Experimental-Cum-Numerical Evaluation Of Structural Properties And Vibrational Spectra Of New Smart Twisting Active Rotor Blades

Abstract

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