Geometrically Exact Aeroelastic Stability Analysis of Composite Helicopter Rotor Blades in Hover by Updated VABS

Accurate methods for geometrically exact aeroelastic stability analysis of composite helicopter rotor blades in hover have been proposed in this paper. The aeroelastic model is established by using the geometrically exact beam theory and the updated variational asymptotic beam sectional (VABS) analysis which can cover the effect of initial twist and curvatures and calculate accurately the structural properties of the blade cross section with arbitrary shape and material distribution. The Peters finite state airloads theory and Peters-He finite state dynamic wake model are adopted to calculate the three-dimensional unsteady airloads. To ensure the calculation accuracy of the geometrically exact aeroelastic stability of the blades, the time domain method based on the finite element spatial discretization, Newmark numerical integration and Newton-Raphson methods to calculate the aeroelastic responses of blades and the moving-block analysis to extract the regressive lag mode damping from the blade transient responses are established. The accuracy of the proposed methods is verified by experimental results. The investigation results indicate that the transverse shear deformation and initial curvatures of the blades have significant effects on the aeroelastic stability of the hingeless composite rotors in hover. The rotor blades of helicopter are the lift components of helicopter. Under the flight conditions of high speed, heavy load, and large maneuvering, the composite blades will produce large aeroelastic deformation and aeroelastic instability. Therefore, it is necessary to establish an accurate aeroelastic analysis method for composite blades of helicopters. In this paper, an accurate method for geometrically exact aeroelastic stability analysis of composite rotor blades of a helicopter in hover has been proposed with applications to sophisticatedly treat the anisotropy material properties, arbitrary cross-sectional shape and material distributions, and initial twist, and material distributions and initial twist and curvatures of composite rotor blades of a helicopter. The cross-sectional structural properties and large deflections of the blades under applied forces and moments can be calculated accurately and efficiently. The presented method may also be applied to the analysis of turbine blades, aircraft wings, and many other engineering structures with beam-like geometries and has potential applications in the structural and aeroelastic modeling of these beam-like structures.