Rotordynamic Performance of an Oil-Free Turbo Blower Focusing on Load Capacity of Gas Foil Thrust Bearings

Rotordynamic Performance of an Oil-Free Turbo Blower Focusing on Load Capacity of Gas Foil Thrust Bearings
Rotordynamics; Oil-Free; Turbo Blower; Load Capacity; Gas Foil Bearing; Gas Foil Thrust Bearing
Issue Date
Journal of engineering for gas turbines and power
VOL 134, NO 2, 022501-1-022501-7
Engineered design of modern efficient turbomachinery based on accurate model predictions is of importance as operating speed and rate power increase. Industrial applications use hydrodynamic fluid film bearings as rotor support elements due to their advantages over rolling element bearings in operating speed, system stability (rotordynamic and thermal), and maintenance life. Recently, microturbomachinery (<250 kW) implement gas foil bearings (GFBs) as its rotor supports due to its compact design without lubricant supply systems and enhanced stability characteristics. To meet the needs from manufacturers, the turbomachinery development procedure includes a rotordynamic design and a gas foil journal bearing (GFJB) analysis in general. The present research focuses on the role of gas foil thrust bearings (GFJBs) supporting axial load (static and dynamic) in an oil-free turbo blower with a 75 kW (100 HP) rate power at 30,000 rpm. The turbo blower provides a compressed air with a pressure ratio of 1.6 at a mass flow rate of 0.92 kg/s, using a centrifugal impeller installed at the rotor end. Two GFJBs with a diameter of 66mm and a length of 50 mm and one pair of GFTB with an outer diameter of 144 mm and an inner diameter of 74 mm support the rotor with an axial length of 493 mm and a weight of 12.7 kg. A finite element rotordynamic model prediction using predicted linearized GFJB force coefficients designs the rotor-GFB system with stability at the rotor speed of 30,000 rpm. Model predictions of the GFTB show axial load carrying performance. Experimental tests on the designed turbo blower; however, demonstrate unexpected large amplitudes of subsynchronous rotor lateral motions. Post-inspection reveals minor rubbing signs on the GFJB top foils and significant wear on the GFTB top foil. Therefore, GFTB is redesigned to have the larger outer diameter of 166 mm for the enhanced load capacity, i.e., 145%, i
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