Reduced Order Model for a Two Stage Gas Turbine Including Mistuned Bladed Disks and Shaft Interaction

Abstract

A number of previous works have suggested that in some cases the interaction between shaft and bladed disk modes could significantly modify the dynamics of the whole assembly i.e. the bladed disks mounted on a flexible shaft. This paper presents the application of a previously published reduced-order modeling technique to the dynamical modeling of a real two stage gas turbine, including the bladed disks and the shaft. In the resulting reduce order model, mistuning is included in the bladed disk models and the shaft is modeled using beam finite elements according to the classical rotordynamic approach. Generation of finite element parent model for the real turbine is presented and discussed as well as simplifications used in order to generate the reduced order model. Comparisons are made between the reduced model and the full finite element solution for free response frequencies and mode shapes in order to assess the methodology and to evaluate the impact of simplifying hypothesis considered in model generation. Finally, this work also shows interaction between shaft modes and bladed disk modes, therefore confirming that stage independent analysis might not be adequate for predicting the global dynamic response of some turbomachinery rotors.