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A Test Rig to Measure the Static Load Performance of a Water Lubricated Thrust Bearing
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A thrust bearing test rig experienced a catastrophic failure while operating with gas bearings. After many repairs, the test rig is in operating condition with water-lubricated bearings. Previous work details the failure and several initial repairs and modifications. Further modifications include manufacturing two rotors, repairing the main housing, aligning the motor shaft and test rotor, upgrading the water pipeline system, developing a static load system, installing instrumentation, and developing means of data acquisition. Presently, the revamped system has rotated to a speed of 5 krpm. Measurements of the free-free mode natural frequencies and lateral mode shapes of the rotor-coupling system show that the rotor and quill shaft operate as a unit. Once assembled, water lubricates the bearings to lift and support the test rotor connected to the motor through its coupling. Impact loads identify the system fundamental natural frequency and damping ratio for operation without rotor speed or active thrust bearings. The flexibility of the quill shaft commands the location of the system lateral natural frequency (~ 93 Hz) and its low damping ratio. XLTRC2® based predictions agree well with the measured natural frequency and identified damping ratio. The water lubricates the radial bearings to lift the test rotor again as the motor accelerates the rotor to 5 krpm. During this operation, the rotor motion is synchronous and does not excite the first natural frequency. While operating at speeds up to 5 krpm, the system did not reach its first critical speed. Measurements show the thrust bearing axial clearance increases as the water supply pressure increases, max. 4.14 bar(g), for operation with a constant axial load and at null or low rotor speed (3 krpm). As the imposed axial load increases, the operating clearance decreases exponentially. The decreasing operating clearance causes an increased flow resistance across the film lands, resulting in a reduced flow rate. As the flow rate decreases, there is a lower pressure drop across each orifice, resulting in an increase in recess pressure. The derived axial stiffness increases as the axial clearance decreases or the water supply pressure increases. XLHydroThrust® uses the thrust bearing geometry to generate predictions of thrust bearing performance. The predictions accurately describe the influence of the load and supply pressure on the thrust bearing performance; however, there are discrepancies between the magnitudes of the predictions and the magnitudes of the measurements at a high axial load (low axial clearance). The average percent difference between the predicted and measured magnitudes of supply flow rate, flow rate through inner diameter, axial clearance, and recess pressure ratio change from 2% to 47%, 7% to 73%, 25% to 53%, and 7% to 18%, respectively, as the applied axial load increases from its minimum to maximum magnitude. Thus, there is a significant increase in difference between the predicted and measured magnitudes as the applied axial load increases. Future work includes measurements of static and dynamic load performance of a water lubricated hybrid thrust bearing.
Rohmer, Michael A (2015). A Test Rig to Measure the Static Load Performance of a Water Lubricated Thrust Bearing. Master's thesis, Texas A & M University. Available electronically from