US3819009A - Duct wall acoustic treatment - Google Patents

Duct wall acoustic treatment Download PDF

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Publication number
US3819009A
US3819009A US00328713A US32871373A US3819009A US 3819009 A US3819009 A US 3819009A US 00328713 A US00328713 A US 00328713A US 32871373 A US32871373 A US 32871373A US 3819009 A US3819009 A US 3819009A
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United States
Prior art keywords
cavities
duct
neck
walls
passages
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00328713A
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English (en)
Inventor
R Motsinger
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General Electric Co
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General Electric Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
Priority to US00328713A priority Critical patent/US3819009A/en
Priority to CA189,000A priority patent/CA986735A/en
Priority to GB333174A priority patent/GB1462271A/en
Priority to IT19887/74A priority patent/IT1007136B/it
Priority to DE2404001A priority patent/DE2404001C2/de
Priority to FR7403303A priority patent/FR2216445B1/fr
Priority to JP1288374A priority patent/JPS5723280B2/ja
Priority to BE140449A priority patent/BE810492A/xx
Application granted granted Critical
Publication of US3819009A publication Critical patent/US3819009A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02C—GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS
    • F02C7/00—Features, components parts, details or accessories, not provided for in, or of interest apart form groups F02C1/00 - F02C6/00; Air intakes for jet-propulsion plants
    • F02C7/04—Air intakes for gas-turbine plants or jet-propulsion plants
    • F02C7/045—Air intakes for gas-turbine plants or jet-propulsion plants having provisions for noise suppression
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24149—Honeycomb-like
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24744—Longitudinal or transverse tubular cavity or cell

