Flexible rotor blade dynamics for helicopter aeromechanics including comparisons with experimental data

Abstract

AbstractThis paper presents the development of a mathematical model for the implementation of flexible rotor blade dynamics in real-time helicopter aeromechanics applications. A Lagrangian approach is formulated for the rapid estimation of natural vibration characteristics of nonuniform rotor blades. A matrix/vector formulation is proposed for the treatment of elastic blade kinematics in the time-domain. In order to overcome the classical hurdles of time-accurate simulation and establish applicability in real-time, a novel, second-order accurate, finite-difference scheme is employed for the numerical discretisation of elastic blade motion. The proposed rotor dynamics model is coupled with a finite-state induced flow and an unsteady blade element aerodynamics model. The combined formulation is implemented in a helicopter flight mechanics simulation code. The integrated approach is deployed in order to investigate rotor blade resonant frequencies, trim control angles, oscillatory blade loads and induced vibration for a hingeless and an articulated helicopter rotor. Extensive comparisons are carried out with wind tunnel and flight test measurements, and non-real-time comprehensive analysis methods. Good agreement with measured data is exhibited considering primarily the low-frequency harmonic components of oscillatory loading. It is shown that, the developed methodology can be utilised for real-time simulation on a typical computer with sufficient modelling fidelity for accurate estimation of oscillatory blade loads.