GB2204916A - Gaseous flow silencer - Google Patents

Gaseous flow silencer Download PDF

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Publication number
GB2204916A
GB2204916A GB08711767A GB8711767A GB2204916A GB 2204916 A GB2204916 A GB 2204916A GB 08711767 A GB08711767 A GB 08711767A GB 8711767 A GB8711767 A GB 8711767A GB 2204916 A GB2204916 A GB 2204916A
Authority
GB
United Kingdom
Prior art keywords
silencer
active
casing
gas stream
silencer according
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.)
Granted
Application number
GB08711767A
Other versions
GB2204916B (en
GB8711767D0 (en
Inventor
Colin David Lyle
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
British Gas PLC
Original Assignee
British Gas PLC
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 British Gas PLC filed Critical British Gas PLC
Priority to GB8711767A priority Critical patent/GB2204916B/en
Publication of GB8711767D0 publication Critical patent/GB8711767D0/en
Publication of GB2204916A publication Critical patent/GB2204916A/en
Application granted granted Critical
Publication of GB2204916B publication Critical patent/GB2204916B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1787—General system configurations
    • G10K11/17873—General system configurations using a reference signal without an error signal, e.g. pure feedforward
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17857—Geometric disposition, e.g. placement of microphones
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17861—Methods, e.g. algorithms; Devices using additional means for damping sound, e.g. using sound absorbing panels
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/10—Applications
    • G10K2210/107—Combustion, e.g. burner noise control of jet engines
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/10—Applications
    • G10K2210/121—Rotating machines, e.g. engines, turbines, motors; Periodic or quasi-periodic signals in general
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/321—Physical
    • G10K2210/3212—Actuator details, e.g. composition or microstructure
    • G10K2210/32121—Fluid amplifiers, e.g. modulated gas flow speaker using electrovalves
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/321—Physical
    • G10K2210/3214—Architectures, e.g. special constructional features or arrangements of features
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/50—Miscellaneous
    • G10K2210/509—Hybrid, i.e. combining different technologies, e.g. passive and active

Abstract

A silencer 1 for reducing noise from the intake or exhaust of machinery or equipment such as a gas stream "X" exiting a power turbine gas volute comprises a passive silencer part 2, with a single substantially unobstructed gas path, an active silencer part 3 adapted to reduce noise over a frequency range which is complementary to the passive silencer part, and a casing 4 which provides at least a support for the active silencer part 3. The casing 4 may be tubular and has supports 5 projecting away from the interior thereof, there being hollow enclosures 6 of the active silencer part 3, which enclosures are hollow, are rectangular or annular in transverse cross-section, and provide relatively large air-filled volumes between the supports 5 and loudspeaker cones 7 which extend obliquely to the longitudinal axis of the enclosures: 6. The passive silencer part 3 comprises a glass fibre lining 12 with metal partitions 14, outwardly of a perforated casing 13. Microphones 18 are located in the lining 12. <IMAGE>

