초록 ▼

An acoustic lining for a flow duct has a first perforate skin fixed to an underlying sound-absorbing layer. The first perforate skin is overlain by a second perforate skin which forms the wall of the flow duct. One of the skins is relatively moveable in a sliding sense with respect to the other skin

An acoustic lining for a flow duct has a first perforate skin fixed to an underlying sound-absorbing layer. The first perforate skin is overlain by a second perforate skin which forms the wall of the flow duct. One of the skins is relatively moveable in a sliding sense with respect to the other skin so as to vary the acoustic impedance of the duct wall as the perforations in the respective skins slide into and out of registration with each other. This enables the acoustic impedance of the duct wall to be varied to suit the flow and noise conditions prevailing in the duct and so obtain optimum noise attenuation in the duct, which may be the intake duct of a turbofan aeroengine.

대표청구항 ▼

An acoustic lining forming at least a part of a peripheral wall of a flow duct in a fluid flow machine, said acoustic lining, while in situ as said at least a part of said peripheral wall absorbing sound without obturating sound and flow of fluid and having acoustic impedances capable of being varie

An acoustic lining forming at least a part of a peripheral wall of a flow duct in a fluid flow machine, said acoustic lining, while in situ as said at least a part of said peripheral wall absorbing sound without obturating sound and flow of fluid and having acoustic impedances capable of being varied to suit changing flow and noise conditions in said duct and comprising: a perforate sound permeable facing skin; a further perforate sound permeable skin, said perforate facing skin overlying said further perforate skin; and said perforate facing skin and said further perforate skin being relatively movable with respect to each other in a contact or non-contact sliding sense to vary said acoustic impedance to suit the changing flow and noise conditions in said duct.