Tests are performed on a flexure-pivot-pad tilting-pad bearing with a series integral squeeze film damper in load-between-pads configuration, with both active and locked damper. The damper effects are negated when locked, resulting in a flexure-pivot-pad bearing only. Experimental tests provide static performance data and dynamic stiffnesses from which rotordynamic coefficients are extracted. The following two excitation schemes are implemented: (1) multi-frequency, single direction excitation and (2) single-frequency, rotating load excitation (or "circular excitation"). The XLTRC2 Rotordynamics Software Suite provides stiffness and damping coefficient, eccentricity, and power loss predictions for the locked damper bearing. Test conditions include the rotor-speed range of 4000-12000 rpm and the unit-load range of 0-862 kPa (0-125 psi). Dynamic tests utilizing the multi-frequency excitation for the locked and active damper bearing configurations both show that the real portion of the dynamic stiffness is well modeled by a quadratic curve fit, and the imaginary portion representing the damping is a linear function of excitation frequency. This means that frequency independent coefficients can be obtained when an added mass term is included. While stiffness coefficients are lower for the active damper bearing, damping coefficients remain almost constant between the locked and active damper configurations. A simulation shows that, although the damping coefficients do not change significantly, the reduced stiffness provided by the damper results in greater effective damping. Static performance tests for the locked and active damper bearing indicate low cross-coupling, as shown by the eccentricity and low attitude angle measurements. Pad metal temperature measurements show a smaller temperature differential along the pad arcs for the active damper bearing, than observed for the locked damper case. Frictional power loss is estimated based on lubricant temperature rise and does not differ significantly for the two bearing configurations.

This thesis presents the dynamic and static forced performance of a flexure-pivot tilting-pad bearing load between pad (LBP) configuration for different rotor speeds and bearing unit loadings. The bearing has the following design parameters: 4 pads with pad arc angle 72o and 50% pivot offset, pad axial length 0.0762 m (3 in), pad radial clearance 0.254 mm (0.010 in), bearing radial clearance 0.1905 mm (0.0075 in), preload 0.25 and shaft nominal diameter of 0.11684 m (4.600 in). The dynamic coefficients and the static performance parameters of the FPB have been compared with the theoretical predictions using the isothermal analysis from the rotordynamic software suite XLTRC2-XLTFPBrg. The bearing shows a small attitude angle, about 10o, which indicates small crosscoupling stiffnesses. The pad temperatures increase in the circumferential direction of rotation with speed and load. The pads maximum temperature was measured near the trailing edge. The dependency of the stiffness and damping coefficients on the excitation frequency has been studied. The frequency dependency in the dynamic coefficients was removed by introducing an added mass coefficient to the bearing model. The direct added mass coefficients were around 32 kg. The direct stiffness and damping coefficients increase with load, while increasing and decreasing with rotor speed, respectively. A small whirl frequency ratio (WFR) was found of about 0.15, and it decreases with load and increases with speed. A comparison between the dynamic stiffnesses using a Reynolds equation and the bulk-flow Navier-Stokes models with the experimental dynamic stiffnesses shows that the Reynolds model (even for laminar flows) is not adequate, and that the bulk-flow model should be used for rotordynamic coefficients prediction. The bulk-flow model in general predicts well the static performance parameters and the direct dynamic coefficients, and underpredicts the cross-coupled coefficients (overpredicts the stability).