Abstract
Gas foil bearings (GFBs) are machine elements used to support rotating shafts in high-speed applications, receiving increasing interest due to their oil-free feature (gas lubrication), reliability and simplicity. However, their applicability is limited due to the low load capacity as the dynamic viscosity of the gas (ambient air, or other) is lower than this of the oil (or other fluid). In the last 50 years, gas foil bearings have increased (at least doubled) their load capacity as pioneering work on the bearing design has taken place; this was mainly on tribological aspects of the foil surface and on dynamic aspects of foil properties. GFBs still face instability issues at high speeds, at least at higher speeds than the respective threshold speed of instability of an oil lubricated bearing. This paper investigates the potential to increase stability threshold of GFBs further, by active configuration of the foil shape, in order to render the optimum stability characteristics (higher damping) at discrete speeds. The analysis includes a simple rigid Jeffcott rotor model with unbalance, mounted on two active gas-foil bearings (AGFBs). The gas lubrication problem is coupled to thermal flow and structural deformation of the foil. An optimization technique is used to configure the foil according to a stability index, this being the dominant pair of eigenvalues. It is found that specific foil configurations can establish an instability-free operating range up to DN values (DN = Diameter [mm] times N [RPM]) corresponding to the speed of sound (DN \(\approx \,6.5e6\)), for both small (D30) and large (D100) AGFB applications.
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Gavalas, I., Papadopoulos, A., Chasalevris, A. (2023). Investigation of Active Configuration in Gas Foil Bearings for Stable Ultra High-Speed Operation. In: Chasalevris, A., Proppe, C. (eds) Advances in Active Bearings in Rotating Machinery. ABROM 2022. Lecture Notes in Mechanical Engineering. Springer, Cham. https://doi.org/10.1007/978-3-031-32394-2_9
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DOI: https://doi.org/10.1007/978-3-031-32394-2_9
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