A Spectral Formulation for Structural/Aeroelastic Modeling of Curved-Axis Rotor Blades

The aim of this work is the development of a numerical solver for structural and aeroelastic analysis of rotor blades with advanced geometry, like those with tip sweep and anhedral angles. The mathematical formulation presented is based on a beam-like model assumption, suited for numerical integration via modal approach. It is valid for slender, homogeneous, isotropic, twisted blades with curved elastic axis, although the extension to composite material blades is straightforward. For aeroelastic applications, the distributed loads include the presence of the aerodynamic loads predicted by a simple quasi-steady, sectional theory, but more accurate, complex aerodynamic formulations could be coupled with the structural dynamics model outlined. After application of a second order approximation scheme, the final nonlinear equations of motion are able to predict the dynamics of blades subject to moderate displacements. The model is conceived as a sequence of relations that yield the loads to be included directly in the equilibrium equations of sectional moments and allows both response and stability analyses. Comparisons with results from FEM analyses will be shown for validation, along with a parametric analysis on blade tip sweep and anhedral angles influence on aeroelastic stability.