic roughness that is known as surface texture was introduced deliberately on the bearings by using micro- fabrication techniques. Surface texturing is claiming progressively more attention and is expected to be a major component in future bearing structure design as demonstrated by the authors[4,5].

Patterned or artificially textured surfaces have been studied extensively for many applications, particularly in rotating machin- ery[6,7]. However, it was only recently that been such textures engineered in order to improve the machine elements tribological performance [8,9]. Microtextures act as micro-hydrodynamic bearings, enhance load support and increasefilm thickness, which leads to lower friction compared to untextured surfaces. Lu and Khonsari[10]have presented experimental results concerning the dimples effect on the Stribeck curve. Load, oil type, dimple size, depth and shape were varied to explore their influence on the friction characteristics. The new technologies as chemical etching [10], laser surface texturing[11]and novel dressing technique[12]

currently permit to create controlled micro-geometries (dimples or textures) on journal bearing surfaces. Surfaces texturing is expected to improve the general tribological performance includ- ing the friction reduction, the reliability improvement, the severity conditions increase, and the energy consumption lowering. Some other and recent studies[13–19]have established that the surface texture geometry such as dimple depth, width, dimple number, and dimple location inﬂuence the bearing performance.

The solution for the exactﬁnite-length bearing can be calcu- lated by solving the two-dimensional Reynolds equation, using the ﬁnite-difference method. Most of the methods used to solve this equation are based on the Reynolds cavitation boundary Contents lists available atScienceDirect

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nCorresponding author.

E-mail address:n.tala-ighil@csc.dz(N. Tala-Ighil).

Tribology International 90 (2015) 228–239