Coupled Bending-Torsion Vibrations of Rotating Blades Free

This paper presents analytical and experimental investigations to determine the coupled bending-torsion natural frequencies of cantilever blades mounted on a rotating disk. Galerkin method is applied to solve the coupled differential equations of motion for an aerofoil cross-section blade with asymmetry about only one principal axis. The blade is considered to be mounted with the axis of symmetry in the plane of disk rotation. Results obtained are presented in non-dimensional form, showing the effects of rotation, disk radius, and asymmetry on the lowest three-coupled bending and lowest three-coupled torsion frequencies. An experimental rig is designed and fabricated to test rotating blades using piezoelectric crystals to excite the blades and also to pick up the response. The theoretical results are shown to be in good agreement with experimental observations.