Natural frequencies in coupled bending and torsion of twisted rotating and nonrotating blades : final report

Abstract : A Holzer-Myklestad type of procedure, using a matrix formulation, is developed for the determination of the natural vibration characteristics of a pretwisted rotating blade in coupled bending and torsion. The nonrotating blade is considered as a special case. Results of a limited parametric study are presented. It is found that in the case of the rotating blade there can be an appreciable effect of centrifugal forces in coupling the bending and torsional vibrations. In order to investigate the effects of Coriolis forces and the nonlinear effects of large angular displacements, a study is made on the basis of a simple model. Numerical results indicate that the Coriolis forces may introduce substantial phase differences between bending and torsional vibration. Limited numerical results on the nonlinear effects indicate that these effects decrease slightly the frequency of the characteristic motions as determined from a linearized analysis and introduce some coupling between the characteristic motions.