Analytical Prediction of the Rotor Dynamics for Advanced Geometry Blades

This paper is focusing on the specific torsional behavior of advanced blade planforms featuring large sweep offsets over a significant part of span. Using two complementary data bases, first the ROSOH soft-in-torsion rotor with removable tips and, second, the dynamically scaled ORPHEE/HLR blades, the validatity of numerical analysis is addressed and potential model refinements are tested. Both the mode frequency diagram and aeroelastic stability are shown to be very sensitive to unsteady aerodynamic forces, to such a point that a complex mode approach is jugded mandatory for aero and dynamic tailoring. No general trend could be found regarding blade response, as inertial or aerodynamic forces may dominate the excitation according to aspect ratio, Lock number, or flexibility. The numerical code was generally successful in predicting subtle coupling phenomena which can hardly be isolated. With a suitable design, the ill-famed swept blades do not appear to suffer from their supposed wild and unsafe temper.