Identification of Rotor Parameters

Abstract

Turbomachines do not only possess the ability to convert fluid energy into rotational energy but also the undesirable attribute that their rotors vibrate. Therefore the mechanical behaviour of the rotor has to be analysed. Whereas the inertia distribution of the shaft can be determined from its geometry, the stiffness distribution cannot be obtained easily because of jumps in the diameter of the shaft. In modeling the system consisting of a rotor on its bearings, the task which presents most difficulty is the description of the dynamical properties of the oil film used in the journal bearings. In most cases a linear model, the simplest one, is chosen. The coefficients can either he obtained experimentally from very simplified test rigs with rigid rotors or by the solution of the linearised hydrodynamic theory for oil film bearings. A second uncertainty in calculating the vibrational behaviour of the rotor of a turbomachine is due to the difficulty of specifying the true distribution of the unbalance and the initial bow of a rotor.