Tribology Transactions, 55: 798-804, 2012 Copyright C  Society of Tribologists and Lubrication Engineers ISSN: 1040-2004 print / 1547-397X online DOI: 10.1080/10402004.2012.711435 Effect of Ellipticity Ratio on the Performance of an Inverted Three-Lobe Pressure Dam Bearing N. K. BATRA, 1 GIAN BHUSHAN, 2 and N. P. MEHTA 1 1 Maharishi Markendeshwar Engineering College Ambala, Haryana, India 2 National Institute of Technology Kurukshetra, Haryana, India The ellipticity ratio is one of the major parameters that af- fect the performance of multilobe bearings. This article ana- lyzes the effect of ellipticity ratio on the performance of an in- verted three-lobe pressure dam bearing. The performance of an inverted three-lobe pressure dam bearing was found to be better than that of an inverted three-lobe bearing by incorpo- rating a pressure dam in the upper lobe and two relief tracks in the lower two lobes of an ordinary inverted three-lobe bearing. Evaluation of experimental work on ellipticity ratios was done in three steps, viz. 0.4, 0.5, and 0.6, and the results showed that the stability of an inverted three-lobe pressure dam bearing was increased with an increase in the value of the ellipticity ratio. KEY WORDS Inverted Three-Lobe Pressure Dam Bearing; Finite Element Method; Ellipticity Ratio INTRODUCTION The advanced development of modern engines and machin- ery has led to the increased use of bearings operating under high speeds and high pressures. The recent trends in designing very high-speed rotating machines result in making them compact and lightweight. It has been observed that the performance of ordi- nary circular bearings is not satisfactory at high speeds. To in- crease the stability of ordinary journal bearings, the use of multi- lobes and the incorporation of pressure dams are preferred. On the basis of analytical dynamic analysis (Nicholas and Al- laire (1), (2); Mehta and Singh (3)), cylindrical pressure dam bearings are found to be very stable compared to ordinary cylin- drical bearings. An experimental stability analysis of such types of bearings (Flack, et al. (4)) has shown that the analytical sta- bility analysis reflects the general trends in experimental data. The study of noncylindrical pressure dam bearings such as finite- elliptical, half-elliptical, offset-halves, and three-lobe and four- lobe pressure dam bearings proves that by incorporation of a pressure dam, the performance of bearings can be improved Manuscript received June 20, 2011 Manuscript accepted July 8, 2012 Review led by Gregory Kostrzewsky (Mehta, et al. (5)–(8); Mehta and Singh (9); Malik, et al. (10); Mehta and Rattan (11); Al Jughaiman and Childs (12)). Accord- ing to Sinhasan, et al. (13), the performance of an inverted three- lobe bearing is better than that of a three-lobe bearing. Because the incorporation of a pressure dam has proven to be useful in improving the stability of multilobe bearings, an inverted three- lobe pressure dam bearing is expected to be more stable than an ordinary inverted three-lobe bearing. The ellipticity ratio is one of the important factors affecting the performance of multilobe pressure dam bearings. Therefore, the present study has been un- dertaken to investigate the effect of the ellipticity ratio on the performance of an inverted three-lobe pressure dam bearing. BEARING GEOMETRY Figure 1 shows the geometry of an inverted three-lobe pres- sure dam bearing. A rectangular dam or step of depth S d and width L d was cut circumferentially in lobe 1 of the bearing. Cir- cumferential relief tracks or grooves of a certain depth and width L t were also cut centrally in lobes 2 and 3 of the bearing. Figure 2 shows lobe 1 with a pressure dam and lobes 2 and 3 with relief tracks. The relief tracks were assumed to be so deep that their hydrodynamic effects could be neglected. For a concentric position of the rotor, there were two refer- ence clearances of the bearing: a major clearance c given by a circle circumscribed by the lobe radius and a minor clearance c m given by an inscribed circle. Thus, the center of each lobe was shifted by a distance ep = c − c m known as the ellipticity of the bearing. The various eccentricities and ellipticities were nondi- mensionalized by dividing by the major clearance c. Ellipticity ratio (δ) = (c − c m ) /c = 1 − c m /c Eccentricity ratio (ε) = e/c ε 1 = e 1 /c, ε 2 = e 2 /c, ε 3 = e 3 /c If l 1 and l 2 are circumferential lengths of the bearing before and after the dam, l 1 = πRθ s /180 l 2 = πR (120 − θ s − 2θ g ) /180 798