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Morton-Newkirk Effect in Overhung Rotor Supported in Rolling Element Bearings

[+] Author Affiliations
Thom M. Eldridge

Shell Global Solutions, Houston, TX

Andrew Olsen

Dresser-Rand, Worcester, MA

Michael Carney

Ingersoll-Rand Energy Systems, Portsmouth, NH

Paper No. GT2009-60243, pp. 1033-1041; 9 pages
doi:10.1115/GT2009-60243
From:
  • ASME Turbo Expo 2009: Power for Land, Sea, and Air
  • Volume 6: Structures and Dynamics, Parts A and B
  • Orlando, Florida, USA, June 8–12, 2009
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4887-6 | eISBN: 978-0-7918-3849-5
  • Copyright © 2009 by ASME

abstract

Morton Effect is a known rotordynamic phenomenon associated with fluid film bearings, where viscous heating creates a uni-directional temperature rise in the bearing journal, leading to thermal growth and subsequent bow of the rotor. This results in an unbalance distribution that exacerbates the original unbalance, increasing the heating and bow, resulting in an unstable, or self-amplifying, response. Heretofore, this phenomenon has only been reported in fluid film bearings, as it is traditionally associated with the viscous heating from shearing of the oil. There is also similar behavior associated with phenomenon named the Newkirk Effect where the same mechanics of heating, thermal growth and bowing of a shaft occurs, but the source of heating is a labyrinth rub. This paper describes an incident where such a series of interactions was experienced with a rolling-element bearing (REB). Instead of being driven by viscous shearing of the oil through the minimum film clearance, the uni-directional heating of the rotor results from unbalance and the sliding or dynamic friction of the balls on the inner race or rub of a near-by seal. Rotordynamic analysis was used to derive a correlation between measured vibration levels and temperature rise resulting in predictable bowing of the shaft in a 45,000 RPM fixed speed 250 kW microturbine having an overhung rotor supported by two rolling element bearings. Vibration response was measured with proximity probes along the rotor and temperature predictions were verified against physical evidence in the bearing races. The information gained in this effort was used to establish assembly tolerance and vibration acceptance criteria for factory testing of the turbine. This behavior has internally been described as “REB Morton Effect.” The paper describes the vibration investigation; bearing evaluation; rotordynamic modeling, analysis and verification; design and assembly corrections, and subsequent testing.

Copyright © 2009 by ASME

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