1 Department of Mechanical Engineering, Technical University of Denmark2 Solid Mechanics, Department of Mechanical Engineering, Technical University of Denmark
The current trends regarding turbomachinery design and operation demand for an expansion of the operational boundaries of these mechanical systems, regarding production rate, reliability and adaptability. In order to face the new requirements, it is necessary to migrate towards a new concept, where the machine is defined as a mechatronic system. This integrated approach comprises the usage of machine elements capable of modifying their characteristics, by using in a combined way mechanical elements, sensors, processing units and actuators. The research project entitled "Mechatronics Applied to Fluid Film Bearings: Towards more Efficient Machinery" was aimed at improving the state of the art regarding the usage of fluid film bearings as "smart" machine elements. Specifically, this project dealt with a tilting pad journal bearing design that features a controllable lubrication system, capable of modifying the static, thermal and dynamic properties of the bearing, depending on the operational requirements at hand. The research activities carried out during the project included both theoretical as well as experimental investigations, using a test rig consisting of a rigid rotor supported by a tilting pad bearing featuring the controllable lubrication technology. These investigations were aimed at three main objectives: firstly, the improvement of the existing theoretical model for the tilting pad journal bearing with controllable lubrication; secondly, the experimental validation of the available theoretical model, regarding its capability of predicting the static, thermal and dynamic behavior of the controllable bearing; and lastly, the experimental evaluation of the feasibility of using the controllable bearing as a calibrated actuator. Within these areas, the main original contributions and results achieved during this research project are: the obtention of a theoretical model for the studied bearing, featuring a controllable thermoelastohydrodynamic regime; the expansion of the theoretical model for the hydraulic system associated with the controllable bearing, by including the effect of the pipelines dynamics; the experimental confirmation of the validity of the theoretical model, regarding the prediction of static and thermal characteristics of the controllable bearing; the experimental characterization of the active oil film forces generated by the bearing in the frequency domain; and the successful experimental application of this controllable machine element as a calibrated shaker, for rotordynamics parameter identification purposes. The theoretical model of the studied controllable bearing proves to be adequate to predict the static and thermal behavior of the bearing. Furthermore, it is suitable to characterize the dynamic behavior of the bearing in the low frequency range, regarding the magnitude and phase of the active fluid film forces with respect to the control signal. However, the experimental characterization of the active fluid film forces generated by the controllable bearing revealed the existence of additional dynamic effects in the system, apart from the ones related to the servovalve and pipelines. These additional dynamics become specially relevant for applications where the controllable bearing must generate active forces in the high frequency range. Specifically, a phase lag effect was observed between the pressure in the injection nozzle and the active fluid film force acting over the rotor. This effect is not included in the current theoretical model of the controllable bearing, and it could arise from dynamic effects within the oil flow in the injection nozzle and bearing clearance. Consequently, new research fronts are opened within the field of controllable fluid film bearings.