Abstract—In this paper, the dynamic characteristics of a three- lobe journal bearing lubricated with micropolar fluids are determined by the linear stability theory. Lubricating oil containing additives and contaminants is modelled as micropolar fluid. The modified Reynolds equation is obtained using the micropolar lubrication theory .The finite difference technique has been used to determine the solution of the modified Reynolds equation. The dynamic characteristics in terms of stiffness, damping coefficients, the critical mass and whirl ratio are determined for various values of size of material characteristic length and the coupling number. The computed results show that the three-lobe bearing lubricated with micropolar fluid exhibits better stability compared with that lubricated with Newtonian fluid. According to the results obtained, the effect of the parameter micropolar fluid is remarkable on the dynamic characteristics and stability of the three-lobe bearing. Keywords—Three-lobe bearings, Micropolar fluid, Dynamic characteristics, Stability analysis. I. INTRODUCTION DVANCES in technology and in many practical lubrication applications necessitate the development of improved lubricants where the Newtonian fluids constitutive approximation is not a satisfactory engineering approach to lubrication problems. The experimental results support the achievement of better lubricating effectiveness on blending small amount of long-chained additives with the Newtonian lubricants. Micropolar fluids obtained from the general microfluids by imposing the assumption of the skew symmetry of the gyration tensor and the microisotropic property are the simplest subclass of microfluids in which microstructure is still present [1]. A number of theories of the microcontinuum have been developed to explain the behavior of these fluids as polymeric fluids [2]. The study of the flow behaviours using the theory of micropolar lubrication was initiated with the problem of a two-dimensional slider bearing [3]. Shukla et al. [4] derived the generalized Reynolds equation for micropolar fluids with application to one- dimensional slider bearing. The infinitely long journal bearing lubricated with micropolar fluids was studied by PraKash et al. [5]. Singh and Sinha [6] made a detailed order of magnitude study and obtained the same form of Reynolds equation for the tree-dimensional case. Hauang et al. [7], [8] presented the static and dynamic characteristics of finite-width journal bearings lubricated with micropolar fluids. The effects of micropolar lubricants and three-dimensional irregularities in hydrodynamic journal bearings were studied by Lin [9]. Boualem Chetti is Faculty of sciences and technology, University of Khemis Miliana,Ain Defla, Algeria (e-mail: b.chetti@gmail.com). Das et al. [10] studied the effect of the misalignment on hydrodynamic journal bearing lubricated with a micropolar fluids. The dynamic characteristics of journal bearings lubricated with micropolar fluids were presented by Das et al. [11]. The current trend in the design of high-speed rotating machinery is to have a good dynamic stability. In such applications, multi-lobe bearings are often used because these have better dynamic stability than systems with plain journal bearings. The three-lobe bearing is a widely used non-circular bearing. In practical, all the lobes are manufactured with equal arc length. The theoretical analysis of three-lobe bearings was first presented by Pinkus [12]. The stability characteristics and general transient motion of a vertical three-lobe bearing were presented by Falkenhagen et al. [13]. The stability criteria for a multi-lobe bearing were developed by Lund et al. [14] based on linearization of the Reynolds equation by small perturbation theory. Sinhasan et al. [15] compared some three- lobe bearing configurations on the basis of the theoretical static and dynamic characteristics. The three-lobe bearing design data, which include both static and dynamic characteristics, were reported by Malik et al. [16]. Static and dynamic characteristics of 6 types of multi-lobe journal bearings in turbulent flow regime have been studied by Abdul- Wahed et al. [17]. Prabhu [18] made an investigation to evaluate the experimental performance of misaligned cylindrical and three-lobe journal bearings .A numerical procedure incorporating cavitation modeling in the predication of dynamic coefficients for four multi-lobe bearings is presented by Rao et al. [19]. Prabhkaran Nair et al. [20] presented an analysis of the deformation effect of the bearing liner on the static and dynamic characteristics of an elliptical journal bearing with a micropolar lubricant. Rahmatabadi et al. [21] studied the static characteristics of a noncircular journal bearing (two-lobe, three-lobe and four-lobe) lubricated with a micropolar fluids. In Recent investigation, Chetti [22] presented the effect of micropolar fluids on the dynamic characteristics of a four-lobe journal bearing. In the present work, dynamic characteristics in terms of stiffness, damping coefficients, the critical mass and whirl ratio are determined for a three-lobe journal bearing lubricated with a micropolar and Newton fluids. The effects of different values of micropolar parameter on the dynamic characteristics of the journal bearing are presented. II. MODIFIED REYNOLDS EQUATION Under the usual assumptions made for the lubrication film, the assumptions of the absence of body forces, body couples and constancy of characteristic coefficients across the film of Boualem Chetti Stability Analysis of Three-Lobe Journal Bearing Lubricated with a Micropolar Fluids A World Academy of Science, Engineering and Technology International Journal of Mechanical and Mechatronics Engineering Vol:8, No:12, 2014 1464 International Scholarly and Scientific Research & Innovation 8(12) 2014 scholar.waset.org/1307-6892/10000183 International Science Index, Mechanical and Mechatronics Engineering Vol:8, No:12, 2014 waset.org/Publication/10000183