가스 포일 베어링으로 지지된 고속 회전체의 경사각과 베어링의 기계적 예압이 고유 진동수와 불안정성 발생 속도에 미치는 영향

Abstract

School of Mechanical Systems Engineering, Kookmin University(Received 2014 March 20, 2014 ; Revised 2014 May 1, 2014 ; Accepted 2014 May 4, 2014) Abstract − This study investigates the effects of the slopes of the rotational axis and bearing preloads on the nat-ural frequencies and onset speeds of the instability of a rotor supported on gas foil bearings (GFBs). The pre-dictive model for the rotating system consists of a rigid rotor supported on two gas foil journal bearings (GFJBs)and a pair of gas foil thrust bearings (GFTBs). Each GFJB supports approximately half the rotor weight. As theslope of the rotational axis increases from 0° (horizontal rotor operation) to 90° (vertical rotor operation), theapplied load on the GFJB owing to the rotor weight decreases. The predictions show that the natural frequencyand onset speed of instability decrease significantly with an increase in the slope of the rotational axis. In a para-metric study, the nominal radial clearance and preload for the GFJB were changed. In general, a decrease in thenominal radial clearance lead to an increase in the natural frequency and onset speed of instability. For constantassembly clearance, the decrease in the preload changed the natural frequency and onset speed of instability withinsignificant improvements in the rotordynamic stability. The present predictions can be used as design guide-lines for GFBs for oil-free high-speed rotating machinery with improved rotordynamic performance.Keywords −gas foil journal bearing (가스 포일 저널 베어링), preload (예압 ), natural frequency (고유 진동수), instability(불안정성), slope of rotational axis (회전축 경사각)