Structural systems having cyclic symmetry are characterized by double modes. An example of such a system is the rotating stage of turbomachines, generally known as a bladed disk. In previous studies by various workers, it has been customary to consider only one bladed disk in isolation. In an actual engine, several bladed disks are interconnected through the residual flexibility of the shaft. In this paper, the effect of inter-stage coupling on the modal characteristics of turbine blades is investigated. A multiplicity of the double modes within a narrow spectral band is shown to exist when all the bladed disks are tuned. If the blades in the engine are completely mistuned, then every double mode is split into a pair of close modes. The high modal density resulting from such splitting leads to a considerable interference among the system modes, to an extent much more complicated than the case of an isolated bladed disk.
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