Effect of side feed pressurization on the dynamic performance of gas foil bearings
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abstract
Oil-free micro turbomachinery implementing gas foil bearings (GFBs) has improved mechanical efficiency and reliability. Adequate thermal management for operation in high temperature environments is an issue of importance in applications such as in gas turbines and turbochargers. GFBs often need a cooling gas flow, axially fed through one end of the bearing, to transport the heat conducted from a hot turbine, for example. Side gas pressurization, however, has a paramount effect on reducing amplitudes of motion, synchronous and subsynchronous. Presently, shaft motion measurements in a test rotor supported on GFBs show this remarkable effect. A computational gas film model implementing the evolution of gas circumferential flow velocity as a function of the imposed side pressure is advanced. Predicted direct stiffnesses and damping coefficients for the test GFB increase as the magnitude of feed pressure raises, while the difference in cross-coupled stiffnesses, directly related to rotor-bearing system stability, decreases. Predictions of threshold speed of instability and whirl frequency ratio are in close agreement with the measurements.
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ASME/STLE 2007 International Joint Tribology Conference, Parts A and B
