The journal bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order 2 million rpm in order to enable high-power densities with turbomachinery tip speeds near 500 m/s. These journal bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas bearings. Thus, the ultra-short micro gas journal bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultrashort hydrostatic gas journal bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.
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ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference
September 2–6, 2003
Chicago, Illinois, USA
Conference Sponsors:
- Design Engineering Division and Computers and Information in Engineering Division
ISBN:
0-7918-3703-3
PROCEEDINGS PAPER
Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings
Z. S. Spakovszky,
Z. S. Spakovszky
Massachusetts Institute of Technology, Cambridge, MA
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L. X. Liu
L. X. Liu
Massachusetts Institute of Technology, Cambridge, MA
Search for other works by this author on:
Z. S. Spakovszky
Massachusetts Institute of Technology, Cambridge, MA
L. X. Liu
Massachusetts Institute of Technology, Cambridge, MA
Paper No:
DETC2003/VIB-48468, pp. 1407-1416; 10 pages
Published Online:
June 23, 2008
Citation
Spakovszky, ZS, & Liu, LX. "Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings." Proceedings of the ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. Volume 5: 19th Biennial Conference on Mechanical Vibration and Noise, Parts A, B, and C. Chicago, Illinois, USA. September 2–6, 2003. pp. 1407-1416. ASME. https://doi.org/10.1115/DETC2003/VIB-48468
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