A Study of the Effect of Geometry Changes on the Structural Stiffness of a Composite D-Spar

The paper examines the impact of varying two geometric cross-section parameters of an advance composite D-spar on its structural stiffness. For a given blade topology, the orientation of the D-spar web with respect to the beam axis and the distance of the D-spar web from the leading edge of the blade have been selected here as the variables of study, as they govern the elastic properties of the composite cross-section. A code has been developed to calculate the matrix terms of the Euler-Bernoulli cross-sectional stiffness utilizing the closed form expressions of the structural properties formulated by assuming both Thin-Walled composite Beam theory (TWB) and Classical Laminate Theory. The code has been validated through the Variational Asymptotic Beam Sectional analysis (VABS) for the cross-sectional stiffness matrix. Two cases have been studied for a quasi-isotropic laminate D-spar. The first is for a symmetric airfoil, whereas the second is for an unsymmetrical airfoil. The variation of the stiffness parameters for the quasi-isotropic D-spar including the coupling parameters has been visualized into parametric maps. The paper also examines the impact that these geometric variables have on the stiffness-to-mass ratio to show that along with the ply orientations they play a major role in the aeroelastic tailoring and structural optimization of a composite blade.