A Comparative Study of the Dynamic Stability of a Rotor Supported by an Air-Bearing and an Air-ring Bearing

An exploration to justify the need for an air-ring around an air-bearing is done by comparing the dynamic stability plots of a rotor supported by air-bearings with and without an air-ring. Air-bearing with air-ring or air-ring bearing has pocketed feed-holes. The air-bearing without air-ring has plain feed-holes and it is referred to as air-bearing with a direct feeding system. A linearized free-vibration model rotor-bearing is used to analyze the dynamic stability. The dynamic coefficients of air-bearing with a direct feeding system and air-ring bearing are affected by whirl frequency due to the fluid compressibility effects. The stability threshold speed of the rotor air-ring bearing system is increased well above the threshold speed of the rotor air-bearing with a direct feeding system. The rotor critical mass of the rotor air-ring bearing system is smaller than that of the rotor air-bearing with a direct feeding system. The air-ring of air-ring bearing can prevent self-excited vibration in lightly loaded rotor-bearing systems.