Transient Lift Off Testing Results for a Radial Hybrid Bearing
Abstract
An experimental test rig was designed and developed to test the performance of a hybrid bearing during its initial lift-off, referred to as start transient. The hybrid bearing studied was designed to replicate the geometry of the bearing used in a new Liquid Hydrogen Turbopump. The test rig uses a high-speed spindle motor capable of 20,000 RPM that drives a 782 Inconel rotor connected by a high speed flexible coupling. The rotor was supported by ceramic ball bearings on the coupling end, and the test hybrid bearing at the other end. A magnetic bearing is utilized to apply loads to the rotor at mid-span. During testing, several factors were varied including ramp rate (rpm/sec) to vary drive torque, supply pressure, applied loading, and load orientation to simulate various start transient scenarios. This data was analyzed in an attempt to quantify hydrodynamic and hydrostatic lift-off speeds. Hydrodynamic lift-off occurs when the rotational speed of the rotor causes the wedge effect of the film to overcome forces acting on the rotor, while hydrostatic lift-off occurs when the pressure (which is speed dependent) developed in the bearing overcomes the forces acting on the rotor to cause lift-off. The lift-off speed is an important quantity to determine for a certain condition to prevent rotor and bearing damage due to a prolonged rotor/bearing contact. With the rotor being loaded with a static force of 1X rotor weight in the vertical direction, it lifted-off hydrostatically at 4275 RPM. In the case of higher static vertical load, 8X rotor weight, it lifted-off hydrostatically at 7900 RPM. Testing showed that an increase in load and ramp rate increases the speed at which the rotor lifted-off. From this outcome, the hydrostatic lift-off is highly dependent on supply pressure and can be determined by graphical means. Although attempts were made to quantify hydrodynamic lift-off, the data showed no reliable indicators.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 2009
- Accession Number
- AD1007896
Entities
People
- Ralph H. Borchard
Organizations
- Air Force Research Laboratory