Toward global modelling approaches for dynamic analyses of rotating assemblies of turbomachines

It is now increasingly necessary to predict accurately, at the design stage and without excessive computer costs, the dynamic behavior of rotating parts of turbomachines, in order to be able to avoid resonant conditions at operating speeds. Classical approaches are based on different uncoupled models. For example, rotordynamics deals with the shaft behavior while bladed assemblies dynamics deals with wheels, and the possibility of interaction between those elements is generally not analyzed. In this study, the global non-rotating mode shapes of flexible bladed disc-shaft assemblies are used in a modal analysis method for calculating the dynamic characteristics (frequencies and mode shapes) of the corresponding rotating system. The non-rotating mode shapes are computed using a finite element cyclic symmetry approach. Rotational effects, such as centrifugal stiffening and gyroscopic effects, are accounted for. All the possible couplings between the flexible parts and every kind of deformations are allowed. The proposed model is applied to a thin-walled composite shaft and to a turbomolecular pump rotating assembly. The results obtained illustrate clearly some of the limitations of classical approaches. (c) 2004 Elsevier Ltd. All rights reserved.