WO1998012420A1

WO1998012420A1 - Rotating machinery active noise control

Info

Publication number: WO1998012420A1
Application number: PCT/US1997/016500
Authority: WO
Inventors: Daryl N. May; Robert L. Chapkis
Original assignee: Mcdonnell Douglas Corporation
Priority date: 1996-09-23
Filing date: 1997-09-18
Publication date: 1998-03-26
Also published as: AU4421497A

Abstract

The present invention provides a system for reducing noise caused by a rotating component (46) generating a source signal by use of a plurality of cancelling signal emitters (72, 94, 100) rotating in phase with the rotating component. The emitters (72, 94, 100) are adapted to emit fluid under pressure along a path of said source signal such that an inverted pressure wave is created relative to the pressure wave of the source signal. Preferably, the system includes at least one duct (95) operably coupled to the plurality of cancelling signal emitters (72, 94, 100) for directing the fluid under pressure from a high pressure area to the plurality of cancelling signal emitters (72, 94, 100). According to the invention, a predetermined number of obstructions (74) are circumferentially disposed about the rotating component. The obstructions (74) rotate in concert with the rotating component (46) so that fluid under pressure is emitted from a plurality of openings (72).

Description

TITLE: ROTATING MACHINERY ACTIVE NOISE CONTROL

BACKGROUND OF THE INVENTION

1. Technical Field

This invention generally relates to noise control and more particularly, to reducing noise generated from rotating machinery, such as aircraft engine blades including fans, rotors, and propellers, using active noise control .

2. Discussion

As is generally known in the acoustical art, reducing noise from rotating machinery, such as aircraft engine blades including fans, rotors, and propellers, is difficult to achieve because the noise sources and propulsive forces are co- located. Therefore, the reduction of noise cannot be easily accomplished without also reducing propulsive forces. Moreover, the propagation of noise from aircraft engines from the source to the receiver, such as a person on the ground or in the airplane, is not easily interrupted by walls, enclosures, or other forms of barrier.

In the case of aircraft engine blades, the principal methods of conventionally reducing noise are to design for an appropriate number of blades, aerodynamic loadings and speeds, to maintain adequate distances between blades and other components, and, if possible, to use sound absorptive treatments on the surfaces of ducts through which air enters and exits the various blades. These noise control features frequently penalize rotating machinery design from other standpoints, such as by raising weight and aerodynamic drag, and introducing complexity. Thus, it is desirable to provide a system for reducing noise from rotating machinery at or near the source without having to design against noise in the conventional ways.

One known system for reducing noise at or near the source is known as "active noise control" . One form of this control is to introduce noise signals, the "canceling signals", with a phase opposite to those from the source, "source signals", at relevant receiver locations. However, there are difficulties in doing this, including the challenge of achieving a strong noise canceling signal, the difficulty of locating the source of the signal in such a way that the reversal of phase is, achieved at an appropriately extensive number of receiver points, and the need to achieve reliability in the noise canceling signal system so that the conventional noise control devices can be eliminated or reduced in their extent .

Prior to the present invention, these challenges have not been effectively surmounted in the case of rotating machinery noise sources, and especially not in the case of aircraft engines. Loudspeaker and similar electromagnetic driven mechanical sources have been used in an attempt to reduce fan noise in ducts. However, these have been low acoustic power fans as compared with aircraft engine acoustic power outputs. Furthermore, the duct has been an intrinsic part of the overall system, which cannot therefore be eliminated. Loudspeaker devices have also been used in an attempt to reduce aircraft propeller noise, but applications have been extremely limited, and success has been modest in terms of noise reduction achieved.

Therefore, it is desirable to provide an active noise control system capable of achieving a strong noise canceling signal that is reliable enough to afford dispensing with conventional noise control devices.

SUMMARY OF THE INVENTION

The above and other objects are provided by a noise control system comprising a plurality of canceling signal emitters rotating in phase with the rotating component source signals. The emitters are adapted to emit fluid under pressure along a path of said source signal such that an inverted pressure wave is created relative to the pressure wave of the source signal. Preferably, the system includes at least one duct operably coupled to the plurality of cancelling signal emitters for directing the fluid under pressure from a high pressure area to the plurality of cancelling signal emitters. According to the invention, a predetermined number of obstructions are circumferentially disposed about the rotating component. The obstructions rotate in concert with the rotating component so that fluid under pressure is emitted from a plurality of openings.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to appreciate the manner in which the advantages and objects of the invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings only depict preferred embodiments of the present invention and are not therefore to be considered limiting in scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIG. 1 is a perspective view of an aircraft having rotary type turbine engines suspended from the wings thereof ;

