Reduced Order Modeling for Multi-Stage Coupling of Cyclic Symmetric Structures

Current aircraft turbo-engines consist of multi-stage rotating bladed disks whose design depends on the linear finite element analysis of each of their components. Predicting the dynamics of the whole engine is computationally costly since the dynamic coupling of many components have to be considered. This paper presents a novel methodology used to obtain a multi-stage reduced order model when two or more cyclic symmetric stages have to be assembled. It is shown how the starting Craig-Bampton models of the stages are further reduced by approximating the motion at the inter-stage boundaries with a basis of harmonic functions. The multi-stage reduced model can be obtained when a suitable basis of harmonic functions for the two stages is found. The proposed method is particularly advantageous when the stages have a different number of sectors that lead to non-matching meshes at the inter-stage boundaries.