Experimental Determination of the Distributed Dynamic Coefficients for a Hydrodynamic Fluid Film Bearing

Open Access
Author:
Gyurko, John Harrison
Graduate Program:
Acoustics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 04, 2013
Committee Members:
  • Stephen A Hambric, Committee Chair/Co-Chair
  • Karl Martin Reichard, Committee Chair/Co-Chair
  • Eric Russell Marsh, Committee Member
  • Martin Wesley Trethewey, Committee Member
Keywords:
  • hydrodynamic lubrication
  • experimental test rig
  • fluid film bearing
  • dynamic bearing coefficients
  • circumferential distribution
Abstract:
Most current rotor bearing analysis utilizes lumped parameter bearing coefficients to model the static and dynamic characteristics of fluid film bearings. By treating the stiffness and damping properties of the fluid film as acting upon the axial centerline of the rotor, these models are limited in their analysis to first order lateral rotor-bearing motion. The development of numerical methods that distribute the dynamic properties of the fluid film around the bearing circumference allow for higher order analysis of the motion between the bearing and rotor. Assessment of the accuracy of the numerical method used to calculate distributed dynamic fluid film bearing coefficients is performed by developing a novel hydrodynamic journal bearing test rig and experimental testing procedure capable of obtaining measured distributed dynamic coefficients over a range of bearing operating conditions. The instrumented bearing test rig is used to measure the dynamic bearing displacement and fluid film pressure responses from application of an externally applied excitation force. Least squares solution to a system of perturbated pressure equations, populated by measured displacement and pressure responses, is used to determine the hydrodynamic stiffness and damping properties for a finite region of the bearing surface. Incremental rotation of pressure sensors embedded in the body of the test bearing allow for measurement of the fluid film circumferential pressure distribution which is used to calculate a set of experimentally determined dynamic bearing coefficients. Distributed bearing coefficients derived from experimental measurements are compared to numerically calculated distributed coefficients as well as to lumped parameter coefficients generated from experimental and numerical methods found in the literature. Overall, the numerically calculated distributed coefficients successfully model both the circumferential distribution and the operating conditions of the experimental distributed bearing coefficient values and show reasonable correlation to results obtained through lumped parameter methods. Excitation frequency independence is validated through experimental testing over multiple frequencies, and damping cross term inequality of the numerically distributed bearing coefficients is validated by lumped coefficient analysis found in the literature. While uncertainty and variation of the test rig dimensional and operating parameters have some effect on the accuracy with which the numerical methods model the experimental results, the most significant source of dissimilarity in numerical and experimental results comes from test rig specific features not captured in the numerical methods, such as bearing surface wear and bearing-shaft misalignment.