Evaluation of Structural Properties and Vibrational Spectra of New Active Twist Blades

In this work, the natural vibrational characteristics of Smart Twisting Active Rotor (STAR) II blades are examined while assessing the accuracy of the structural properties obtained using the digitally replicated model constructed based on the x-ray computed tomography (CT) scan images of the blade. The frequencies measured using various test setups established at the German Aerospace Center (DLR) are exploited for the study. The frequency measurements include the blades installed in a hover test rig at nonrotating or rotating conditions along with a bench-top test of the blade mounted vertically with clamping at the root. Detailed three-dimensional (3D) finite element (FE) models created using MSC.NASTRAN are used to verify the present analysis. The comparison results indicate good agreements for the section centroidal offsets and nonrotating frequencies of a cantilevered blade with an airfoil section. Systematic parameter studies are conducted to investigate structural dynamic aspects of the blades, which include structural load paths over the blade arm region, anisotropic couplings of composites, pitch control stiffnesses, external equipment, and flap bending stiffnesses of the blade. The impact of modeling parameters on the free vibration characteristics of the blades is discussed, and some important findings resulting from the present investigation are summarized.