On the Dynamic Response of Axially Coupled Turborotors

Abstract

An analytical investigation of the effect of coupling characteristics on the response of axially coupled sets of turborotors is presented. The results of this investigation are based on transfer matrix techniques which utilize a generalized machine element matrix and coupling fixity matrix. Disc inertia, gyroscopic effects, and both shaft as well as coupling orthotropy are included in this study. An illustrative example, utilizing two axially coupled modified Prohl rotors, demonstrates that the nature of the coupling has a significant effect on the response characteristics of the rotor set. This is accomplished by varying coupling fixity from zero to infinity in an isotropic as well as orthotropic manner. As a consequence, this result implies that the coupling must be taken into account throughout the entire mechanical design effort devoted to the rotor system. In particular, the coupling must be considered when writing balancing specifications and during actual balancing of the rotor set. Finally, it is shown that the axial coupling of turborotors can result in the unloading of particular bearings of the turborotor set at discrete speeds. Such unloading may initiate journal instabilities that are known to be associated with light loading conditions.