An experimental study on the applicability of acoustic emission to detection of lift-off state in gas foil bearings

Abstract Gas foil bearings (GFBs) are fluid dynamic bearings with applications in high-speed lightweight machinery. One of the important parameters in GFBs is the lift-off speed. It indicates a speed above which there is no occurrence of dry friction and wear between the rotor and bearing, the so-called lift-off state. There are various techniques for determination of the lift-off state. However, they come with major limitations and complexities for use in real-world applications, especially in high-speed machinery. In recent years, monitoring the lift-off condition in journal bearings based on acoustic emissions (AE) has been investigated and shown to be suitable for this type of bearing. Nevertheless, its applicability to GFBs is yet not known, as there has been no practical investigation on AE signals in GFBs. In the present work, the applicability of AE measurements to detection of lift-off state in GFBs is explored experimentally based on previous studies on journal bearings. The results demonstrate that AE measurements are a potential alternative to conventional methods in determining the lift-off state in GFBs. The comparison between features of AE signals, measured at two different locations on the bearing, with the friction torque as the reference exhibits the applicability of AE measurements to detection of lift-off state.