Comparison Between Predictions and Measurements of Performance Characteristics for an Eight Pocket Hybrid (Combination Hydrostatic and Hydrodynamic) Thrust Bearing
Technical Report,03 Dec 2008,10 Feb 2015
AFRL/RQRC Edwards AFB United States
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A test rig was designed, produced, and used to test a hybrid thrust bearing geometry. The rig uses a hydraulic cylinder to load axially the rotor system supported by hybrid journal and thrust bearing supports. Two identical thrust bearings react the static axial load via two fluid films loaded against collars of the test rotor. The hybrid thrust bearing has an outer radius of 38.1 mm and an inner radius of 20.32 mm. The bearing has eight pockets spaced evenly at the mid-radius with a supply orifice located in the center of each pocket. The hybrid thrust bearing was tested at 3.45, 10.34, and 17.24 bar supply pressure with water operating at three rotor speeds of 7.5, 12.5, and 17.5 krpm. Each test thrust bearing inlet supply-pressure condition was tested with at least eight loads spanning the load range predicted by XLHydroTHRUST registered trademark. The report details XLHydroTHRUST registered trademark prediction validation against measurements of the performance characteristics of the turbulent hybrid thrust bearing. Predictions correlate reasonably well for flow rates especially for the 17.24 bar supply pressure condition. Additionally, measurements of flow rate through the inner radius of the test thrust evidences the onset of starvation sub-ambient pressures of the fluid film across the land for a high-speed 17.5 krpm and low-load condition due to fluid centrifugal acceleration. Predictions correlate reasonably well for load capacity especially for higher loads small film thickness. Also, measurements of the performance characteristics of the turbulent hybrid thrust bearing with rotor spinning were compared to those measured by Forsberg without speed. The comparison between the two sets of static measurements show good agreement for test case average clearances equal and greater than the nominal clearance of 76.2 micrometers low to mid loading.