Self-excited Vibration of Rotor-Casing due to Dry Friction

Recently, in order to increase the performances of rotating machinery, the radial clearance between the rotor and casing has become smaller and smaller. As a result, if the rotor contact with casing, severe self excited vibration may occur in the rotating machinery, so called “Dry-Whip”. Especially, self excited vibration with change of rotating speed (Contact type backward whirling) is able to occur under very small clearance condition. This paper presents an analytical and experimental study of such self excited vibration due to the contact which occurs between rotor and casing system under the finite driving torque. As a result, it is shown that the rotor shows two different vibration behaviors due to some physical conditions of the system (for example, the natural frequency of casing). These behaviors show the following difference. 1. vibration of different phase between rotor and casing (zero or 180 degrees). 2. amplitude of whirling which is larger than clearance or not. 3. frequency of rotor and casing whirling which is higher than natural frequency of casing or not. And then, it is shown the frequency of self excited vibration at steady-state, theoretically. Finally, the effect of physical condition of the system for those phenomena is made clear by parameter study.