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.

The servo valve input signal and the radial injection pressure are the two main parameters responsible for dynamically modifying the journal oil film pressure and generating active fluid film forces in controllable fluid film bearings. Such fluid film forces, resulting from a strong coupling between hydrodynamic, hydrostatic and controllable lubrication regimes, can be used either to control or to excite rotor lateral vibrations. An accurate characterization of the active oil film forces is of fundamental importance to elucidate the feasibility of applying the active lubrication as non-invasive perturbation forces, or in other words, as a “calibrated shaker”, to perform in-situ rotordynamic tests. The main original contributions of this paper are three: a) the experimental characterization of the active fluid film forces generated in an actively-lubricated tilting-pad journal bearing in the frequency domain and the application of such a controllable bearing as a calibrated shaker aiming at determining the frequency response function (FRF) of rotordynamic systems; b) experimental quantification of the influence of the supply pressure and servo valve input signal on the FRF of rotor-journal bearing systems; c) experimental indication of how small such active fluid film forces (perturbation forces) should be, in order to perturb the rotor-journal bearing system without significantly changing its dynamic characteristics. To validate the experimental procedure and results obtained via actively-lubricated bearing, similar experimental tests are carried out using an electro-magnetic shaker. Very good agreements between the two experimental approaches are found. Maximum values of the main input parameters, namely servo valve voltage and radial injection pressure, are experimentally identified/suggested with the objective of obtaining non-invasive perturbation forces.

No abstract

No abstract

Tilting-Pad Journal Bearings (TPJB) are commonly used on high-performance turbomachinery due to their excellent stability properties at high speed when compared to other designs for oil film bearings. Hence, efforts have been made to improve the accuracy for the available models for these mechanical devices, achieving nowadays an elasto-thermo-hydrodynamic formulation. On the other hand, the basic design of the Tilting-Pad Journal Bearing has been modified in order to transform it into a smart machine element. One approach to do so is to inject pressurized oil directly into the bearing clearance through holes drilled across the bearing pads. By adjusting the injection pressure, it is possible to modify the dynamic characteristics of the bearing. A controllable lubrication regime is obtained, allowing to expand the operational boundaries of the original design. This work focuses on presenting an elasto-thermo-hydrodynamic model (ETHD) for the Tilting-Pad Journal Bearing, including the effect of the controllable lubrication system. The basic model is validated by comparing its results against theoretical and experimental results available in the literature. Then, the validated code is used to show the benefits of applying a controllable lubrication regime, by means of the modification of the thermal and dynamic behaviour of the bearing.