Acoustic duct with asymmetric acoustical treatment

Claim 2

An improved noise-suppressing fan duct for an aircraft jet engine having a fan disposed within an annular fan duct air passage comprising a generally streamlined rigid fan duct with a circular cross section having an asymmetric, circumferentially discontinuous acoustic lining attached to the inner surface thereof for absorbing noise which radiates within said duct, said asymmetric acoustic lining being located on the upper portion of the circumference of said duct and being effective to alter the directivity of noise emitted from an end of said fan duct and produce an asymmetric directivity pattern characterized by preferential enhanced suppression of noise in an angular sector generally below the jet engine, wherein said asymmetric acoustic lining is approximately semicylindrical and is continuous and uninterrupted in both the axial and circumferential directions, and further including a second acoustic lining attached to the lower half of the circumference of said duct, said first-mentioned asymmetric acoustic lining having a higher sound absorption coefficient than said second acoustic lining.

Claim 3

An improved noise-suppressing fan duct for an aircraft jet engine having a fan disposed within an annular fan duct air passage comprising a generally streamlined rigid fan duct with a circular cross section having an asymmetric, circumferentially discontinuous acoustic lining attached to the inner surface thereof for absorbing noise which radiates within said duct, said asymmetric acoustic lining being located on the upper portion of the circumference of said duct and being effective to alter the directivity of noise emitted from an end of said fan duct and produce an asymmetric directivity pattern characterized by preferential enhanced suppression of noise in an angular sector generally below the jet engine, wherein said asymmetric acoustic lining is made of a fibrous acoustic material and is continuous and substantially uninterrupted in both the axial and circumferential directions, and further including a second acoustic lining attached to the lower portions of the circumference of said duct, said first-mentioned asymmetric acoustic lining having a higher sound absorption coefficient than said second acoustic lining.

Claim 4

An improved noise-suppressing fan duct for an aircraft jet engine having a fan disposed within an annular fan duct air passage comprising a generally streamlined rigid fan duct with a circular cross section having an asymmetric, circumferentially discontinuous acoustic lining attached to the inner surface thereof for absorbing noise which radiates within said duct, said asymmetric acoustic lining being located on the upper portion of the circumference of said duct and being effective to alter the directivity of noise emitted from an end of said fan duct and produce an asymmetric directivity pattern characterized by preferential enhanced suppression of noise in an angular sector generally below the jet engine, wherein said asymmetric acoustic lining is made of a fibrous acoustic material and is continuous and substantially uninterrupted in both the axial and circumferential directions, and further including a second acoustic lining attached to the lower portions of the circumference of said duct, said first-mentioned asymmetric acoustic lining having a higher sound absorption coefficient than said second acoustic lining.

Claim 5

An improved noise-suppressing fan duct for an aircraft jet engine having a fan disposed within an annular fan duct air passage comprising a generally streamlined rigid fan duct with a circular cross section having an asymmetric, circumferentially discontinuous acoustic lining attached to the inner surface thereof for absorbing noise which radiates within said duct, said asymmetric acoustic lining being located on the upper portion of the circumference of said duct and being effective to alter the directivity of noise emitted from an end of said fan duct and produce an asymmetric directivity pattern characterized by preferential enhanced suppression of noise in an angular sector generally below the jet engine, wherein said asymmetric acoustic lining is made of a fibrous acoustic material, and further including a second acoustic lining attached to the lower portion of the circumference of said duct, said second acoustic lining having provision for drainage of ingested liquids and a lower sound absorption coefficient than said first-mentioned asymmetric acoustic lining, said first-mentioned asymmetric acoustic lining and second acoustic lining in combination being circumferentially continuous, each individual lining further being continuous and substantially uninterrupted in both the circumferential and axial directions.