FIG. 2 is a partially cut-away perspective view of a rotary type turbine engine having an active noise reduction system incorporated therein according to the present invention;

FIG. 3 is a schematic view of a first fan duct embodiment of the present invention;

FIG. 4 is a schematic view of a second and third fan duct embodiment of the present invention; FIG. 5 is a schematic view of a shaft embodiment of the present invention; and

FIG. 6 is a schematic view of an on blade embodiment according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The system described herein is advantageous over other known devices for creating a canceling noise signal to reduce the noise from rotating machinery. For instance, high levels of canceling noise signal are possible, the power source for the canceling noise signal is generated close to the source signal, and can be drawn from existing bleed systems. Also, the frequency of the canceling noise signal is locked to the frequency of the source signal, i.e., there is generally a mechanical connection between them, which is more reliable than electronic systems. Moreover, any desired phase difference between the signals is also generally achieved through reliable mechanical connections. Referring to FIG. 1, an airplane incorporating an active noise control system according to the present invention is shown generally at 10. As is generally known, the aircraft includes a body 12, a port wing 14 extending laterally from a port side 16 of the body 12 and a starboard wing.18 extending laterally from a starboard side 20 of the body 12. An elevator 22 is horizontally disposed at an aft end 24 of the body 12 and a rudder 26 is vertically disposed thereover. Furthermore, a cockpit 28 is formed within a fore end 30 of the body 12 and a passenger compartment 32 and a cargo hold 34 are located within the interior of the body 12. Windows 36 are provided within the body 12- to permit viewing from the passenger compartment 32 to the exterior of the body 12.

A plurality of aircraft jet engines 38 are suspended below the port and starboard wings 14, 18 by pylons 40 extending therebetween. For the purposes of this disclosure the engine 38 is herein defined to also include the nacelles. The plurality of aircraft jet engines 38 are a source of substantial noise when operated. The noise can be so loud that it affects or annoys the passengers within the passenger compartment 32, the flight crew within the cockpit 28, the ground crew 42 on the ground in the vicinity of the aircraft 10, and other observers 44 in reasonable proximity to the aircraft 10, including those on the ground when the aircraft is in flight. The present invention, which is implemented within the engines 38, serves to reduce the noise from the rotating machinery within the engines 38.

Turning now to FIG. 2, one aircraft jet engine 38 of FIG. 1 is shown in greater detail. As is known, the type of engine 38 generally utilized for propelling large airliners is a turbo fan engine. At the front of the engine 38, a fan 46 is rotatably mounted on a shaft 48 and operates to draw air into the engine 38. A compressor 50 is located rearward of the fan 46 and is disposed along a second shaft which is concentric to the shaft 48. The compressor 50 contains multiple sets of rotating blades 54 interspersed with stationary stators 52 which, in combination, act on a portion of the air from the fan 46 which enters therein. The compressor 50 operates to raise the pressure of the air, which then flows to the combustors or combustion chambers 56 disposed rearward of the compressor. Within the combustors 56, flames of burning fuel (not shown) heat the air, which expands. The hot, high-pressure air is directed rearward such that it rushes toward the exhaust nozzle 58. However, the air first passes through turbines 61 which are operably coupled to drive the compressor 50 and the fan 46.

Any air drawn in by the fan 46 which does not pass through the compressor 50, combustors 56, and turbines 61, passes along the interior of an air duct 60. This air moves more slowly than the air passing through the compressor, and when mixed with the faster-moving compressor air when emitted from the turbine, reduces the speed of the compressor air and results in reduced jet noise . The jet engine fan duct is shown at 60 and is defined herein as the approximately cylindrical structure 62 which immediately surrounds the engine fan blades 64 and forms the boundary 66 to the air duct through which the fan air passes. In the case of turbojet engines, which have no fan duct, the equivalent duct for purposes of this disclosure is actually the inlet to the compressor. Moreover, for both turbojet and turbofan engines, the discussion herein regarding the fan duct and the fan shall be taken to be also applicable to the turbine duct and the turbines.

