A STUDY ON BEHAVIOUR OF HYDROSTATIC/HYBRID THRUST PAD BEARING CONFIGURATIONS

Abstract

Bearings are key elements of the power transmission system in machines and play an important role in their overall performance. A bearing is a machine element that permits desired constrained relative motion, restrains unwanted motion, and simultaneously supports external load. Bearings are used in a wide range of applications, from everyday household appliances to supporting both moving and stationary components in power plants, hydraulic pumps, automobiles, and telescopes. The reliability of machines/systems depends upon the proper and smooth functioning of bearing elements. Nowadays, machines are engineered to function under very demanding conditions characterized by heavy loads and high speeds. Performance of bearing is crucial, as energy loss due to friction and material wear results in significant economic costs and substantial environmental impacts. Over the years, greater attention has been paid to designing and developing energy-efficient high-load sustaining bearings. Hydrostatic/hybrid thrust pad bearing are generally used for supporting axial load in machines. These bearings are extremely important in machines, which often operate under heavy loads and relatively low sliding speeds. These bearings require many auxiliary elements, namely hydraulic valve restrictors, hydraulic pumps etc., which make the lubrication system rather complex and more involved. Nevertheless, unique advantages such as high load carrying capacity, low friction and wear (almost zero), high fluid film stiffness and damping coefficient etc., offered by these bearings substantially expand their range of industrial applications. Hydrostatic/hybrid thrust bearing found usage in applications ranging from small precision machines/equipment to supporting enormous turbomachines/structures such as rotors of hydraulic pumps and turbines, lock-gates, machine tools, observatory domes etc. Owing to the abovementioned advantages/features, researchers around the globe have focused their attention on analyzing, enhancing, and predicting the performance of hydrostatic/hybrid thrust bearing operating under stringent, exact, and precise operating conditions. In the analysis of hydrostatic/hybrid thrust pad bearings, it is assumed that bearing surfaces remain parallel during the normal operation of machines. However, in industrial and commercial applications, a certain degree of tilt is always present between the bearing surfaces due to manufacturing and assembly errors. Neglecting this tilt in the analysis may lead to inaccurate design data. Even a small tilt between the bearing surfaces can severely deteriorate the load-sustaining capability and fluid film stiffness characteristics of the bearings. Therefore, it is imperative to include the influence of tilt when numerically simulating the performance of hydrostatic/hybrid thrust pad bearings.