A hybrid bearing designed for use in a next generation turbo-pump is evaluated
for the performance of initial lift-off, referred to as start-transient. The radial test rig
features a high-speed spindle motor capable of 20,000 rpm that drives a 718 Inconel rotor
attached via a high-speed coupling. The drive end is supported by ceramic ball bearings,
while the hybrid bearing supports the opposite end. A magnetic bearing delivers the
applied loading along the mid-span of the rotor. Many parameters, including ramp rate
[rpm/s] (drive torque), supply pressure at 15,000 rpm, magnitude of the applied load, and
load orientation, are varied to simulate different start-transient scenarios. The data are
recorded in .dat files for future evaluation of transient predictions.
Analysis of the data includes an evaluation of hydrodynamic and hydrostatic liftoff,
an assessment of rub from passing through a lightly damped critical speed, and
observation of pneumatic hammer instability. Hydrodynamic lift-off occurs when the
hydrodynamic pressure, resulting from the relative motion of two surfaces, overcomes
the forces acting on the rotor; no indication of hydrodynamic lift-off is provided.
Hydrostatic lift-off results from the external supply pressure (which for this test rig is
speed dependent) overcoming the forces acting on the rotor as determined from rotor
centerline plots. With 0.263 bar applied unit load in the vertical direction, hydrostatic
lift-off occurs at 0 rpm and 2.08 bar supply pressure. With a much higher load of 1.53
bar, hydrostatic lift-off is at 12,337 rpm and 10.7 bar supply pressure.
The required supply pressure for hydrostatic lift-off is approximately a linear
function of the applied unit load. In a turbopump, hydrostatic lift-off depends on the
speed because the supply pressure is proportional to the speed squared. With the load in the horizontal direction, hydrostatic lift-off occurs at lower speeds and pressures. The
ramp rate did not affect the required supply pressure for hydrostatic lift-off. A lower
supply pressure at 15,000 rpm lowered the required supply pressure for hydrostatic liftoff
as well as the natural frequencies creating a rub. The hydrostatic lift-off speed should
be minimized to avoid damage to the rotor/bearing surfaces due to contact.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-12-7444 |
| Date | 2009 December 1900 |
| Creators | Klooster, David |
| Contributors | Childs, Dara |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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