Aerodynamic analysis of compliant journal foil bearings

Abstract

This thesis provides a detailed study about the aerodynamic analysis of compliant journal foil bearings. In high speed turbomachinery elements, conventional bearings can’t be used since at such a high speed (50000-80000) rpm these bearings get worn and thus they fail. In this project the analysis of a compliant bearing, which has bump foils to enhance the load carrying capacity, has been done. The thin air film between the rotating shaft and the bearing creates the pressure to support the load. Reynolds Equation was first devised for the given compliance system. Due to its nonlinear nature iterative methods are required to solve it. For calculating the pressure distribution and hence the load carrying capacity of the bearings Finite Difference Approximations were used and a unique method, method of quadratic equations was used to find out several parameters. Using MATLAB several codes have been written to find out the pressure profile and the minimum film thickness whose 3 dimensional graphs have been plotted. After the pressure profile has been generated the load carrying capacity has been evaluated for the bearing under the given input parameters. Thereafter several comparisons have been made between the foil and the rigid bearing on the basis of the plots. Finally two different materials, one used for high temperature applications-Inconel X-750 and another used for low temperature applications Aluminium Bronze have been compared to find out their compatibility in different commercial applications based on their load carrying capacity.