The influence on coupling vibrations among shaft-torsion and blade-bending coupling vibrations of a rotor system with grouped blades was investigated analytically. The natural frequencies and the mode shapes of the system were solved with five- and six-blade cases used as examples. First, numerical results showed how the natural frequencies varied with the wire stiffness and the lacing wire mistuned. The diagrams of the coupling mode shapes were drawn. From the results, it was found that lacing wire did not affect the SB (shaft-blades) coupling modes, but the BB (inter-blades) modes were indeed affected by the lacing wire. At wire stiffness k*=10, the repeated BB modes split into more distinct modes. The BB modes were of (N-1) / 2 and N / 2 multiplicity for odd and even numbered blades. When the system has a mistuned lacing wire, it splits the BB modes and will once more have (N-1) frequencies. In the rotation effect, whatever tuned or mistuned, the lacing wires did not affect the instability. That means the instability preexisted due to rotation and was not induced by lacing wires.
Shaft-Torsion and Blade-Bending Coupling Vibrations in a Rotor System with Grouped Blades
