Experimental identification of dynamic coefficients of lightly loaded tilting-pad bearings under several lubrication regimes

This paper presents the identified dynamic coefficients of a lightly loaded actively lubricated bearing under three lubrication regimes: passive, hybrid and feedback-controlled. The goal is to experimentally demonstrate the feasibility of modifying the bearing dynamic properties via active lubrication. Dominated by the latest two regimes, the bearing properties become adjustable or controllable due to the injection of either a constant or variable pressurized oil flow. Such a flow is regulated by a hydraulic control system composed of (a) a high-pressure oil supply unit, (b) servovalves, (c) radial injection nozzles, (d) displacement sensors and (e) well-tuned digital controllers. A scaled-down industrial rotor featuring active lubrication, composed of a flexible rotor supported by a four-rocker load-between-pads tilting-pad bearing under light load condition, is used for this objective. The experimental identification is performed by means of measured frequency response functions and a rotor finite element model. Predicted coefficients are also provided for benchmarking. Comparing results between the different regimes, presented along with their expanded uncertainty, provides the experimental evidence of the bearing properties modification via active lubrication.</jats:p

WTC2005-63663 ACTIVE LUBRICATION FOR ELIMINATING INSTABILITY PROBLEMS IN ROTATING MACHINES

ABSTRACT When the hydrostatic and the hydrodynamic lubrication are simultaneously combined in a journal bearing, with the aim of reducing wear between rotating and stationary parts, one refers to the hybrid lubrication, which offers the advantages of both lubrication mechanisms. When part of the hydrostatic pressure is also dynamically modified by means of hydraulic control systems, one refers to the active lubrication. By the combination of fluid power, electronics and control theory, the active lubrication makes feasible the reduction of wear and the attenuation of rotor instabilities. Significant reduction of resonance peaks is demonstrated in a test rig, specially designed with the aim of experimentally exploring the potential of the active lubrication. Experiments are led in the frequency domain. INTRODUCTION High efficiency rotating machines, working at severe pressure and flow conditions, demand continuous monitoring and control of vibration levels. One of the ways of reducing vibration amplitudes in rotating machines is the use of hydrodynamic bearings. Among the hydrodynamic bearings, the tilting-pad bearings are those which show the best stability properties. Nevertheless, in many cases, due to aerodynamic excitations (crosscoupling effect) instabilities can occur, if the amount of bearing damping (at full load condition, i.e. high maximum continuous speed) is not enough to ensure a reasonable stability margin. One of the ways of improving this stability margin is by applying ac

On the Incorporation of Friction Into a Simultaneously Coupled Time Domain Model of a Rigid Rotor Supported by Air Foil Bearings

Despite decades of research, the dynamics of air foil bearings (AFBs) are not yet fully captured by any model, suggesting that the fundamental mechanisms of the AFB and their relative merits are not yet fully understood. The recent years have seen promising results from nonlinear time domain models, allowing the dynamic pressure– compliance interaction and the unsteady terms of the compressible Reynolds equation to be considered. By including the simple elastic foundation model (SEFM) in a fully coupled simultaneous time integration, the dynamics of a rotor supported by industrial AFBs have previously been modelled by the authors, leading to good agreement with experimental results. In this paper, the authors investigate the substitution of the SEFM for a new foil structure model which is based on directly measurable quantities and includes frictional energy dissipation in the foil structure. An important finding is that the incorporation of a friction model into the global model cannot be reconciled with a simultaneous time solution without the inclusion of the foil inertia. The resulting AFB model allows the effects of friction on AFB performance to be directly examined and leads to the questioning of friction’s role and its significance to the operation of AFBs