ROTORDYNAMIC PERFORMANCE MEASUREMENT OF AN OIL-FREE TURBOCOMPRESSOR SUPPORTED ON GAS FOIL BEARINGS

Abstract

This paper presents the results of speed-up and coastdown tests with a variation in the radial clearance of gas foil bearings. The test facility includes a high speed driving motor and a two-stage turbocompressor whose shafts are coupled using a flexible coupling. The rate power of the permanent magnet synchronous (PMS) motor is 300 HP (225kW) at the maximum rotating speed of 60krpm. The turbocompressor shaft has two impellers at its side ends and compresses air while it rotates at the same speed as the motor. Four gas foil bearings (GFBs) support the coupled multi-shafts at the motor and compressor sides. To determine the rotordynamic performance of the coupled motor - compressor system, a series of experiments are conducted for increasing radial clearances of the motor side test GFBs from 150 mu m to 300 mu m with a 50 mu m increment, while the radial clearance of the compressor side GFBs are fixed at 150 mu m. The test results show that increasing radial clearance delays the onset speed of rotor subsynchronous whirl motions and decreases the whirl frequency. As the radial clearance decreases, the rotor peak amplitude at the critical speed similar to 15 krpm decreases significantly.