Parallel blade-vortex interaction analyses and rotor noise control synthesis

The aim of the present work is the presentation and application of a methodology for the identification of multi-cyclic higher harmonic actuation of blade pitch motion suited for the alleviation of BVI loads, and hence of BVI noise annoyance generated by helicopter main rotors in low-speed descent flight. The blade pitch actuation is defined by a feed-back control law obtained through an optimal control approach based on the minimization of a cost function. In particular, first, strong BVI phenomena occurring in the specific flight condition are simulated as equivalent two-dimensional, multi-vortex, parallel BVI problems, and then a local controller methodology is applied for the effcient identification of the closed-loop control algorithm. This control synthesis methodology is validated by application of the identified gain matrices to a realistic helicopter main rotor in descent flight, and preliminary results concerning its capability to alleviate blade loads and emitted noise are presented and discussed.