Definitions

  • noise treatment has been directed primarily toward high frequency noise, and one form of this treatment has utilized the well known Helmholtz resonator disposed in pluralities within a duct wall treatment of the engine.
  • these devices comprise a plurality of cavities connected to the duct by means of apertures which form entrances for generated sound waves.
  • Each individual cavity is capable of attenuating sound wave propagation within discrete frequency bands by means of energy dissipation within the cavity resulting from pressure losses of the flow passing in and out of the cavities.
  • the frequency bands-within which an individual cavity is effective are closely limited about a resonant frequency which is established by the Helmholtz resonator equation:
  • duct walls have been treated with discrete layers of different sized Helmholtz cavities separated from the duct and from one another by thin porous face sheets so that sound of higher frequency is retained within the duct-bordering smaller cavities, while lower frequency sound penetrates these smaller cavities and is dissipated within radially outward larger cavities.
  • this approach suffers from affects on overall duct thickness.
  • Duct length is another parameter which is preferably minimized in most gas turbine engines. Hence, this treatment also has met with limited usefulness.
  • the present invention deals successfully with the contemporaneous problems of wide frequency range sound suppression, duct length minimization, and nacelle thickness minimization.
  • the basic concepts involved can be elucidated with reference to the foregoing Helmholtz resonatorequation. Referring to the denominator of the radial function, it can be seen that resonator frequency (W is inversely proportional to the product of the effective length (l') of the resonator neck and the contained volume (V) in the resonator. Hence, elongation of the neck passage permits reduction of the cavity volume without affecting resonant frequency.
  • the present invention makes use of this concept by disposing a plurality of neck passages within an acoustic panel in such a way as to provide a plurality of relatively large volume cavities for the suppression of low frequency sound along with smaller volume cavities without the necessity of overly lengthening or thickening the panel itself. This is accomplished, in general, by utilizing structure already present in the panel to form various cavities and neck passages.
  • the present concept permits combining several different size cavities into a configuration which inherently provides a variety of neck lengths.
  • this invention provides for the use of several different effective frequency suppression bands without the necessity of adding substantially to the length or thickness of the duct which must be treated.
  • a sound suppressing panel comprising a plurality of cavities having a variety of cavity volumes and spaced from the duct within the panel by a variety of distances.
  • a plurality of interspersed, various length neck passages is provided for providing substantially direct communication between the various cavities and the duct.
  • the neck passages vary in length depending upon the disposition of the associated cavities within the panel, and their separation from the duct.
  • wall portions defining smaller cavities also combine to form the neck passages for larger cavities. In this way, a pyramiding effect is realized whereby a broad spectrum of sound frequencies may be absorbed and dissipated within the single sound suppressing panel.
  • FIG. 1' is a cross-sectional view of a simplified gas turbine engine
  • FIG. 2 is an enlarged cross-sectional view of a portion of the treated duct wall of FIG. 1 according to the present invention.
  • FIG. 3 is an enlarged cross-sectional view, similar to that in FIG. 2, but representing another embodiment of the present invention.
  • the simplified gas turbine engine designated generally includes an annular duct inlet 12, a bladed fan 14, a compressor 16, combustion chambers 18, and turbine along with exhaust nozzle .22.
  • This engine operates in a fashion similar to typical engines of this variety. Atmospheric air enters inlet 12 to the left in FIG. 1 tobe operated upon and compressed by fan 14 and compressor 16, a portion of the flow passing through a fan duct 24 and the remainder through the compressor 16 and into conbustors 18.
  • the air is mixed with fuel and ignited, whereupon rapid expansion of the fuel occurs and a high velocity stream of products of combustion exits the combustors to the right and engages the rotatable bladed stages of turbine 20 to impart torque thereto for the operation of fan 14 and compressor 16.
  • the gas stream exiting the turbine 20 is combined with the fan stream within fan duct 24 and expelled through the exhaust nozzle 22 to provide a substantial thrust toward the left in the Figure.
  • v Objectionable engine noise has been determined to be generated in several portions of the engine: the fan blades rotating at high tip velocities generate a broad spectrum of noise frequencies; compressors and turbines generally high'frequency noise; and the combustors are also a noise source.
  • the present invention provides a sound suppressing treatment for the wall 26 defining the duct 12 (or for similar duct surfaces throughout the engine).
  • FIG. 2 a first embodiment of the present invention is depicted in application to wall 26, as an example of typical wall applications.
  • This figure shows an enlarged view of the duct wall 26 whereupon a panel 27 incorporating a plurality of Helmholtz resonator type cavities is disposed.
  • Small cavities 30 having a first predetermined volume and disposed immediately adjacent the duct 12 are partially defined by a number of radially extending side walls 32 and an axially extending backing wall 34.
  • Each of the first cavities 30 is separated from the duct by means of the thickness of axially extending duct wall 26, and in which a plurality of apertures 36 are disposed.
  • Each of the small cavities 30 opens directly into the duct 12 by means of one of the apertures 36.
  • a second plurality of cavities 40 is also incorporated into the panel 27.
  • the cavities 40 have a second predetermined volume larger than the volume of cavities 30.
  • Each cavity 40 is partially defined by an axially extending wall 44, along with walls 34 (which also bounds cavities 30, as stated).
  • walls 34 which also bounds cavities 30, as stated.
  • the previously mentioned walls 32 and radially extending walls 42 are common walls to the extent of the length of walls 32. Such double usage of walls results in substantial weight savings due to the absence of a requirement for adding redundant walls.
  • Each cavity 40 is connected to duct 12 by means of one (or more, as above) radially extending neck passage 46 providing substantially-direct communication between the cavity 40 and the duct 12. It can be seen from the figure that neck passages 46 are defined by opposed pairs of the walls 32 of adjacent first cavities 30. Hence, a further weight savings.
  • the interrelationship between the first and second plurality of cavities 30 and 40, respectively, is such that cavities 30 are disposed generally in a layer (owing to axial colinearity of walls 34) which is disposed to the radial interior of a second layer of cavities 40 (produced by a similar colinearity of walls 44).
  • Each cavity 40 in this first embodiment, substantially circumscribes at least one pair of cavities 30.
  • the cavities 30 lie substantially between the duct and cavities 40.
  • each cavity for sound waves.
  • the entrance with respect to each of cavities 30 is an aperture 36.
  • the entrances to. cavities 40 are neck passages 46. Axially, it can be seen that the first and second neck passages 36 and 46, respectively, are substantially interspersed with respect to one another so that sound waves occurring within a given length of duct 12 will encounter both varities of neck passages and enter both types of cavities.
  • the gas turbine engine noise emanating forward through duct 12 comprises a plurality of frequencies.
  • the sound dissipation capacities of individual Helmholtz resonator type cavities are narrowly limited about predetermined resonant frequencies, determined, in part, by the product (lV) of cavity volume and neck passage length.
  • a third plurality of cavities 50 are defined by a number of radially extending walls 52 and an axially extending wall 54 along with a second weight-saving usage of walls 44.
  • a neck passage 56 is defined by side walls 42 of adjacent cavities 40.
  • the volume of cavities 50 is larger than the volume of cavities 40 (which is in turn larger than the volume of cavities 30).
  • the length of neck passages 56 is.longer than, that of neck passages 46 (which isin turn longer than that of neck passages 36).
  • the product lV is largest with respect to cavities 50, smaller with respect to cavities 40 and smallest with respect to cavities 30.
  • the entrances to neck passages 36, 46 and 56 are all interpersed with one another.
  • the acoustic panal of the present invention makes possible the treatment of wide ranges of sound frequencies along a single length of acoustic panel without the necessity for adding additional lengths.
  • the utilization of the cavity walls within the panel 27, to both define individual cavities as well as the various walls and neck passages for other cavities results in a lightweight configuration.
  • the fact that the neck passage length for the lower frequency cavities are relatively long results in an ability to treat low sound frequencies with relatively small cavity volumes. (This fact can be appreciated by recalling that resonant frequency is a function of the product of neck passage length and cavity volume).
  • the overall panel thickness is advantageously minimized.
  • this first embodiment'of the present invention results in a duct wall sound suppressing treatment including an intermixed plurality of resonant cavities having non-uniform volumes, and a plurality of neck passages providing substantially direct communication between the duct and the cavities. Furthermore, preselected of the cavities are spaced from the duct; and the neck passages are of non-uniform length, preselected longer neck passages being associated with cavities at relatively greater distances from the duct. The larger volume individuals of the cavities are associated with the longer neck passages in order to maximize the product of 1 'V, and hence to achieve effective sound treatment of low frequency sound waves.
  • FIG. 3 a second embodiment of the present invention is disclosed.
  • this embodiment is identical with the first but for the addition of a porous face sheet 58.
  • the face sheet partially defines duct 12 and enhances the aerodynamic efficiency of the duct as contrasted with the plurality of neck passage openings in FIG. 2.
  • the neck passages 36, 46 and 56 terminate at the face sheet, but the nature of the sheet is such that sound waves freely pass therethrough for effective sound wave entrance to the various cavities 30, 40 and 50. In other words, substantially direct communication between the cavity interiors and the duct is maintained despite the application of face sheet 58.
  • the embodiment of FIG. 3 performs substantially similarly to that of FIG. 2.
  • the interrelationship between the cavities disclosed in the preceding embodiments can be substantially varied without varying the overall operation of the acoustic panel.
  • further cavities and associated neck passages can be interspersed having different l'V products and thus, difierent frequency range characteristics.
  • the relative volumes of the various cavities could be adjusted with similar adjustments to neck passage lengths while maintaining characteristic frequency suppression. This would allow the panel to be narrowed and elongated or shortened and thickened depending upon appropriate limitations in given applications, due to the equalizing interaction between neck passage length and-volume in the l 'V product.
  • Such variations and those similar to it are intended to be interpreted as falling within the present invention.
  • a sound suppressing panel for use in ducts comprising:
  • a sound suppressing panel for use in ducts comprising:
  • first plurality of cavities having predetermined first volumes; a second plurality of cavities having predetermined second volumes; first means for providing substantially direct communication between said first cavities and said duct; and second means for providing substantially direct communication between said second cavities and said duct; said first and second cavities separated from the duct, the first cavities by a smaller distance than the sec ond cavities; said first means including a plurality of first neck passages, and said second means including a plurality of second neck passages, the second neck passages of greater length than the first; wherein the plurality of second neck passages is interspersed among the plurality of first neck passages; and further including a third plurality of cavities having predetermined third volumes, the third cavities separated from the duct, and a plurality of third neck passages for providing substantially direct communication between the third cavities and the duct; wherein said first cavities include first walls of predetermined first length, opposed pairs of said first walls partially defining said second neck passages; and said second cavities include second walls of predetermined second length, opposed pairs of said second walls partially defining said third neck passages

