An Experimental Investigation into the Temperature Profile of a Compliant Foil Air Bearing

Abstract

Public reporting burden for this collection of Information is estimated to average 1 liour per response, including tlie time for reviewing instructions, searcfiing existing data sources, gatfiering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503. AGENCY USE ONLY (/.eai'e WanA)REPORT DATE May 2004 REPORT TYPE AND DATES COVERED Technical Memorandum TITLE AND SUBTITLE 12b. DISTRIBUTION CODE ABSTRACT (Maximum 200 words)A series of tests was performed to determine the internal temperature profile in a compliant bump-type foil journal air bearing operating at room temperature under various speeds and load conditions. The temperature profile was collected by instrumenting a foil bearing with nine, type K thermocouples arranged in the center and along the bearing's edges in order to measure local temperatures and estimate thermal gradients in the axial and circumferential directions. To facilitate the measurement of maximum temperatures from viscous shearing in the air film, the thermocouples were tack welded to the backside of the bumps that were in direct contact with the top foil. The mating journal was coated with a high temperature solid lubricant that, together with the bearing, underwent high temperature start-stop cycles to produce a smooth, steady-state run-in surface. Tests were conducted at speeds from 20 to 50 krpm and loads ranging from 9 to 222 N. The results indicate that, over the conditions tested, both journal rotational speed and radial load are responsible for heat generation with speed playing a more significant role in the magnitude of the temperatures. The temperatiire distribution was nearly symmetric about the bearing center at 20 and 30 krpm but became slightiy skewed toward one side at 40 and 50 krpm. Surprisingly, the maximum temperatores did not occur at the bearing edge where the minimum film thickness is expected but rather in the middle of the bearing where analytical investigations have predicted the air film to be much thicker. Thermal gradients were common during testing and were strongest in the axial direction from the middle of the bearing to its edges, reaching 3.78 °C/mm. The temperature profile indicated the circumferential thermal gradients were negligible. SUBJECT TERMSFoil air bearings; Gas bearings; Turbomachinery • TECHNICAL PUBLICATION. Reports of completed research or a major significant phase of research that present the results of NASA programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NA...

Thermal Management Techniques for Oil-Free Turbomachinery Systems

“…The startstop cycles act as a polishing wear mechanism between the asperities of the top foil and coating, resulting in a smooth, glossy, oxide-rich surface on the coating and the development of a solid lubricant layer on the foil surface (ref. 14). After the break-in cycles the final coating surface roughness was approximately 0.2 μm.…”

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“…It was found that the temperature rise slope during the rotor speed coast down was bigger than the slope during the rotor speed up. Radil, et al, (2004) performed a series of tests to determine the internal temperature profile in a bump foil air bearing operating at room temperature under various load and speed conditions. Tests were conducted at loads from 9 to 222 N and speeds ranged from 20 to 50 krpm.…”

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