Flap-wise loads reduction of rotor blades by embedded flap-wise absorbers

Abstract

ABSTRACTElastomeric and Fluidlastic®absorbers are proposed to be embedded in blade cavity to reduce troublesome second harmonic flap-wise blade loads of rigid rotors. A simple model of a blade with a flap-wise dynamic absorber is derived to investigate centrifugal force effects on the absorber's rotating frequency. The system's dynamic equations of motion indicate that centrifugal force has no effect on absorber's frequency under rotation. Aeroelastic simulation of the coupled rotor and absorber system based on an elastic beam model in generalised force formulation is used to explore load reduction extent and dynamic absorber behaviour. At a forward speed of 200 km/h, the elastomeric absorber reduces the second harmonic flap-wise root-bending moment by 88.8% for unacceptably large stroke; the Fluidlastic®absorber reduces the moment by 78.5% with a stroke 4.26% of blade chord length. Results indicate that placing an embedded Fluidlastic®absorber in the blade's flap-wise direction has potential for reducing load in different flight states with relatively small strokes. Increasing tuning port area ratio or Fluidlastic®absorber mass can distinctly decrease strokes without increasing loads. However, deviation from normal rotor speed significantly lowers Fluidlastic®absorber performance.