Experimental and theoretical investigations of the dynamic properties for tilting-pad journal bearings

Abstract

Rotors of high-speed machinery are usually supported in tilting-pad journal bearings (TPJB), which offer inherent stability resulting from theoretically zero cross coupling dynamic coefficients. The rotordynamic analysis is usually based on linear bearing stiffness and damping coefficients calculated after ignoring pad mass and assuming synchronous shaft vibration (synchronously reduced coefficients). Measurement of the bearing dynamic properties has been a challenge for many years. This is particularly true for TPJB, which demonstrate a certain dependence on frequency of excitation. The paper presents theoretical and experimental evaluation techniques for stiffness and damping coefficients of TPJB. Some results are also shown. The theoretical results have been obtained from a computer model, which accounts for thermal and elastic effects, including those of pivot flexibility. Experimentally, the dynamic coefficients have been evaluated from the measured excitation force, acceleration and bearing/shaft displacement using a power spectral density technique. The experimental investigations have been supplemented by uncertainty considerations for the frequency domain method. These considerations have been based on analysis of propagation of elemental errors associated with the measurements of displacement and acceleration. The results illustrate the effects of pivot flexibility on the bearing stiffness and damping properties and their variations with frequency.

Keywords:

• Rotating machinery
• hydrodynamic bearing
• tilting-pad journal bearing
• bearing dynamics
• linear dynamic coeffi cients
• power spectral density technique
• uncertainty analysis
• error propagation

Additional information

Notes on contributors

W Dmochowski

Dr Waldemar Dmochowski is leader of the Tribology Group in the Gas Turbine Laboratory of the Institute for Aerospace Research at the National Research Council Canada. His major research interests are in the area of tribology, in particular fluid film lubrication and bearing dynamics.

Waldemar studied mechanical engineering at the Technical University of Gdansk, Poland. After receiving his MSc, he worked at the Institute of Fluid Flow Machinery, Polish Academy of Sciences in Gdansk, where he received his PhD. In 1987 he joined the National Research Council Canada and continued research in tribology, in particular on testing and modeling of the journal bearings performance.

He is the author of more than 100 technical papers and reports on fluid film lubrication and related topics.