Description

A SILENCER The invention relates to a silencer, particularly a silencer for reducing noise from the intake or exhaust of machinery or equipment such as a hot noisy, gas stream issuing from a power turbine exhaust.
It is often necessary for environmental and other reasons to seek to reduce or cancel the noise which is emitted from an intake or exhaust opening. It has been proposed to achieve such a result by using what are known as Active Noise Reduction (ANR) systems, which are "added on retrospectively to an existing silencer system.
Such ANR systems which have been proposed have various disadvantages, such as the fact that when installed as a single ring of noise reduction or cancelling sources, they are limited as the highest frequency at which they can usefully operate is approximately C/3D, where C is the velocity of sound and D is the diameter of the ring.
Another disadvantage of the proposed systems is the cost, as generally large amplification of the cancelling acoustic signals is required because of limitations imposed by the existing hardware. A further disadvantage of retrospective installation of an ANR system is that the inherent benefits of reduced silencer size, less materials, less structual support, and minimal pressure losses cannot be exploited fully.
Accordingly, it is an object of the invention to seek to mitigate these disadvantages.
According to one aspect of the invention there is provided a silencer for reducing noise in a gas stream, comprising a passive silencer part with an unobstructed path for the gas stream, an active silencer part adapted to reduce noise and a casing which provides at least a support for the active silencer part.
The outer casing will normally be tubular and may define enclosures, as considered in use, of the active silencer part, in particular the casing may form part of the enclsoures which contain the volumes behind the active sources.
The casing may include means projecting away from the interior thereof and which may support the enclosures.
The projecting means may comprise struts on which the enclosure may be supported at an end remote from an active source of the active silencer part. The struts may also support a platform or ladders providing access to the active silencing sources.
The active silencer part may comprise a plurality of loudspeaker cones or other active sources, for example pneumatic pressure generators.
The enclosures may be rectangular or annular in transverse cross-section and may be spaced from the outer boundary of the casing.
The interior of the casing may be lined with a sound absorbent lining, for example long strand glass fibre.
The lining may comprise means to attenuate the frequency of the noise of the gas stream in use.
The attenuation means may comprise a plurality of discrete partitions spaced apart along the length of lining and embedded therein.
Where the sound absorbent lining is thicker than 0.2 of the internal diameter of the silencer then additional useful noise reduction may be achieved by spacing adjacent solid partitions at a distance of 0.60 to 0.85 of the diameter of the active silencer part. In this case, additional partitions to reduce the settlement of sound absorbent lining may be included provided these partitions are perforated or otherwise made fairly transparent to sound The spacing of solid partitions may be at a distance of 0.75 of the diameter of the outer casing.
In addition to the spacing of the partitions and, as an alternative means of providing attenuation of noise in the frequency region corresponding to the useful upper limit of the ANR system, then the volume V of the filled space enclosed by the partitions, outer casing and internal perforated sheet and the acoustic conductivity Co of the perforated sheet may be chosen such that V/Co equals k/D2, where k depends primarily on the temperature distribution and is typically in the range 4 - 5 and D is the diameter of the array of active sources.
There may be louvres downstream of the active silencer part to minimise the effect of the weather or the environment.
The active silencer part may be at the outlet of the casing.
According to a second aspect of the invention, there is provided an exhaust system for a gas stream including a silencer as hereinbefore defined.
The exhaust system may include a power turbine exhaust volute.
A silencer for reducing noise in a hot gas stream is diagrammatically illustrated, by way of example, with reference to the accompanying drawing, which shows a longitudinal sectional view of the silencer.
Referring to the drawing, there is shown a silencer 1 for reducing noise in a gas stream X such as a stream leaving a power turbine gas volute (not shown), the silencer comprising a passive silencer part 2, an active silencer part 3 adapted to reduce noise in the gas stream, and a tubular casing 4 which provides at least a support for the active silencer part 3.
The casing 4 suitably has support means 5 projecting away from the interior thereof, there being upstream enclosures 6, as considered in use, of the active silencer part 3, or source, which enclosures provide relatively large air-filled volumes between the support 5 and loudspeaker cones 7 which in the embodiment shown extend obliquely to the longitudinal axis of the enclosure 6. The enclosure 6 is thus a hollow body defined by substantially parallel walls 8 and 9 the inner one 8 of which is spaced from the casing 4 to provide a space 10 through which cooling ambient air "Y" is entrained to flow longitudinally of the casing 4, exteriorly thereof to effect cooling The support 5 is an annular channel-shaped in cross-section metal member, bracket or strut which is secured to the casing 4 as by welding.Limbs 11 of the channel are spaced a sufficient distance apart just to accommodate the walls 8 and 9 of the enclosure 6, whereby to provide a positive support therefor.
The interior of the casing is lined with a densely packed sound absorbent lining 12, of long strand glass fibre for example. In order to provide attentuation of the noise of the gas stream "X" in use, the inner silencer casing 13 is perforated in the usual manner to allow the noise to be partially absorbed by the lining 12. There is additional attenuation means in the form of a plurality of discrete metal partitions 14 which are spaced apart along the length of the lining t2 and embedded therein to form discrete units of lining. The partitions 14 provide a reactive element, stated in another way an acoustic expansion means to provide attentuation at the frequency at which the active silencer part 3 becomes ineffective, and to achieve this, the lining has a length in the range 0.60 to 0.85, in the embodiment 0.75D, where D is the diameter of the active source outlets. In this embodiment the thickness of the absorbent lining has a minimum width of 0.2 of the internal diameter of the casing. The thickness of lining is chosen so that the volume V enclosed by the perforated inner sheet, outer casing and solid separation plates is a factor k multiplied by the acoustic conductivity of the perforated sheet and divided by the square of the diameter D of the active source outlets. For a uniform velocity of sound throughout the silencer, k is approximately 4.4.For gas turbine exhaust silencers the temperature distribution would be such that k might vary between 4 and 5.
The enclosure 3 extends beyond the loudspeaker cones and converges towards the exit from the silencer 1 and supports louvres 15 which allow emission of "anti-noise", while minimising the ingress of rain or hot gases.
In use, a convergent entry end 16 of the silencer, which may require a transition from rectangular to circular cross section, is mounted on say the exit of a power turbine exhaust volute. Hot noisy gas "X" entering therefrom passes through the interior of the silencer which acts as the passive silencer part which is totally unobstructed, and exits at the exit 17 of the silencer. The active silencer part detects the noise by detectors 18 eg. microphones or other pressure transducers some or all of which are positioned in the upper half of the passive silencer. These detectors are not in the gas stream itself but are protected from temperature and flow effects by location within the part of the passive silencer which is filled with densely packed absorptive material.The signals from the detectors are then processed so that the active sources emit cancelling noise which has similar magnitude, substantially opposite phase and similar spatial radiation properties to the noise emitted to the noise emitted from the exhause opening.
The net effect is that the noise is reduced at least at any observer location remote from the exhaust outlet.
The silencer 1 described and shown with reference to the drawing thus provides cancelling sources which do not result in static pressure drop, and so do not lead to inefficiency of the turbine and associated machinery. Moreover, the silencer is compact so making it relatively inexpensive to build and install, as the requirements for supporting steelwork or foundations are less. Further, as it is relatively short, it is less visable and thus acceptable environmentally. The passive silencer part can be provided with a minimum outlet diameter to give an optimum loudspeaker arrangement without increasing gas velocities above 45 - 55ms-1, which would cause turbulence leading to noise generation and higher pressure losses. The passive silencer part is totally unobstructed so high pressure drop and unpleasant aerodynamic effects are avoided.
It will be understood that the silencer can be modified. For example the casing 4 and enclosure 6 could be an integral one piece unit, if temperatures allow. Also the exit of the silencer could be connected with a chimney, so that in effect the active source 7 can be at any desired position which is substantially downstream of at least part of the absorptive lining.

