Simultaneous Balancing of Rigid Body Modes and Bending Modes for Flexible Rotors

Abstract

On a balancing problem of flexible rotors, unbalance of rigid body modes are eliminated with a dynamic balancing machine and each bending mode is balanced in the field with the rotor mounted in its own bearings. Though rigid body modes and bending modes are considered separately on usual steps, simultaneous balancing must be needed for very flexible rotors on which rigid body modes and bending modes are strongly coupled. In this paper, we propose the modal balancing method in which both rigid body modes and bending modes are considered simultaneously. By using this method and a feature of (N+2) plane balancing, flexible rotors can be balanced on a dynamic balancing machine without an expensive field balancing. In experiments, a flexible rotor is balanced by the proposed method and the ordinary influence coefficient balancing method, and the residual whirl levels under these methods are discussed at the first critical speed.