Broad band acoustic attenuator

Claim 2

An acoustic attenuator for heated exhaust gas from a gas turbine engine having a compressor, a combustor for heating compressed air from the compressor, turbine means driven by heated gases from the combustor, and a cylindrical exhaust duct for receiving only heated exhaust gases from said turbine means substantially without mixture with cooling fluid flow, said attenuator comprising: a plurality of open-ended cylinders extending axially within said cylindrical exhaust duct and substantially concentrically arranged within said exhaust duct, each of said cylinders having a regular pattern of equally sized apertures throughout the entire surfaces thereof, the total area of said apertures being no more than approximately one half the full surface area of said cylinders.

Claim 3

An acoustic attenuator as set forth in claim 1 further including an axially extending plug having a closed outer-end, said plug mounted centrally within the innermost of said concentric, open-ended cylinders and defining the inner boundary of said exhaust duct.

Claim 4

An acoustic attenuator as set forth in claim 2 wherein said concentric cylinders are of differing axial lengths.

Claim 5

An acoustic attenuator as set forth in claim 3, wherein said plurality of concentric cylinders comprise at least three cylinders.

Claim 6

An acoustic attenuator as set forth in claim 4, wherein the total area of said aperture is between approximately 40 percent and 50 percent of said full surface area of said cylinders.

Claim 7

An acoustic attenuator as set forth in claim 5, wherein said total open area of the apertures is approximately 44 percent.

Claim 8

An acoustic attenuator as set forth in claim 4, further comprising an air cavity type muffler extending axially and in surrounding relationship to said exhaust duct, said muffler having a perforated internal surface defining the outer boundary of said exhaust duct.

Claim 9

An acoustic attenuator as set forth in claim 7, wherein the axially shortest of said open-ended cylinders is the outermost of said concentrically arranged cylinders while the axially longest of said cylinders is said innermost cylinder.

Claim 10

An acoustic attenuator as set forth in claim 8, wherein each of said cylinders is relatively arranged to present portions thereof directly exposed to said inner surface of the muffler, said exposed portions being of preselected axial length at differing preselected radial spacings from said inner surface of the muffler whereby said exposed portions act as acoustic wave guides for reflecting acoustic wave energy in said exhaust gas flow in a direction toward said muffler internal surface for improved absorption by said muffler of said acoustic wave energy.

Claim 11

An acoustic attenuator as set forth in claim 9, wherein said cylinders are arranged with their outer ends lying substantially on a truncated conical surface having an included angle preselected in relation to the normal operating speed of said turbine means, said truncated conical surface having its apex located on the central axis of said cylindrical exhaust duct.

Claim 12

An acoustic attenuator as set forth in claim 10, wherein said preselected included angle is approximately 22.5 degrees.

Claim 13

An accoustic attenuator as set forth in claim 10, wherein said cylinders are arranged with their inner ends closely adjacent said turbine means.

Claim 14

An acoustic attenuator as set forth in claim 8, wherein said outermost cylinder is sufficiently closely spaced to said outer boundary of the exhaust duct to intercept the shear layer of boundary flow of exhaust gas at said outer boundary.

Claim 15

In a gas turbine engine generating a swirling, annularly shaped, hot, core exhaust gas flow through an axially extending, cylindrical exhaust duct: a broad band acoustic attenuator for reducing exhaust noise without introduction of cooling fluid flow into said duct, comprising a plurality of straight, axially extending, open-ended cylinders of different preselected diameters arranged concentrically in said exhaust duct and receiving only said hot core exhaust gas flow, each of said cylinders having a regular pattern of equally sized apertures, the largest diameter cylinder being sufficiently closely arranged to the internal surface of said exhaust duct to promote deswirling and mixing of said core exhaust gas flow thereat to reduce temperature gradients in said core exhaust gas flow, said apertures in each of said cylinders presenting approximately 40 percent and 50 percent open area in each of said cylinders, said cylinders being relatively thin whereby said attenuator produces minimal backpressure on said core exhaust gas flow.

Claim 16

In a gas turbine engine generating a swirling, annularly shaped, hot, core exhaust gas flow through an axially extending, cylindrical exhaust duct: a broad band acoustic attenuator for reducing exhaust noise without introduction of cooling fluid flow into said duct, comprising a plurality of straight, axially extending, open-ended cylinders of different preselected diameters arranged concentrically in said exhaust duct and receiving only said hot core exhaust gas flow, each of said cylinders having a regular pattern of equally sized apertures, the largest diameter cylinder being sufficiently closely arranged to the internal surface of said exhaust duct to promote deswirling and mixing of said core exhaust gas flow thereat to reduce temperature gradients in said core exhaust gas flow, said apertures in each of said cylinders presenting approximately 40 percent and 50 percent open area in each of said cylinders, said cylinders being relatively thin whereby said attenuator produces minimal backpressure on said core exhaust gas flow.

