Gas bearings in oil-free microturbomachinery for gas process applications and power generation (<400 kW) must be reliable and inexpensive, ensuring low drag power and thermal stability. Bump-type foil bearings (BFBs) and overleaf-type foil bearings are in use in specialized applications, though their development time (design and prototyping), exotic materials, and excessive manufacturing cost still prevent their widespread usage. Metal mesh foil bearings (MMFBs), on the other hand, are an inexpensive alternative that use common materials and no restrictions on intellectual property. Laboratory testing shows that prototype MMFBs perform similarly as typical BFBs, but offer significantly larger damping to dissipate mechanical energy due to rotor vibrations. This paper details a one-to-one comparison of the static and dynamic forced performance characteristics of a MMFB against a BFB of similar size and showcases the advantages and disadvantages of MMFBs. The bearings for comparison are a generation I BFB and a MMFB, both with a slenderness ratio L/D = 1.04. Measurements of rotor lift-off speed and drag friction at start-up and airborne conditions were conducted for rotor speeds to 70 krpm and under identical specific loads (W/LD = 0.06 to 0.26 bar). Static load versus bearing elastic deflection tests evidence a typical hardening nonlinearity with mechanical hysteresis, the MMFB showing two to three times more material damping than the BFB. The MMFB exhibits larger drag torques during rotor start-up, and shut-down tests though bearing lift-off happens at lower rotor speeds (∼15 krpm). As the rotor becomes airborne, both bearings offer very low drag friction coefficients, ∼0.03 for the MMFB and ∼0.04 for the BFB in the speed range 20–40 krpm. With the bearings floating on a journal spinning at 50 krpm, the MMFB dynamic direct force coefficients show little frequency dependency, while the BFB stiffness and damping increases with frequency (200–400 Hz). The BFB has a much larger stiffness and viscous damping coefficients than the MMFB. However, the MMFB material loss factor is at least twice as large as that in the BFB. The experiments show that the MMFB, when compared to the BFB, has a lower drag power and earlier lift-off speed and with dynamic force coefficients having a lesser dependency on whirl frequency excitation.
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e-mail: Lsanandres@tamu.edu
e-mail: thomas.chirathadam@swri.org
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October 2012
Gas Turbines: Structures And Dynamics
A Metal Mesh Foil Bearing and a Bump-Type Foil Bearing: Comparison of Performance for Two Similar Size Gas Bearings
Luis San Andrés,
Luis San Andrés
Fellow ASME
Mechanical Engineering Department,
e-mail: Lsanandres@tamu.edu
Texas A&M University
, College Station, TX 77843-3123
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Thomas Abraham Chirathadam
Thomas Abraham Chirathadam
Research Engineer
Mechanical Engineering Division,
e-mail: thomas.chirathadam@swri.org
Southwest Research Institute®
, San Antonio, TX 78228-0510
Search for other works by this author on:
Luis San Andrés
Fellow ASME
Mechanical Engineering Department,
Texas A&M University
, College Station, TX 77843-3123e-mail: Lsanandres@tamu.edu
Thomas Abraham Chirathadam
Research Engineer
Mechanical Engineering Division,
Southwest Research Institute®
, San Antonio, TX 78228-0510e-mail: thomas.chirathadam@swri.org
J. Eng. Gas Turbines Power. Oct 2012, 134(10): 102501 (13 pages)
Published Online: August 14, 2012
Article history
Received:
June 20, 2012
Revised:
June 21, 2012
Published:
August 14, 2012
Citation
San Andrés, L., and Abraham Chirathadam, T. (August 14, 2012). "A Metal Mesh Foil Bearing and a Bump-Type Foil Bearing: Comparison of Performance for Two Similar Size Gas Bearings." ASME. J. Eng. Gas Turbines Power. October 2012; 134(10): 102501. https://doi.org/10.1115/1.4007061
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