Natural Frequencies and Modes Shapes of Two Mistuned Bladed Discs on the Shaft

The dynamic behaviour of a rotor consisting of two bladed discs on a solid shaft is considered. The effect of shaft flexibility on the dynamic characteristics of the bladed discs and the coupling effects between the shaft and bladed disc modes are investigated. Results show clearly the coupling effects in a bladed disc-shaft system. In this study, the global rotating mode shapes of flexible tuned and mistuned bladed disc-shaft assemblies are calculated. Rotational effects, such as centrifugal stiffening are accounted for. The gyroscopic effects are included. Calculated natural frequencies obtained from blade, bladed disc and shaft with two discs are checked to discover resonance conditions and the coupling effects. The torsional frequency of the shaft with two bladed discs is coupled with the zero nodal diameters modes of the single bladed discs. It is shown that blade mistuning strongly affects the interaction between flexible bladed discs and flexible shaft. This interaction affects the flexible bladed disc modes, and it is not restricted to the modes with zero, one and two nodal diameters.