Claims (18)

1. A silencer for reducing noise in a gas stream, comprising a passive silencer part with an unobstructed path for the gas stream, an active silencer part adapted to reduce noise, and a casing which provides at least a support for the active silencer part.
2. A silencer according to Claim 1, the casing being tubular and defining enclosures, as considered in use, of the active silencer part.
3. A silencer according to Claim 2, the casing including means projecting away from the interior thereof and supporting the enclosure.
4. A silencer according to Claim 3, the projecting means including a strut on which the enclosure is supported at the end remote from the active sources of the active silencer part.
5. A silencer according to Claim 4, the active silencer part comprising a plurality of loudspeaker cones or other active sources.
6. A silencer according to Claim 4 or Claim 5, the enclosures being rectangular or annular in transverse cross-section and spaced from the outer boundary of the casing.
7. A silencer according to Claim 6, the interior of the casing being lined with a sound absorbent lining.
8. A silencer according to Claim 7, the lining being formed into means to attentuate the noise of the gas stream in use at frequencies which complement the operation of the active silencer part.
9. A silencer according to Claim 8, the attenuation means comprising a plurality of discrete partitions spaced apart along the length of lining and embedded therein.
10. A silencer according to Claim 9, adjacent partitions being spaced by a distance 0.60 to 0.85 of the diameter of the active source outlets.
11. A silencer according to Claim 10, the distance being 0.75 of the casing.
12. A silencer according to claim 9, the volume or volumes filled with lining which are formed by the casing, discrete partitions and perforated inner sheet exposed to the gas stream having a fundamental natural frequency or frequencies within one third of one octave of the useful upper frequency limit of the active part of the silencer.
13. A silencer according to any preceding claim in which some or all of the microphones, pressure transducers or other detectors in the active part are embedded in the lining and are not in the gas stream itself.
14. A silencer according to any preceding claim, including louvres downstream of the active silencer,part.
15. A silencer according to any preceding claim, the active sources being at the outlet of the casing.
16. A silencer for reducing noise in a gas stream, substantially as hereinbefore described with reference to the accompanying drawing.
17. An intake or exhaust system for a gas stream, including a silencer according to any preceding claim.
18. An exhaust system according to Claim 17, a power turbine exhaust volute.
GB8711767A 1987-05-19 1987-05-19 A silencer Expired - Fee Related GB2204916B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8711767A GB2204916B (en) 1987-05-19 1987-05-19 A silencer

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8711767A GB2204916B (en) 1987-05-19 1987-05-19 A silencer

