Patent ID: 7870929

Claim:
An acoustical liner comprising: an inner barrel comprising: a perforated face sheet; a back skin comprising a plurality of perforations; and a core disposed between the perforated face sheet and the back skin; an outer barrel surrounding and spaced from the inner barrel to define a fluid-filled space therebetween; and end members configured to confine fluid contained between the inner and outer barrels to define the space between the inner and outer barrels, wherein perforations in the face sheet and a volume of fluid contained in the core provide one or more acoustical degrees of freedom, wherein the perforations defined by the back skin place the core in fluid communication with the space between the inner and outer barrels, said perforations in the back skin providing one or more additional acoustical degrees of freedom having acoustical inertia due to a thickness of the back skin in which the perforations are defined and an acoustical compliance due to the fluid communication with the space between the inner and outer barrels, and wherein the inner and outer barrels are configured to have at least one natural frequency within a first frequency range associated with fan blade flutter and at least one natural frequency within a second frequency range, different than the first frequency range, associated with fan noise at fan blade-pass frequencies.