Bleed air is drawn from the engine 38 and ducted to an annulus or annuli 68. One wall of the annulus 68 is formed by the inner wall 70 of the air duct 66, i.e., the wall in closest proximity to the fan blades 64. A slit 72 is formed in the annulus 68 around its entire circumference, which creates an opening between the annulus 68 and the air duct 60. A predetermined number of solid objects 74 are disposed in the immediate proximity of the slit 72 which physically block the air outflow. Thus, bleed air entering the annulus 68 is free to exit into the air duct 60 except for the presence of the solid objects 74 which serve as rotating obstructions to that emission. The solid objects 74 are spaced circumferentially, and rotate, such that the air emitted from the slit 72 does so in a radial direction which varies with time. The strength of the air pulses is controlled by the air pressure bled to the annulus 68. Also, the position of the openings 76 between the solid objects 74 maintains a constant relationship with the position of the rotating fan blades 64. The strength and position of the air emission from the slit 72 are the governing variables for the canceling noise signal. The strength of the air emission (i.e., pressure) may be self-regulating by virtue of the changing pressure of the available air bleed with engine power settings. It should be noted that bleed air may be used as an air cushion between the fixed air duct 60 and the rotating solid objects 74 for the purposes of reducing friction and maintaining clearances.

The position of the air emission points relative to the rotating fan blades is preferably fixed for practical reasons. Yet, because it may be desirable in some situations to change the position of the air emission point, such as when the local speed of sound changes, it is expected that some variable geometry may be incorporated into the present invention. It should be noted that the holes/openings 76 and solid objects 74 may require application based shaping to create a pressure variation with circumferential position that is of the appropriate form. Generally, a sound wave is emitted from the surface 80 of each blade 82 of the fan 46, compressors 50, and turbines 61. Certain portions of the blade surface 80 carry more loading than others and therefore emit more noise. Normally, such high emission portions are located toward the blade tip 84 where the rotational speeds are higher.

Such sound waves normally exit from the aircraft engine 38 in one of two ways. First, a plane wave may propagate from the blade tip 84 and move axially along the air duct 60 to an exit 86. Such exits exist at both ends of the duct 60. Alternatively, the sound wave may propagate from the blade tip 84 and follow a helical path. The sound wave diverges from an axial axis and circumferentially travels about the air duct 60. As such, the sound wave "spirals" its way to an exit 86.

The present invention makes use of fluid under pressure, which is caused to emit from locations which rotate in phase with and therefore at the same rotational speed as the rotating machinery noise sources. In the most general sense, fluid is bled from a high pressure area within the engine 38 and is ducted to various emission points along the path of the emitted wave. The fluid emission under pressure is caused to occur at locations relative to the sound source signals that will produce an inverted pressure wave which causes phase reversal at sound receiving points. It should be noted that such fluid emissions created by the fluid under pressure comprise the same fluid type as that which passes through the turbomachinery. Therefore, these emissions of fluid under pressure are preferably gaseous, in the case of gas turbine machinery

"turbomachinery", and are preferably liquidic, in the case of liquid turbomachinery. The fluid is transported from a high fluid pressure location through ducts, pipes, and the like before being emitted in the manner described elsewhere in this description. In this description, emphasis is given to aircraft jet engine noise reduction, but obvious read-across exists to other forms of rotating machinery.

Referring now to FIG. 3, the solid objects 74 can be constructed in a number of different ways or forms. Preferably, the solid objects 74 are included as part of the fan blade 82 or a fan blade row 88. Thus, in the first Fan Duct embodiment shown in FIG. 3, the existing fan blade tips 84 have extensions 90 disposed thereon in a circumferential direction and/or in a fore-and-aft direction. That is, the extensions 90 project from the fan blade tips 84 in a direction at an angle to the plane of the fan blade row 88. Preferably, the extensions are located in close proximity to or partially within the slit 72. In this way, the extensions 90 comprise the solid objects 74 referred to above.

In a second Fan Duct embodiment shown in FIG. 4, all the fan blades 82 in a blade row 88 are either mechanically attached to or push-against-to-rotate a common, ring-shaped end-plate 92. The end-plate 92 is disposed circumferentially about the blade tips 84 and is the solid object 74 referred to above. The end-plate 92 has holes/openings 94 formed therethrough to create the rotating air emission points previously described.

In a third Fan Duct embodiment also shown in FIG. 4, the blade row end-plate 92 having holes/openings 94 formed therein for permitting air flow from the annulus 68 is disposed circumferentially about the fan tips 84. However, in this embodiment, the end-plate 92 functions as an annular ring which is caused to rotate by electromagnetic or other means. Therefore, the end-plate 92 is not mechanically connected to the fan blades 82 at all. The third Fan Duct embodiment is an exception to the statement above that mechanical connections are generally used.

