The paper presents an analytical and experimental investigation aimed at eliciting the thermal characteristics of air lubricated compliant foil bearings. A Couette Approximation to the energy equation is used in conjunction with the compressible Reynolds equation to obtain a theoretical temperature distribution in the air used as a lubricant. The effect of temperature on the thermal properties of the working fluid is included. In parallel, an experimental program was run on a 100 mm diameter foil bearing operating at speeds up to 30,000 rpm employing cooling air across the bearing. The temperature rise of the cooling air provided an indication of the amount of heat energy conducted across the top foil of the bearing from the hydrodynamic film. The temperatures resulted from some tests are compared with the temperatures predicted by the analysis, and maximum over-prediction of about 19 percent was obtained. This simplified approach provides us with reasonably predicted temperatures. By comparing the theoretical heat dissipation obtained from the analytical predicted temperatures with the amount of heat carried away by the cooling air it was possible to arrive at the relative quantities of heat transferred from the bearing by convection via side leakage and by conduction via the top foil. From these comparisons it was deduced that about an average of 80 percent of the heat energy is carried away by conduction. The transient temperatures of the foil bearing in conducted tests for various speeds and loads are also presented.
Foil bearings are a key enabling technology for advanced and oil-free rotating machinery. In certain applications, they provide a level of performance that is difficult or impossible to match with other technologies. A number of reasonably successful analytical techniques to predict bearing load capacity, power loss, and stiffness have been developed. Prediction of damping, however, has remained problematic. This work presents a fresh look at the damping problem. Using a simplified representation of a bump foil, this work considers explicitly adding the load dependence of the friction force. This approach is shown to provide a good match to previous experimental data. Parametric study results for the various model parameters are presented to examine the characteristics of this model. It is concluded that the load-dependent frictional force is important to consider for a bump foil damping model.
An extensive survey of the experimental research on the static and/or dynamic characteristics of fixed geometry, hydrodynamic journal bearings, available in English, in the open literature is presented. The type(s) of bearing, size of bearing(s) and range of parameters measured in each work are reported for slightly over 100 published experimental works. In addition, some general observations about the available experimental data sets are made. This annotated survey is intended to help the analytical community by providing an extensive list of sources of experimental data for use in analysis verification. It is intended to help the experimental community by highlighting the shortcomings of the available literature, as well as by providing a list of sources for appropriate data to help with current and future test rig debugging.
To meet the advanced bearing needs of modern turbomachinery, a hybrid foil-magnetic hybrid bearing system was designed, fabricated, and tested in a test rig designed to simulate the rotor dynamics of a small gas turbine engine (31 kN to 53 kN thrust class). This oil-free bearing system combines the excellent low and zero-speed capabilities of the magnetic bearing with the high-load capacity and high-speed performance of the compliant foil bearing. An experimental program is described which documents the capabilities of the bearing system for sharing load during operation at up to 30,000 rpm and the foil bearing component’s ability to function as a backup in case of magnetic bearing failure. At an operating speed of 22,000 rpm, loads exceeding 5300 N were carried by the system. This load sharing could be manipulated by an especially designed electronic control algorithm. In all tests, rotor excursions were small and stable. During deliberately staged magnetic bearing malfunctions, the foil bearing proved capable of supporting the rotor during continued operation at full load and speed, as well as allowing a safe rotor coastdown. The hybrid system tripled the load capacity of the magnetic bearing alone and can offer a significant reduction in total bearing weight compared to a comparable magnetic bearing.
To meet the advanced bearing needs of modern turbomachinery, a hybrid foil-magnetic hybrid bearing system was designed, fabricated and tested in a test rig designed to simulate the rotor dynamics of a small gas turbine engine (31 kN to 53 kN thrust class). This oil-free bearing system combines the excellent low and zero-speed capabilities of the magnetic bearing with the high load capacity and high speed performance of the compliant foil bearing. An experimental program is described which documents the capabilities of the bearing system for sharing load during operation at up to 30,000 RPM and the foil bearing component’s ability to function as a back-up in case of magnetic bearing failure. At an operating speed of 22,000 RPM, loads exceeding 5300 N were carried by the system. This load sharing could be manipulated by an especially designed electronic control algorithm. In all tests, rotor excursions were small and stable. During deliberately staged magnetic bearing malfunctions, the foil bearing proved capable of supporting the rotor during continued operation at full load and speed, as well as allowing a safe rotor coast-down. The hybrid system tripled the load capacity of the magnetic bearing alone and can offer a significant reduction in total bearing weight compared to a comparable magnetic bearing.
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