Claim 17

An acoustic attenuator for a gas turbine engine, comprising: an axially extending, air cavity muffler having an open internal space receiving axially flowing, swirling, heated gas from said engine, said muffler having a perforated cylindrical internal surface; and at least three open-ended cylinders mounted within said internal space concentrically to said internal surface, each of said cylinders having a regular pattern of apertures throughout the entire surface thereof, the total area of said apertures being less than approximately fifty percent of the total surface area of said cylinders, said cylinders being of different axial lengths and diameters, said lengths and diameters of the cylinders being relatively matched to present portions of each cylinder directly exposed to said internal surface of the muffler, said exposed portions being sized and arranged to act as acoustic wave guides for reflecting acoustic waves from said exhaust gas flow toward said internal surface for improved absorption of said acoustic waves by said muffler.

Claim 18

An acoustic attenuator for a gas turbine engine, comprising: an axially extending, air cavity muffler having an open internal space receiving axially flowing, swirling, heated gas from said engine, said muffler having a perforated cylindrical internal surface; and at least three open-ended cylinders mounted within said internal space concentrically to said internal surface, each of said cylinders having a regular pattern of apertures throughout the entire surface thereof, the total area of said apertures being less than approximately fifty percent of the total surface area of said cylinders, said cylinders being of different axial lengths and diameters, said lengths and diameters of the cylinders being relatively matched to present portions of each cylinder directly exposed to said internal surface of the muffler, said exposed portions being sized and arranged to act as acoustic wave guides for reflecting acoustic waves from said exhaust gas flow toward said internal surface for improved absorption of said acoustic waves by said muffler.

Claim 19

In a gas turbine engine generating a swirling, annularly shaped, hot, core exhaust gas flow through an exhaust duct having a straight, axially extending, cylindrical internal wall: at least three axially extending, open-ended, straight cylinders of different diameters disposed concentrically in said exhaust duct, each of said cylinders having a regular pattern of equally sized apertures together covering less than fifty percent of the area of each cylinder, said cylinders being of differing axial lengths and relatively arranged to present portions of each cylinder exposed to said internal wall at differing radial distances therefrom, whereby said differing exposed portions act as acoustic wave guides reflecting acoustic wave energy of said core exhaust gas flow outwardly toward said internal wall of the exhaust duct.

Claim 20

In a gas turbine engine generating a swirling, annularly shaped, hot, core exhaust gas flow through an exhaust duct having a straight, axially extending, cylindrical internal wall: at least three axially extending, open-ended, straight cylinders of different diameters disposed concentrically in said exhaust duct, each of said cylinders having a regular pattern of equally sized apertures together covering less than fifty percent of the area of each cylinder, said cylinders being of differing axial lengths and relatively arranged to present portions of each cylinder exposed to said internal wall at differing radial distances therefrom, whereby said differing exposed portions act as acoustic wave guides reflecting acoustic wave energy of said core exhaust gas flow outwardly toward said internal wall of the exhaust duct.

Claim 21

A gas turbine engine comprising: a compressor for compressing an airflow; a combustor receiving at least a portion of said airflow and heating same; turbine means driven by heated gas flow from said combustor; a cylindrical exhaust duct receiving an annularly shaped hot exhaust gas flow from said turbine means; an air cavity type muffler extending axially and in surrounding relationship to said exhaust duct, said muffler having a perforated internal surface defining the outer boundary of said exhaust duct; an axially extending plug having a closed outer end, said plug mounted concentrically within said exhaust duct and defining the inner boundary of said exhaust duct; and a plurality of open-ended cylinders of regular cylindrical configuration mounted symmetrically within said inner and outer boundaries of said exhaust duct, said cylinders having a regular pattern of equally sized apertures across substantially the entire surfaces thereof, said cylinders having inner ends disposed nearest said turbine lying in a common plane, said cylinders being of differing axial lengths with opposite outer ends disposed at differing axial distances from said turbine to present portions of each cylinder directly exposed to said internal surface of the muffler, said exposed portions being of preselected axial length and being spaced different preselected radial distances from said internal surface to act as acoustic wave guides for reflecting acoustic wave energy in said exhaust gas flow in a direction toward said muffler internal surface for improved absorption by said muffler of said acoustic wave energy.

Claim 22

A gas turbine engine comprising: a compressor for compressing an airflow; a combustor receiving at least a portion of said airflow and heating same; turbine means driven by heated gas flow from said combustor; a cylindrical exhaust duct receiving an annularly shaped hot exhaust gas flow from said turbine means; an air cavity type muffler extending axially and in surrounding relationship to said exhaust duct, said muffler having a perforated internal surface defining the outer boundary of said exhaust duct; an axially extending plug having a closed outer end, said plug mounted concentrically within said exhaust duct and defining the inner boundary of said exhaust duct; and a plurality of open-ended cylinders of regular cylindrical configuration mounted symmetrically within said inner and outer boundaries of said exhaust duct, said cylinders having a regular pattern of equally sized apertures across substantially the entire surfaces thereof, said cylinders having inner ends disposed nearest said turbine lying in a common plane, said cylinders being of differing axial lengths with opposite outer ends disposed at differing axial distances from said turbine to present portions of each cylinder directly exposed to said internal surface of the muffler, said exposed portions being of preselected axial length and being spaced different preselected radial distances from said internal surface to act as acoustic wave guides for reflecting acoustic wave energy in said exhaust gas flow in a direction toward said muffler internal surface for improved absorption by said muffler of said acoustic wave energy.

