Using multibody dynamics for the stability assessment of a new double-swept rotor blade setup

Abstract

A new double-swept rotor blade setup has been assessed in frequency domain for both, dynamic stability in terms of ground resonance and aeroelastic stability related to rotor blade and rotor flutter. The blade setup is being developed for a rotor test rig and will be operated under axial inflow. Methodology is based on a multibody system which is coupled with an unsteady aerodynamic model based on Wagner's function and related enhancements for the general motion of an airfoil section considering heave and pitch motion. The simulation model uses modelling techniques for the setup of a linearized model and allows both, the investigation of ground resonance and flutter for the rig with clamped and articulated rotor blades in frequency domain. Numerical results for the two- and four-bladed rotor state dynamic stability for the setup with clamped blades within the planned rotor speed range up to 65 Hz, whilst the setup using articulated blades with lead-lag hinges indicates instability at low scale starting from a rotor frequency of 30 Hz. The aeroelastic assessment shows a small hump in the damping curves for the two-bladed rotor which is found instable at rotor speeds around 20 Hz for both rotor setups. Here, the flutter mechanism has major contributions from the backward whirl mode and flap bending modes. In contrast, the four-bladed rotor configurations do not show flutter.