Advancements in the Performance of Aerodynamic Foil Journal Bearings: High Speed and Load Capability

An advanced-design, aerodynamic, air-lubricated foil journal bearing achieved a landmark speed of 2200 cps (132,000 rpm) and a major breakthrough in load performance of 673.5 kPa (97.7 psi). At 20°C (68°F) room temperature, normal ambient pressure, 995 cps (59,700 rpm) rotor speed, and with bearing projected pad area of 1081 mm² (1.675 in²), the bearing demonstrated a load capacity of 727.8 N (163.6 lb). The bearing also exhibited low heat generation, with about 40°C (104°F) average side leakage temperature rise. For this demonstration, a highspeed spindle utilizing a pair of 35-mm (1.375-in.) bearings and supporting a test rotor with a mass of 1.545 kg (weighing 3.41 lb) and overall length of 211 mm (8.3 in.) was successfully taken to the limiting speed of the test apparatus. This speed was set by the maximum sound velocity (Mach 1) in the spindle’s turbine wheel. The rotor/bearing speed of 4.62 × 10⁶ DN is beyond the capability of any advanced oil-lubricated ball bearings or conventional gas-lubricated bearings. The net result is a highly stable bearing at high operating speed. This paper presents the development of this air-lubricated foil journal bearing, the operational procedures used during testing, test results (dynamic analyses), and load performance characteristics.