Unbalance Response of the Rotors Supported on Gas Foil Bearing Integrated with Active Magnetic Bearing.

Background: Gas Foil Bearings (GFBs) have fulfilled most of the requirements of novel oil-free turbomachinery. It has been considered as an alternative to traditional bearings in turbopumps, turbocompressors and turbochargers. However, they are prone to instabilities due to its low damping characteristics. Therefore, a hybrid bearing combining the GFBs and Active Magnetic Bearings (AMBs) has been in rigorous study due to its obvious advantages. Purpose: The main aim of this paper is to provide a coupled time domain numerical model of the rotor supported on hybrid GFBs. The developed non-dimensional model has been used to investigate the capability of hybrid GFBs to mitigate the effect of unbalance force and in turn instability. Further, the ability of the hybrid GFB to withstand unbalance at an arbitrary time has also been investigated. Methods: The magnetic force generated is calculated using reluctance network method while fluid film forces are obtained by solving the governing Reynolds equation. The magnetic force of the AMB is non-dimensionalized in line with the fluid film forces of the conventional GFB. The non-dimensionalized fluid film forces from the GFBs and the electromagnetic forces from the EMAs are integrated into the equations of motion of the rotor. The response is then recorded for different operating parameters of the rotor. Results: The sub-synchronous frequency which is the dominating frequency in case of the conventional GFB is eliminated due to the implementation of hybrid GFB. It has been demonstrated that the hybrid GFB has higher capability to withstand unbalance compared to conventional GFB. It has been observed that higher control current is required for higher unbalance eccentricity. Moreover, the hybrid GFB is also capable of adapting to the unbalance occurring at an arbitrary time. [ABSTRACT FROM AUTHOR]