|dc.description.abstract||Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable
successful operation of oil-free microturbomachinery. This work presents the
experimental and analytical study of such bearings with different damper configurations.
A test rig was constructed that could safely operate a ~28.6 mm, 0.8 kg rotor beyond 120
krpm. A time domain orbit simulation, which integrates nonlinear equations of motion
for the rotor-bearing elements, was implemented as the primary analysis tool to predict
rotor-bearing responses to imbalance, the presence and location of critical speeds, etc.
Complementary analyses were also performed with a model that uses linear bearing
impedance coefficients to predict system natural frequencies.
Imbalance response testing verified that the rotor-bearing system behaved
linearly in the region above the critical speed, and orbit simulations predicted the
response to a calibrated imbalance with notable agreement. Viscoelastic dampers added
behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm
without damper to above 50 krpm with damper) of the system with bearing clearance
increased by shims. Midrange subsynchronous vibrations initiated at ~20 krpm were eventually suppressed by ~25 krpm due to the stabilizing effect of rotor centrifugal
growth. The viscoelastic dampers had a negligible effect on suppressing these midrange
subsynchronous vibrations in experiments, but this was not demonstrated in simulations,
presumably due to much lower stiffness contribution of the damper at lower frequencies.
The ideal, perfectly aligned models in the simulations were able to tolerate shims up to
only 10% of nominal clearance, but the test rig exhibited surprising stability with shims
as much as 200% of nominal clearance; this increase may be caused by imposed
eccentricities due to misalignments in the test rig.
FPTPGBs supported by compliant bump foils can have the ability to tolerate
rotor misalignments and shock loading like foil gas bearings. Simulation studies on
imbalance response characteristics for several bearing shell mass and support stiffness
configurations present initial design guidelines for the application. Namely, results
showed that FPTPGBs favored large bearing shell mass and large support stiffness,
while FPTPGBs with radial compliance favored small bearing shell mass with large