COUPLED BENDING–BENDING–TORSION VIBRATION ANALYSIS OF ROTATING PRETWISTED BLADES: AN INTEGRAL FORMULATION AND NUMERICAL EXAMPLES

Abstract

A new approximate method is presented for the analysis of the modal characteristics of straight, pretwisted non-uniform blades corresponding to the coupled flapwise bending, chordwise bending and torsion of both rotating and non-rotating blades. An integral approach is described based on the use of Green functions (structural influence functions), which are used to develop the equations of motion. A clamped–free blade is analyzed and comparisons are made with numerical results for the literature. Several examples regarding specific aspects of the flapwise bending, coupled bending–bending, coupled bending–torsion and coupled bending–bending–torsion vibration analysis are presented. The method presented gives good results and can be used for modelling of turbomachine blades, aircraft propellers or helicopter rotor blades which may be considered as straight non-uniform beams with built-in pretwist.