Description:
OBJECTIVE: Improve small gas turbine engine system weight and performance by developing foil-air bearings to support the main rotor shaft (s). DESCRIPTION: Small gas turbine engines for unmanned aerial systems and man-portable electric power generators need to be as light and efficient as possible to meet mission requirements. These small gas turbine engines currently use oil lubricated, conventional ball bearings that operate at very high rotational speeds. The frictional loss of these high speed bearings represents a 5-10% loss in power. Also, the weight of the required lubrication and bearing cooling system approaches 30% of the engine system weight. Advanced foil bearings for small gas turbine engines have the potential to eliminate a large portion of these performance and weight penalties. The use of air foil bearings for small gas turbine engines has been hampered by several significant technical challenges. These challenges include bearing surface velocities above current industrial applications, the need for small compact bearing sizes with thin material sections (foils) and small well controlled clearances. Also, these small bearings need to provide high levels of radial and axial stiffness to maintain tight/well controlled compressor and turbine clearances for good engine performance. In addition, the air-foil bearings need to provide adequate damping to control rotor motion as critical speeds are encountered and balance deteriorates during field usage. Lastly, high temperature rub materials need to be validated for these thin foils that must operate through a large number of start/stop cycles in military applications. This effort seeks to develop air foil bearings for gas turbine engines with a maximum output power of up to 200 hp. PHASE I: Investigate compact foil-air bearing concepts and select candidate rub materials for high-speed, small gas turbine engine applications through modeling, empirical evaluation, pragmatic analysis and laboratory tests. Complete foil-air bearing preliminary design for the most attractive concept(s). Substantiate the weight savings of the foil-air bearing configuration in comparison to a conventional rolling-element bearing and sump layout (as a percentage of total engine weight, for target engine size). Also, the foil-air bearing shall be designed to a minimum of 1000 hours life. PHASE II: Design and fabricate an air bearing test rig, air bearing concept and small gas turbine engine modifications as necessary to accommodate foil-air bearings. Complete rig and small gas turbine engine tests to validate the foil-air bearings. Develop a dual use commercialization plan. Design to weight and life metrics as described in Phase I. PHASE III: Work with the Government and industry to construct a prototype small gas turbine engine system with advanced foil-air bearings. Conduct extended durability testing over typical military and civil use cycles. Pursue global commercial markets for this new small gas turbine engine technology. REFERENCES: 1. L."Foil Air/Gas Bearing Technology: An Overview."American Society of Mechanical Engineers 97-GT-347 (1997): n. Web. 12 Oct. 2011. 2. C. and, Mark J."Load Capacity Estimation of Foil Air Journal Bearings for Oil-Free Applications."NASA/TM 209782 (2000). 3. H."Advancements in the Performance of Aerodynamic Foil Journal Bearings High Speed and Load Capacity."STLE Transactions Vol. 41, 3 (1998): 335-340. 4. P., Locke, D.H. and, H."New-Generation Development Rigs for Testing High- Speed Air-Lubricated Thrust Bearings,"STLE Transaction, Vol. 46, 4 (2003): 556-559.
