Experiments on the Stability of Two Flexible Rotors in Tilting Pad Bearings

Proceedings of the Institution of Mechanical Engineers, Part J:

2016

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.

Section: Introductionmentioning

confidence: 83%

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

Salazar

Proceedings of the Institution of Mechanical Engineers, Part J:

2016

“…Tilting-pad journal bearings (TPJB) are commonly used in turbomachinery, due to its improved stability characteristics when compared to other fluid film bearings alternatives [1,2]. Although a versatile design, its static, thermal and dynamic properties are "fixed" at the design stage.…”

Section: Accepted Manuscript N O T C O P Y E D I T E mentioning

confidence: 99%

Tilting-Pad Journal Bearings With Active Lubrication Applied as Calibrated Shakers: Theory and Experiment

Varela

Journal of Vibration and Acoustics

2014

In recent years, a continuous research effort has transformed the conventional tilting-pad journal bearing (TPJB) into a mechatronic machine element. The addition of electromechanical elements provides the possibility of generating controllable forces over the rotor as a function of a suitable control signal. Such forces can be applied in order to perform parameter identification procedures “in situ,” which enables evaluation of the mechanical condition of the machine in a noninvasive way. The usage of a controllable bearing as a calibrated shaker requires obtaining the bearing specific frequency dependent calibration function, i.e., the transfer function between control signal and force over the rotor. This work presents a theoretical model of the calibration function for a TPJB with active lubrication. The bearing generates controllable forces by injecting pressurized oil directly into the bearing clearance. The injected flow is controlled by means of a servovalve. The theoretical model includes the dynamics of the hydraulic system using a lumped parameter approach, which is coupled with the bearing oil film using a modified form of the Reynolds equation. The oil film model is formulated considering an elastothermohydrodynamic lubrication regime. New contributions to the mathematical modeling are presented, such as the inclusion of the dynamics of the hydraulic pipelines and the obtention of the bearing calibration function by means of harmonic analysis of a linearized form of the controllable bearing constitutive equations. The mathematical model is used to study the relevance and effects of different parameters on the calibration function, aiming at providing general guidelines for the active bearing design. Finally, experimental results regarding the calibration function and the usage of the studied bearing as a calibrated shaker provide insight into the possibilities of application of this technology.

“…Works related to control design for active TPJBs can be found in [20,21,22,23,24,25,26]. In the industry, the majority of the critical machines feature flexible rotors which make them worth analysing when supported by active TPJBs, in the same way as when they are supported by conventional TPJBs [27,28,29,30,31,32]. In rotating systems, the bearing dynamic properties heavily influence the whole system dynamics because they provide the main source of energy dissipation through the lubricating fluid film.…”

Section: Introductionmentioning

confidence: 99%

Active tilting-pad journal bearings supporting flexible rotors: Part I – The hybrid lubrication

Salazar

Tribology International

2017

This is part I of a twofold paper series, of theoretical and experimental nature, presenting the design and implementation of model-based controllers meant for assisting the hybrid and developing the feedback-controlled lubrication regimes in active tilting-pad journal bearings (active TPJBs). In part I, the flexible rotoractive TPJB modelling is thoroughly covered by establishing the link between the mechanical and hydraulic systems for all regimes. The hybrid lubrication is herein covered in depth; from a control viewpoint, an integral controller to aid such a regime is designed using model-based standard tools. Results show slight improvement on the system dynamic performance by using the hybrid lubrication instead of the passive one. Further improvements are pursued with the active lubrication in part II.