Patent ID: 7992674

Claim:
A fan system with dipole flow driven resonators for attenuation of noise, the system comprising: a rotor supported for rotation about a fan axis, the rotor having a central hub and a plurality of blades each extending outwardly from the hub to a tip, the rotor blades defining a rotor plane perpendicular to the fan axis; a first acoustic resonator having an opening disposed on a first side of the rotor plane; and a second acoustic resonator having an opening being disposed on a second side of the rotor plane; the acoustic resonators being configured and positioned so as to be flow driven by the tips of the blades as the tips pass the openings of the resonators, the resonators being tuned such that the resonators respond acoustically as a flow driven dipole sound source operable to at least partially reduce a blade pass or higher harmonic frequency tone in an upstream and a downstream direction simultaneously, the first and second acoustic resonators being tuned to be generally 180 degrees out of phase with one another and to radiate generally the same magnitude of energy so as to respond acoustically as the dipole sound source.