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research-article

Rotor damped natural frequencies and stability under reduced oil supply flow rates

[+] Author and Article Information
Bradley Nichols

Rotating Machinery and Controls Laboratory, Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, 22904
brn7h@virginia.edu

Roger Fittro

Rotating Machinery and Controls Laboratory, Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, 22904
fittro@virginia.edu

Christopher Goyne

Rotating Machinery and Controls Laboratory, Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, 22904
goyne@virginia.edu

1Corresponding author.

ASME doi:10.1115/1.4040813 History: Received January 30, 2018; Revised June 29, 2018

Abstract

Reduced oil supply flow rates in fluid film bearings can cause cavitation, or lack of a fully-developed film layer, over one or more of the pads due to starvation. Reduced oil flow has the well-documented effects of higher bearing operating temperatures and decreased power loses; however, little experimental data is available on its effects on system stability and dynamic performance. The study looks at the effects of oil supply flow rate on dynamic bearing performance by comparing experimentally identified damped natural frequencies and damping ratios to predictive models. A test rig consisting of a flexible rotor and supported by two tilting pad bearings in flooded housings is utilized in this study. Tests are conducted over a range of supercritical operating speeds and bearing loads while systematically reducing the oil supply flow rates provided to the bearings. Shaft response is measured as a magnetic actuator is used to perform sine sweep excitations of the rotor. A single-input, multiple-output (SIMO) system identification technique is then used to obtain frequency response functions (FRFs) and modal parameters. All experimental results are compared to predicted results obtained from bearing models based on thermoelastohydrodynamic (TEHD) lubrication theory. Both flooded and starved model flow assumptions are considered and compared to the data. Differences in the predicted trends of the models and the experimental data across varying operating conditions are examined. Predicted pressure profiles and dynamic coefficients from the models are presented to help explain any differences in trends.

Copyright (c) 2018 by ASME
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