Analysis of a Gas Lubricated Hydrodynamic Thrust Bearing

Abstract

Experimental results from a gas thrust bearing test facility are reported in this paper. This fundamental investigation of the thermo-fluid dynamics of a gas lubricated bearing forms part of a wider programme aimed at their introduction into the aeroengine environment. The experiments provide the most detailed measurements to date of a hydrodynamic lubrication film which uses gas as a working fluid. The bearing tested was lubricated with air. The thrust pads had an outer radius of 0.125 m and during operation the clearance between the bearing surfaces was typically 10 μm. The design speed of the bearing was 10,000 rpm. Mean pad pressure and temperature distributions are presented for a range of bearing loads up to 3/4 kN, which were measured under steady operating conditions. Transient pressure and surface clearance measurements from fast response probes are also reported. These measurements show a complex relative motion of the bearing surfaces, the exact nature of which could only be determined from a more detailed set of surface clearance measurements than those in the present work. However, the transient pressure measurements show that these surface clearance fluctuations do not exert a strong influence on the lubrication film pressures, which can be considered to be essentially steady. The test data are compared with predictions obtained by solving Reynolds equation numerically, using a finite-volume based procedure. Thermal distortion of the bearing surface is not included in the model and this limits the agreement between measurements and calculations. The results suggest that this must be accounted for in the design of practical bearing systems, even though the lubrication film can be treated as isothermal. The measurements also show evidence of the inlet effects which raise the static pressure of the flow entering the bearing to above the ambient level.