Refined Aeroelastic Analysis of Hingeless Rotor Blades in Hover

Abstract

The aeroelastic response and stability of hingeless rotor blades in hover are investigated using both refined structural and aerodynamic models. Finite elements based on a large deflection-type beam theory are used for structural analysis. Although the strain components in the beam element are assumed to be small compared to unity, no kinematical limitations are imposed on the magnitude of displacements and rotations. A three-dimensional aerodynamic model including compressibility effect, which is a thin lifting-surface theory based on the unsteady vortex lattice method, is applied to evaluate the aerodynamic loads. A thin lifting-surface and its wake are represented by a number of the quadrilateral vortex-ring elements. The wake geometry is prescribed from the known generalized equations. Numerical results of the steady-state deflections and the stability for the stiff in-plane rotor blade are presented. It is found that the three-dimensional aerodynamic tip-relief, unsteady wake dynamics, and compressibility effects, not predicted in the two-dimensional strip theory, play an important role in the hingeless rotor aeroelastic analysis in hover.