THE EFFECTS OF SHAPE AND SIZE OF RECESSES ON THE PERFORMANCE OF COMPENSATED HYDROSTATIC JOURNAL BEARINGS USING FEM

Abstract

The multirecess compensated externally pressurized journal bearings are extensively used now-a-days viz, in machine tools industries, aerospace industries and test equipments etc. due to their high fluid film stiffness, low friction at very 'slow or zero speeds and good vibration damping. The performance of hydrostatic/hybrid-journal bearing systems• get affected by number of design parameters such as number of pockets, types of restrictor, bearing flexibility, fluid inertia bearing geometry and operating parameters, and type of operation of bearing (hydrostatic/hybrid), etc. It has been observed that the shape of recesses in most of the studies undertaken were rectangular and the studies related to other shapes of recesses i.e. square, circular, elliptical, triangular etc. have not been attempted so far. Therefore, the work includes the study of the performance of the multirecess compensated hydrostatic/hybrid journal bearing with different -shapes of recesses viz, square pocket, circular pocket, elliptical pocket and triangular pocket configurations. The performance of multirecesses compensated hydrostatic/hybrid journal bearing for different pocket configurations has been compared for the same bearing operating and geometric parameters and pocket area. For computing the bearing performance characteristics, the Reynolds equation for the flow of lubricant in the clearance with equation of flow through restrictor as a constraint has been solved using appropriate boundary conditions and iterative scheme. To accomlish this task a computer program based on finite element analysis has been developed. The flow field solution domain has been descritized using 4-noded two dimensional isoparameter elements. The developed finite element program based on the analysis used for solving flow field equations has been validated by undertaking several test cases. The static and , dynamic performance characteristics of multirecess compensated hydrostatic/hybrid journal bearing for various shapes of, recesses, has been presented in. graphical and tabular forms and logical conclusions about the effects of shapes and sizes of the recesses on the performance characteristics of journal bearings are drawn. It is observed that depending upon the desired performance, the particular bearing pocket configuration can be selected. Triangular pocket, bearing is observed to be suitable for only vitbration damping characteristics. But for good stiffness, circular pocket bearing can be selected, and elliptical pocket bering can be selected to be economical, from pu mng power point of view. Square pocket beaing is observed to performing with moderate performance characteristics.