Publications (3)

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GB8711767D0 GB8711767D0 (en) 1987-06-24
GB2204916A true GB2204916A (en) 1988-11-23
GB2204916B GB2204916B (en) 1991-10-16

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Family Applications (1)

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0473095A2 (en) * 1990-08-30 1992-03-04 Fridolin Peter Prof. Dr. Mechel Hybrid sound attenuator
EP0491373A2 (en) * 1990-12-19 1992-06-24 Gold Star Co. Ltd Method of, and device for reducing noises generated at an indoor unit of a separate type room air conditioner package
EP0542749A1 (en) * 1990-04-09 1993-05-26 Noise Cancellation Technologies, Inc. Noise cancellation apparatus
EP0615648A1 (en) * 1991-12-02 1994-09-21 Noise Cancellation Technologies, Inc. Active noise control of an enclosure with multiple transducers
EP0642115A3 (en) * 1993-08-06 1995-05-17 Shinko Electric Co Ltd Vibratory parts-feeder apparatus.
EP0667757A1 (en) * 1992-10-13 1995-08-23 WAGENFELD, Robert Active gas turbine (jet) engine noise suppression
DE102012006329A1 (en) 2011-04-01 2012-10-04 Alstrom Technology Ltd. Gas turbine and intake manifold

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3685611A (en) * 1971-03-24 1972-08-22 Rohr Corp Duct with lining of spaced bands for suppressing sound in a gas steam transmitted therethrough
GB1357330A (en) * 1970-07-01 1974-06-19 Secr Defence Dynamic silencing systems
GB1456018A (en) * 1972-11-24 1976-11-17 Nat Res Dev Active control of sound waves
GB2142091A (en) * 1983-06-23 1985-01-09 Nat Res Dev Attenuation of sound waves

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1357330A (en) * 1970-07-01 1974-06-19 Secr Defence Dynamic silencing systems
US3685611A (en) * 1971-03-24 1972-08-22 Rohr Corp Duct with lining of spaced bands for suppressing sound in a gas steam transmitted therethrough
GB1456018A (en) * 1972-11-24 1976-11-17 Nat Res Dev Active control of sound waves
GB2142091A (en) * 1983-06-23 1985-01-09 Nat Res Dev Attenuation of sound waves

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0542749A1 (en) * 1990-04-09 1993-05-26 Noise Cancellation Technologies, Inc. Noise cancellation apparatus
EP0542749A4 (en) * 1990-04-09 1994-05-25 Active Noise & Vibration Tech Single cavity automobile muffler
EP0473095A2 (en) * 1990-08-30 1992-03-04 Fridolin Peter Prof. Dr. Mechel Hybrid sound attenuator
EP0473095A3 (en) * 1990-08-30 1993-02-24 Fridolin Peter Prof. Dr. Mechel Hybrid sound attenuator
EP0491373A2 (en) * 1990-12-19 1992-06-24 Gold Star Co. Ltd Method of, and device for reducing noises generated at an indoor unit of a separate type room air conditioner package
EP0491373A3 (en) * 1990-12-19 1993-03-31 Gold Star Co. Ltd Method of, and device for reducing noises generated at an indoor unit of a separate type room air conditioner package
EP0615648A1 (en) * 1991-12-02 1994-09-21 Noise Cancellation Technologies, Inc. Active noise control of an enclosure with multiple transducers
EP0615648A4 (en) * 1991-12-02 1995-04-19 Noise Cancellation Tech Active noise control of an enclosure with multiple transducers.
EP0667757A1 (en) * 1992-10-13 1995-08-23 WAGENFELD, Robert Active gas turbine (jet) engine noise suppression
EP0667757A4 (en) * 1992-10-13 1996-10-16 Robert Wagenfeld Active gas turbine (jet) engine noise suppression.
EP0642115A3 (en) * 1993-08-06 1995-05-17 Shinko Electric Co Ltd Vibratory parts-feeder apparatus.
DE102012006329A1 (en) 2011-04-01 2012-10-04 Alstrom Technology Ltd. Gas turbine and intake manifold
US9181875B2 (en) 2011-04-01 2015-11-10 Alstom Technology Ltd Gas turbine air intake manifold controllably changing a mechnical rigidity of the walls of said intake manifold

Also Published As

Publication number Publication date
GB2204916B (en) 1991-10-16
GB8711767D0 (en) 1987-06-24

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PCNP Patent ceased through non-payment of renewal fee

Effective date: 19990519