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
  • Exhaust Silencers (AREA)
  • Building Environments (AREA)
  • Pipe Accessories (AREA)
  • Structures Of Non-Positive Displacement Pumps (AREA)
  • Duct Arrangements (AREA)
US00328713A 1973-02-01 1973-02-01 Duct wall acoustic treatment Expired - Lifetime US3819009A (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
US00328713A US3819009A (en) 1973-02-01 1973-02-01 Duct wall acoustic treatment
CA189,000A CA986735A (en) 1973-02-01 1973-12-27 Duct wall acoustic treatment
GB333174A GB1462271A (en) 1973-02-01 1974-01-24 Sound suppressing panels for ducts
IT19887/74A IT1007136B (it) 1973-02-01 1974-01-28 Insonorizzazione di parete di condotto particolarmente per turbomotori a gas
DE2404001A DE2404001C2 (de) 1973-02-01 1974-01-29 Schallunterdrückungsverkleidung für Strömungskanäle von Gasturbinentriebwerken
FR7403303A FR2216445B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1973-02-01 1974-01-31
JP1288374A JPS5723280B2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1973-02-01 1974-02-01
BE140449A BE810492A (fr) 1973-02-01 1974-02-01 Dispositif d'extinction acoustique

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US00328713A US3819009A (en) 1973-02-01 1973-02-01 Duct wall acoustic treatment

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US3819009A true US3819009A (en) 1974-06-25

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US00328713A Expired - Lifetime US3819009A (en) 1973-02-01 1973-02-01 Duct wall acoustic treatment

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US (1) US3819009A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
JP (1) JPS5723280B2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
BE (1) BE810492A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
CA (1) CA986735A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
DE (1) DE2404001C2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
FR (1) FR2216445B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
GB (1) GB1462271A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
IT (1) IT1007136B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)

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Also Published As

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FR2216445A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1974-08-30
JPS49106111A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1974-10-08
FR2216445B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1980-06-27
DE2404001C2 (de) 1983-10-27
JPS5723280B2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1982-05-18
GB1462271A (en) 1977-01-19
IT1007136B (it) 1976-10-30
CA986735A (en) 1976-04-06
DE2404001A1 (de) 1974-08-08
BE810492A (fr) 1974-05-29

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