Experimental Study on Dynamic Performance of Compliant Aerodynamic Foil Journal Air Bearings

A test rig was built to study the performances of new compliant aerodynamic foil journal air bearings. This paper introduced an experimental method to identify eight linear dynamic coefficients of the foil gas bearings under different excitation frequencies. The experiment was performed when the static load and the rotating speed were 60 N and 9 000 rpm, respectively. The disturbed speed and acceleration of the journal center were obtained by the method of center difference of its displacement. In time domain, the linear stiffness and damping coefficients of each excitation frequency were calculated by means of least mean square. Finally, the effect of the excitation frequency on the dynamic characteristics of the bearing was investigated. Experimental results show that the vibration orbit of the journal center is elliptic. And with the excitation frequency increasing, the perturbation amplitudes of the journal center increase, but the direct terms of the stiffness and damping coefficients of the bearing decrease. The cross-coupling terms change little with the changes of dynamic excitation frequency, and their values are much smaller than those of the direct terms. When the excitation frequency is equal to the working frequency of the rotor, because of the effect of the components of the working frequency, the perturbation amplitude of the journal center increase significantly and the direct terms of the stiffness and damping coefficients are much smaller than those of other excitation frequencies.