Claim 23

In a gas turbine engine generating a swirling, hot core exhaust gas flow from an annularly shaped opening about a central plug, a broad band acoustic attenuator comprising: an axially extending cylindrical exhaust pipe secured to said engine and surrounding said opening for receiving only said hot core exhaust flow, said pipe having cylindrical outer and inner walls respectively having diameters greater than and approximately equal to the outer diameter of said annularly shaped opening, said inner wall being perforated; a plurality of baffles extending perpendicularly between said inner and outer walls of said exhaust pipe to present acoustically attenuating, separate air cavities for absorbing acoustical wave energy from said core exhaust flow through said perforated inner wall; a first open-ended cylinder of first preselected axial length mounted to said exhaust pipe concentrically within said inner wall, said first cylinder having a first diameter slightly less than said diameter of the inner wall to promote interception of the shear layer of core exhaust flow adjacent said inner wall, said first cylinder having a regular pattern of equally sized apertures having a total area of between approximately forty and fifty percent of the area of said first cylinder, said apertures promoting turbulence and deswirling of said core exhaust flow for reducing temperature gradients therein; a second open-ended cylinder of second, longer axial length and second, smaller diameter than said first cylinder and mounted concentrically therewithin to present a portion of said second cylinder directly exposed to said inner wall, said second cylinder also having said regular pattern of equally sized apertures having a total area of between approximately forty and fifty percent of the area of said second cylinder, said exposed portion of the second cylinder arranged and located to reflect acoustical wave energy from core exhaust flow passing between said first and second cylinders outwardly toward said inner wall in a direction promoting absorption by said air cavities of said reflected acoustical waves; a third open-ended cylinder of third axial length longer than said second cylinder and of third diameter smaller than said second cylinder, said third cylinder mounted concentrically within said second cylinder to present a portion of said third cylinder directly exposed to said inner wall also arranged and located to reflect acoustical wave energy from core exhaust flow passing between said second and third cylinders outwardly toward said inner wall in said direction, said pattern of said equally sized apertures having a total area of between approximately forty and fifty percent of the total area of said third cylinder; and a cylindrical, closed-ended, central plug of smaller diameter and longer axial length than said third cylinder, said plug mounted concentrically within said third cylinder and having a diameter approximately equal to the inner diameter of said annularly shaped opening.

Claim 24

In a gas turbine engine generating a swirling, hot core exhaust gas flow from an annularly shaped opening about a central plug, a broad band acoustic attenuator comprising: an axially extending cylindrical exhaust pipe secured to said engine and surrounding said opening for receiving only said hot core exhaust flow, said pipe having cylindrical outer and inner walls respectively having diameters greater than and approximately equal to the outer diameter of said annularly shaped opening, said inner wall being perforated; a plurality of baffles extending perpendicularly between said inner and outer walls of said exhaust pipe to present acoustically attenuating, separate air cavities for absorbing acoustical wave energy from said core exhaust flow through said perforated inner wall; a first open-ended cylinder of first preselected axial length mounted to said exhaust pipe concentrically within said inner wall, said first cylinder having a first diameter slightly less than said diameter of the inner wall to promote interception of the shear layer of core exhaust flow adjacent said inner wall, said first cylinder having a regular pattern of equally sized apertures having a total area of between approximately forty and fifty percent of the area of said first cylinder, said apertures promoting turbulence and deswirling of said core exhaust flow for reducing temperature gradients therein; a second open-ended cylinder of second, longer axial length and second, smaller diameter than said first cylinder and mounted concentrically therewithin to present a portion of said second cylinder directly exposed to said inner wall, said second cylinder also having said regular pattern of equally sized apertures having a total area of between approximately forty and fifty percent of the area of said second cylinder, said exposed portion of the second cylinder arranged and located to reflect acoustical wave energy from core exhaust flow passing between said first and second cylinders outwardly toward said inner wall in a direction promoting absorption by said air cavities of said reflected acoustical waves; a third open-ended cylinder of third axial length longer than said second cylinder and of third diameter smaller than said second cylinder, said third cylinder mounted concentrically within said second cylinder to present a portion of said third cylinder directly exposed to said inner wall also arranged and located to reflect acoustical wave energy from core exhaust flow passing between said second and third cylinders outwardly toward said inner wall in said direction, said pattern of said equally sized apertures having a total area of between approximately forty and fifty percent of the total area of said third cylinder; and a cylindrical, closed-ended, central plug of smaller diameter and longer axial length than said third cylinder, said plug mounted concentrically within said third cylinder and having a diameter approximately equal to the inner diameter of said annularly shaped opening.