Novel technique for the experimental determination of bearing and windage losses in an axial flow compressor

This paper describes an experimental technique for the determination of bearing and windage losses in an axial flow compressor. These losses must be accurately known when the isentropic efficiency of the compressor is calculated on the basis of the input torque. In the novel technique described here, even in the absence of the normal air compression process (i.e. without blades), the same magnitude of axial and radial loads are produced on the bearings, thereby simulating the actual operating conditions of the bearings. This is achieved by replacing the compressor disc and blades by an equivalent plain disc, and admitting pressurised air on one face of this plain disc to provide the required axial thrust. Using this new experimental technique the bearing and windage losses in an axial compressor stage were accurately determined for different speed and load conditions. The inadequacies of the theoretical methods for the estimation of these losses are pointed out. The method of incorporating the experimentally determined values of the losses in efficiency calculations is indicated