Attenuation of noise from air or gas intake ducts, more especially in aircraft jet turbine engines

Claim 2

In and for an intake duct of a machine fed with gaseous fluid, a device for attenuating the noise which spreads towards and emerges from the upstream end of the duct, said device comprising: a structure disposed in said duct incorporating a multiplicity of passages, each having an initial convergent region in which the cross-sectional area of the passage decreases to form a sonic-speed throat followed by a divergent region in which the cross-sectional area of the passage re-expands, whereby an intake of gaseous fluid entering the duct at subsonic speed is subdivided by said structure into a corresponding multiplicity of streams which accelerate to sonic speed in said convergent region and then expand downstream thereof in said divergent region, and means adjacent the outlet of each said passage for effecting recompression of the stream emerging therefrom to change the downstream flow into a subsonic flow.

Claim 3

A device according to claim 1 wherein the passages are in the form of a multiplicity of annular slots.

Claim 4

A device according to claim 1 wherein said structure has a downstream face extending generally transversely to the duct axis and said downstream face includes a multiplicity of solid surface regions surrounding the outlet of each of the passages therein to produce shock waves in the streams emerging from such outlets and thereby effect recompression of such streams.

Claim 5

In and for an intake duct of a machine fed with gaseous fluid, a device for attenuating the noise which spreads towards and emerges from the upstream end of the duct, said device comprising: a structure disposed in said duct incorporating a multiplicity of passages, each having an initial convergent region in which the cross-sectional area of the passage decreases to form a sonic-speed throat followed by a divergent region in which the cross-sectional area of the passage re-expands, whereby an intake of gaseous fluid entering the duct at subsonic speed is subdivided into a corresponding multiplicity of streams which accelerate to sonic speed in said convergent region and then expand downstream thereof in said divergent region, and a multiplicity of additional throat-like passages each having in succession a convergent and a divergent region, each such passage being located immediately downstream of the outlet of the corresponding first passage to receive the stream emerging therefrom to form a further sonic-speed throat in said further passage.

Claim 6

In and for an intake duct of a machine fed with gaseous fluid, a device for attenuating the noise which spreads towards and emerges from the upstream end of the duct, said device comprising: a structure disposed in said duct incorporating a multiplicity of passages, each having an initial convergent region in which the cross-sectional area of the passage decreases to form a sonic-speed throat followed by a divergent region in which the cross-sectional area of the passage re-expands, whereby an intake of gaseous fluid entering the duct at subsonic speed is subdivided into a corresponding multiplicity of streams which accelerate to sonic speed in said convergent region and then expand downstream thereof in said divergent region, and a multiplicity of additional throat-like passages each having in succession a convergent and a divergent region, each such passage being located immediately downstream of the outlet of the corresponding first passage to receive the stream emerging therefrom to form a further sonic-speed throat in said further passage.

Claim 7

A device according to claim 4 wherein the structure comprises two closely joined plates in which are respectively arranged the first convergent-divergent passages and the further convergent-divergent passages.

Claim 8

A device according to claim 4 wherein the passages are so arranged that the downstream termination of the divergent regions are contiguous.

Claim 9

In and for an intake duct of a machine fed with gaseous fluid, a device for attenuating the noise which spreads towards and emerges from the upstream end of the duct, said device comprising: a structure disposed in said duct incorporating a multiplicity of passages, each having an initial convergent region in which the cross-sectional area of the passage decreases to foRm a sonic-speed throat followed by a divergent region in which the cross-sectional area of the passage re-expands, whereby an intake of gaseous fluid entering the duct at subsonic speed is subdivided into a corresponding multiplicity of streams which accelerate to sonic speed in said convergent region and then expand downstream thereof in said divergent region, and a multiplicity of convergent passages each located immediately downstream of the corresponding convergent-divergent passage to receive the stream emerging therefrom and terminating at its downstream end in a sonic-speed discharge orifice for the stream.

Claim 10

In and for an intake duct of a machine fed with gaseous fluid, a device for attenuating the noise which spreads towards and emerges from the upstream end of the duct, said device comprising: a structure disposed in said duct incorporating a multiplicity of passages, each having an initial convergent region in which the cross-sectional area of the passage decreases to foRm a sonic-speed throat followed by a divergent region in which the cross-sectional area of the passage re-expands, whereby an intake of gaseous fluid entering the duct at subsonic speed is subdivided into a corresponding multiplicity of streams which accelerate to sonic speed in said convergent region and then expand downstream thereof in said divergent region, and a multiplicity of convergent passages each located immediately downstream of the corresponding convergent-divergent passage to receive the stream emerging therefrom and terminating at its downstream end in a sonic-speed discharge orifice for the stream.

Claim 11

A device according to claim 7 wherein the structure comprises two closely joined plates in which are respectively arranged the convergent-divergent passages and the convergent passages.

Claim 12

In and for an intake duct of a machine fed with gaseous fluid, a device for attenuating the noise which spreads towards and emerges from the upstream end of the duct, said device comprising: a structure disposed in said duct incorporating a multiplicity of passages, each having an initial convergent region in which the cross-sectional area of the passage decreases to form a sonic-speed throat followed by a divergent region in which the cross-sectional area of the passage reexpands, whereby an intake of gaseous fluid entering the duct at subsonic speed is subdivided by said structure into a corresponding multiplicity of streams which accelerate to sonic speed in said convergent region and then expand downstream thereof in said divergent region, and means adjacent the outlet of each said passage for effecting recompression of the stream emerging therefrom to change the downstream flow into a subsonic flow, wherein the passages form a multiplicity of perforations through a generally solid plate, said perforations being distributed regularly to form a mesh-like pattern.

Claim 13

In and for an intake duct of a machine fed with gaseous fluid, a device for attenuating the noise which spreads towards and emerges from the upstream end of the duct, said device comprising: a structure disposed in said duct incorporating a multiplicity of passages, each having an initial convergent region in which the cross-sectional area of the passage decreases to form a sonic-speed throat followed by a divergent region in which the cross-sectional area of the passage reexpands, whereby an intake of gaseous fluid entering the duct at subsonic speed is subdivided by said structure into a corresponding multiplicity of streams which accelerate to sonic speed in said convergent region and then expand downstream thereof in said divergent region, and means adjacent the outlet of each said passage for effecting recompression of the stream emerging therefrom to change the downstream flow into a subsonic flow, wherein the passages form a multiplicity of perforations through a generally solid plate, said perforations being distributed regularly to form a mesh-like pattern.