Rotordynamics Performance of Hybrid Foil Bearing Under Forced Vibration Input

Abstract

Foil bearings (FB) are one type of hydrodynamic air/gas bearings but with a compliant bearing surface supported by structural material that provides stiffness and damping to the bearing. The hybrid foil bearing (HFB) in this paper is a combination of a traditional hydrodynamic foil bearing with externally pressurized air/gas supply system to enhance load capacity during the start and to improve thermal stability of the bearing. The HFB is more suitable for relatively large and heavy rotors where rotor weight is comparable to the load capacity of the bearing at full speed and extra air/gas supply system is not a major added cost. With 4448–22,240 N thrust class turbine aircraft engines in mind, the test rotor is supported by HFB in one end and duplex rolling element bearings (REB) in the other end. This paper presents experimental work on HFB with diameter of 102 mm performed at the U.S. Air force Research Laboratory (AFRL). Experimental works include: measurement of impulse response of the bearing to the external load corresponding to rotor's lateral acceleration of 5.55 g, forced response to external subsynchronous excitation, and high-speed imbalance response. A nonlinear rotordynamic simulation model was also applied to predict the impulse response and forced subsynchronous response. The simulation results agree well with the experimental results. Based on the experimental results and subsequent simulations, an improved HFB design is also suggested for higher impulse load capability up to 10 g and rotordynamics stability up to 30,000 rpm under subsynchronous excitation.

The Two-Pad: A Novel Gas Foil Bearing for Fuel Cell Vehicles

“…(i) Studies on subsynchronous vibration due to nonconservative gas film forces [31][32][33][34][35] (ii) Studies on synchronous and supersynchronous vibration due to rotor rotation [36][37][38][39] (iii) Studies on the system response to harmonic vibration and shock [40][41][42][43][44] Although most vibration studies have focused on these three categories, in the real world, systems are often subjected to random vibrations from the environment, especially in in-vehicle devices, where the forces acting on vehicles traveling over irregular terrain are usually modeled as random vibrations [45]. Random vibrations are vibrations that cannot be described by a deterministic function, such as bumps in a vehicle's path and vibrations in an aircraft fuselage due to atmospheric turbulence [46], and random vibrations have been shown to have destructive effects on many devices [45,47].…”

Numerical Investigation of Unsteady Characteristics of Gas Foil Journal Bearings with Fluid–Structure Interaction

“…The dynamic response along the horizontal and vertical directions was analyzed using the system state trajectory, Poincare diagram, power spectrum, and bifurcation plot. Kim et al [36] obtained the impact response of GFJB from an external 5.55 g load of lateral acceleration. It was found that there was synchronous vibration and sub-synchronous vibration in the rotor supported by the foils.…”