Experimental Investigation of Structural Characteristics and Viscous Energy Dissipation in Multiple Cantilever Gas Foil Radial Bearings

Gas foil bearings are self-lubricating aerodynamic bearings which offer a low-cost alternative to traditional hydrodynamic oil bearings. In this work, static stiffness and viscous dissipation are established experimentally for cantilevered radial gas foil bearing. To establish dry frictional torque, running torque and touch-down torque, a low-speed test rig is built that can reach a maximum of 30k rpm. Static load-deflection curves for various foil bearings showed that increased preload shows the non-linear behaviour of stiffness which might be necessary for rotor stability. Tests also showed good capacity of mechanical energy dissipation by the cantilever foil. However increased preload resulted in higher dry sliding frictional torque. A linear increase in the dry sliding frictional torque is observed by increasing the specific load from 8.29kPa to 30.2kPa. On the other hand, the dry-sliding friction coefficient derived from the measured drag torque decreases rapidly with an increase in the net-specific load. Subsequently, drag torque tests were conducted at a rotor speed of 30 krpm with increasing net-specific loads. In each test, the recorded drag torque showed two sharp peaks during the rotor acceleration (start-up) and deceleration (shutdown) periods. The measurements revealed a linear increase in the amplitude of these two peaks with an increase in the net-specific load.