Compliant foil bearing technology is at the center of NASA’s Oil-Free Turbomachinery program, which aims to replace the oil-lubricated rolling-element bearings in high-speed rotating machines with maintenance-free foil gas bearings, substantially reducing weight and cost while increasing reliability and efficiency. Because of these advantages, oil-free rotor supports are demanded for long-duration space power applications and are highly desirable for ground- and air-based rotating machinery. To support further development of this technology, the NASA Glenn Research Center added two new foil bearing test facilities that target specific gaps in previously available test capabilities.
High Pressure Journal Bearing Test Rig.
The High Pressure Journal Bearing Rig (see the preceding photograph) consists of a high-speed electrical motor with an overhung journal operating within a pressure vessel. In this configuration, foil bearing performance from 0 to 42,000 rpm can be measured at pressures from moderate vacuum up to 4.8 MPa (700 psi) at room temperature. Foil bearing power loss, typically much lower than in rolling-element bearings, can be mapped over this wide pressure and speed range, simulating a broad range of operating conditions for potential oil-free turbomachines. This test rig also supports variable-pressure testing in inert gases such as carbon dioxide, helium, and xenon, which are candidate working gases for several power cycle turbomachines, including a Brayton-cycle turboalternator for high-electrical-power space missions.
Testing of foil thrust bearings (see the following photograph) will be augmented with a new test rig that can subject oil-free thrust bearings to tens of thousands of start-stop cycles, verifying endurance of the solid lubricant coatings that have been developed at Glenn and by industry. The rig also will provide very stable operation at speeds up to 21,000 rpm and temperatures from room temperature to over 540 °C (1000 °F) to measure bearing performance at the lower speed range of their operational envelope. Solid-lubricant coating systems will be further matured by this new facility, adding a valuable experience base for designers of next-generation turbomachines. Although foil thrust bearing development lags that of foil journal bearing counterparts, this added test rig will foster a more rapid advance of foil thrust bearing technology.
Core of Low Speed Thrust Bearing Test Rig.
Thrust bearing operational performance and durability, as well as journal bearing performance at high pressure, can now be determined experimentally. The addition of these new test capabilities further diversifies NASA’s portfolio of Oil-Free Turbomachinery research assets, supporting numerous applications for ground, air, and space power and propulsion.
Find out more about the research of Glenn’s Oil-Free Turbomachinery program:
http://www.grc.nasa.gov/WWW/Oilfree/
Last updated: December 15, 2007
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