Transient Lift-Off Test Results for an Experimental Hybrid Bearing in Air

摘要

Turbo-pump applications that use ball bearings in cryogenic fluids can experience rapid wear when the pump is at full power, limiting the life of the bearing. Hybrid bearings have been proposed for use in next-generation turbo-pumps because of their Diameter X Speed (DN) life, low friction factor, and application in low-viscosity fluids. Hybrid bearings use an external pressure supplied through a flow restrictor (orifice) to create pressure that supports the rotor (shaft) without rotation. The pressure generated by the flow through an orifice gives the hybrid bearing a theoretical infinite DN life. The direct stiffness and load capacity of a hybrid bearing are independent of the fluid viscosity making a cryogenic application ideal. The cryogenic applications proposed for the next-generation of turbo-pumps utilize the pump-discharge fluid as the external pressure supplied to the bearing. Therefore, during start-up the bearings are flooded but unpressurized, at which point wear can occur due to rubbing between the rotor and the bearing. The time, speed, and supply pressure when rubbing during start-up ceases is referred to as 'lift- off'. Currently, there is a lack of available data to validate the theoretical predictions for the initial start-up, referred to as start-transient, of hybrid bearings. This report will present the transient lift-off results of a radial hybrid bearing with air as the supply medium, including the effects of varying the ramp rate (drive torque), the supply pressure at 15,000 rpm, the applied unit load, and load orientation.