Adjustable ETHD lubrication applied to the improvement of dynamic performance of flexible rotors supported by active TPJB

This paper reports the dynamic study of a flexible rotor-bearing test rig which resembles a large overhung centrifugal compressor. The rotor is supported by an active tilting pad journal bearing (TPJB) able to perform the adjustable lubrication regime. Such a regime is obtained by injecting pressurized oil directly into the bearing clearance through a nozzle placed in a radial bore at the middle of the pad and connected to a high pressure supply unit by servovalves. The theoretical model is based on a finite element model, where the active TPJB with adjustable lubrication is included using the full dynamic coefficients matrices obtained by an Elasto-Thermo-Hydrodynamic (ETHD) model of the TPJB. Theoretical results are presented in Campbell diagram, stability map, mode shapes and frequency response functions (FRFs). The experimental FRFs and the modal parameters of the test rig are also obtained and compared against the theoretical results. The main contribution of this work is to present theoretically and experimentally the feasibility of modifying the dynamic performance of the test rig by means of the adjustable ETHD lubrication. Fair agreements between the theoretical and the experimental results are obtained. The improvements are obtained when the system response amplitudes in a bounded speed range is reduced by applying the adjustable lubrication. Results are in
agreement with the established fact that a significant improvement of the rotor-bearing system dynamic performance can only be obtained by applying the feedback-controlled lubrication or appropriately choosing the bearing design parameters.