COMBINED INFLUENCE OF WEAR ON THE PERFIR NCE OF 2-LOBE _ SIX-POCKET HYBRID JOURNAL'' ARINQ SYSTEM IN TURBULENCE REGIME

Abstract

In recent times Hydrostatic/Hybrid Journal bearings have received consi e amount~fi attention by the researchers of their excellent performance as co erred to other class of bearings. Hydrostatic/Hybrid journal bearing has increased in the number of engineering applications such as machine tools, test equipment, medical equipment, measuring instruments, optical telescopes and aerospace industry etc. due to their ability to support heavy loads at low speeds, low frictional characteristics and good vibration damping characteristics. The main problems associated with the circular fluid film journal bearings are poor stability characteristics and self excited vibrations. Circular journal bearings are known to be prone to vibrations and frequently exhibit a kind of instability known as whirl or whip at high speeds. Under these circumstances, as well as rotating in the usual manner, the journal begins to wobble or whirl around in the clearance space of the bearing with, the centre of the journal at some eccentric distance from the centre of the bearing. If the conditions worsen, the amplitude of whirling becomes large and that may result in the destruction of the shaft and the bearing. i.e. failure-inducing instability. In order to improve the bearing stability, various non circular journal bearing configuration have been developed by researchers to eliminate or control whipping. The Non-circular bearings are quite frequently used in high speed machinery as they are efficient and less costly and provide better shaft stability. The Two-lobe bearing (elliptical bearing) are among the commonly used non-circular bearing configuration. A 2-Lobe Six-Pocket hybrid journal bearings have been developed to combine the features of non-circular and circular hybrid journal bearing configurations. Generally, in the partial lubrication regime, rubbing of asperities causes wear. The wear mechanisms by which the asperity material is removed, varies considerably with the asperity. geometry, surface film shear stress, material property and lubricant chemistry. For example, the asperity with random geometry generally results in abrasive wear in -which material is removed by ploughing or cutting. The field of wear is very broad; the present study is basically concerned with the wear. The performance of hydrostatic/hybrid journal bearing systems gets affected by number of parameters such as restrictors, bearing liner flexibility and mode of operation of bearing (hydrostatic/hybrid) etc. Therefore, the present work is aimed to study the effect of wear on the ii performance of the bearing operating in turbulent regime. When the journal bearins — ..item is subjected to heavy loads, the bearing linear deforms under high fluid film pressurtnis »-n modifies the fluid film thickness profile and ultimately changes bearingmance. For computing bearing performance characteristics, the Reynolds equation for the flow of lubricant in the clearance space with equation of flow through restrictor as a constraint has been solved using appropriate boundary conditions. The flow field solution domain has been discretized using 4-noded isoparametric elements. The static and dynamic performance characteristics are presented for various effects and conclusions are drawn. The study reveals that the overall decision regarding how the bearing performance due to wear and turbulent effect on the basis of stiffness, minimum fluid film thickness and threshold speed etc. has been drawn. iii