Claim 6

An improved noise-suppressing fan duct for an aircraft jet engine having a fan disposed within an annular fan duct air passage comprising a generally streamlined rigid fan duct with a circular cross section having an asymmetric, circumferentially discontinuous acoustic lining attached to the inner surface thereof for absorbing noise which radiates within said duct, said asymmetric acoustic lining being located on the upper portion of the circumference of said duct and being effective to alter the directivity of noise emitted from an end of said fan duct and produce an asymmetric directivity pattern characterized by preferential enhanced suppression of noise in an angular sector generally below the jet engine, wherein said asymmetric acoustic lining is made of a fibrous acoustic material, and further including a second acoustic lining attached to the lower portion of the circumference of said duct, said second acoustic lining having provision for drainage of ingested liquids and a lower sound absorption coefficient than said first-mentioned asymmetric acoustic lining, said first-mentioned asymmetric acoustic lining and second acoustic lining in combination being circumferentially continuous, each individual lining further being continuous and substantially uninterrupted in both the circumferential and axial directions.

Claim 7

A sound suppressing acoustic duct comprising an axially extending, relatively rigid hard-walled duct having attached to a portion of the periphery of the inner surface thereof a first asymmetric sound absorbing acoustic lining, a second sound absorbing acoustic lining attached to the remaining portion of the periphery of the inner surface of said duct, said first and second acoustic linings in combination being peripherally continuous and functioning to absorb sound which radiates longitudinally through said duct and is reflected internally, each of said acoustic linings individually being continuous and substantially uninterrupted in both the axial and peripheral directions, said first acoustic lining further having a higher sound absorption coefficient than said second acoustic lining, said first asymmetric sound absorbing lining being peripherally located at any desired peripheral location to alter the directivity of sound emitted from an end of said duct and produce an asymmetric directivity pattern characterized by preferential enhanced suppression of sound in a preselected angular sector.

Claim 8

A sound suppressing acoustic duct comprising an axially extending, relatively rigid hard-walled duct having attached to a portion of the periphery of the inner surface thereof a first asymmetric sound absorbing acoustic lining, a second sound absorbing acoustic lining attached to the remaining portion of the periphery of the inner surface of said duct, said first and second acoustic linings in combination being peripherally continuous and functioning to absorb sound which radiates longitudinally through said duct and is reflected internally, each of said acoustic linings individually being continuous and substantially uninterrupted in both the axial and peripheral directions, said first acoustic lining further having a higher sound absorption coefficient than said second acoustic lining, said first asymmetric sound absorbing lining being peripherally located at any desired peripheral location to alter the directivity of sound emitted from an end of said duct and produce an asymmetric directivity pattern characterized by preferential enhanced suppression of sound in a preselected angular sector.

Claim 9

A sound suppressing acoustic duct according to claim 4 wherein said duct is an aircraft jet engine fan duct and at least said first acoustic lining is made of a fibrous acoustic material.

Claim 10

A sound suppressing acoustic duct comprising an axially extending, relatively rigid duct having a hard-walled inner surface into which is recessed an aTtached acoustic lining for preferential side lobe suppression comprised by a pair of opposing sound absorbing strips for absorbing sound which radiates longitudinally through said duct and is reflected internally, each of said sound absorbing strips being made of the same acoustic material and each being continuous and substantially uninterrupted in both the axial and peripheral directions. said pair of opposing sound absorbing strips being peripherally spaced from one another and peripherally located and dimensioned to obtain preferential enhanced side lobe suppression of the sound emitted from an end of said duct.

Claim 11

A sound suppressing acoustic duct comprising an axially extending, relatively rigid duct having a hard-walled inner surface into which is recessed an aTtached acoustic lining for preferential side lobe suppression comprised by a pair of opposing sound absorbing strips for absorbing sound which radiates longitudinally through said duct and is reflected internally, each of said sound absorbing strips being made of the same acoustic material and each being continuous and substantially uninterrupted in both the axial and peripheral directions. said pair of opposing sound absorbing strips being peripherally spaced from one another and peripherally located and dimensioned to obtain preferential enhanced side lobe suppression of the sound emitted from an end of said duct.