A fourth embodiment of the present invention is shown in FIG. 5 and is referred to as the Shaft version. In this embodiment, the previously-mentioned bleed air is directed by a duct 95 to a plenum or plenums 96 formed within the aircraft engine shaft or shafts 48. It should be noted that the shaft 48 is defined herein to include any hub or spinner 98. A plurality of holes/openings 100 are formed circumferentially about the shaft 48. Bleed air is emitted in an approximately radial direction from the circumferential holes/openings 100 between the plenum 96 and the engine's main air duct 60. The holes/openings 100 rotate with the shaft 48 at the same rotational speed as the blade row 102. It should be noted that the blade row 102 can be a fan blade row 88, a compressor blade row 104, or a turbine blade row 106. The holes/openings 100 are located circumferentially and/or in a fore-and-aft direction in the positions most effective for producing phase reversal of the source signal from the rotating blades 82. Thus, a canceling signal is derived from the holes/openings 100.

A fifth embodiment of the present invention is shown in FIG. 6 and is generally referred to as an On-Blade version. In this embodiment, bleed air from the engine 38 is directed through ducts 106 disposed within individual blades 82 of the fan 46, compressor 50, or turbine 61. The bleed air is then emitted through holes/openings 108 located on the blades 82 or on extensions 110 of the blades 82. The holes 108 are located on the blades 82 in the positions most effective for producing the phase reversal described above. This embodiment locates the sound canceling signal very close to the sound source signal, which is of great benefit.

Thus, the present invention creates cancelling noise signals to reduce the noise from rotating machinery. To accomplish this, fluid under pressure is emitted from locations rotating in phase with rotating machinery noise sources. The fluid emissions which produce this "cancelling signal" create a pressure wave having a phase relative to the pressure wave from the machinery noise signals (the "source signals") such that the overall sound pressure wave from the engine is reduced or eliminated along the sound propagation path from the engine to the sound receiving points by the interaction of the two waves.

The present invention is particularly useful in conjunction with turbine engines of all categories, including the rotating components they may drive, e.g., propellers on aircraft and submarines, load turbines, and helicopter main and tail rotors. Also, the present invention works well with other types of rotating machinery in which significant sound power is generated by rotating parts. These particularly include HVAC fans.

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and following claims.

Claims

CLAIMSWhat is Claimed is:

1. A noise control system comprising: a plurality of noise-cancelling signal emitters rotating in phase with signal sources in rotating machinery; and said plurality of cancelling signal emitters emitting fluid under pressure.

2. The system of claim 1 wherein said plurality of cancelling signal emitters emit said fluid under pressure along a path of said source signal to create an inverted pressure wave.

3. The system of claim 1 further comprising at least one duct operably coupled to said plurality of cancelling signal emitters for directing said fluid under pressure from a high pressure area to said plurality of cancelling signal emitters.

4. A noise control system comprising: an engine; at least one annulus disposed circumferentially about said rotating component; said at least one annulus having a slit formed therein; a predetermined number of obstructions circumferentially disposed adjacent said slit defining a plurality of openings therein; and said obstructions rotating in concert with a rotating component such that fluid under pressure is emitted from said plurality of openings.

5. The system of claim 4 wherein said plurality of openings emit said fluid under pressure along a path of said source signal to create an inverted pressure wave .

6. The system of claim 4 further comprising at least one duct operably coupled to said plurality of openings for directing said fluid under pressure from a high pressure area to said plurality of openings.

7. The system of claim 4 wherein said plurality of obstructions further comprise a plurality of extensions coupled to said rotating component.

8. The system of claim 4 wherein said plurality of openings further comprise a plurality of holes formed in a ring shaped end-plate coupled to said rotating component.

9. The system of claim 4 wherein said rotating component further comprises one of a fan blade row, a compressor blade row, and a turbine blade row.

10. A noise control system comprising: an engine; a plurality of extensions coupled to a plurality of blades at an angle to the plane thereof; at least one annulus disposed circumferentially about said plurality of blades; said at least one annulus having a slit formed therein; said plurality of extensions circumferentially disposed adjacent said slit defining a plurality of openings therein; and said plurality of extensions rotating in concert with said plurality of blades such that fluid under pressure is emitted from said plurality of openings.

11. The system of claim 10 wherein said plurality of openings emit said fluid under pressure along a path of said source signal to create an inverted pressure wave.

12. The system of claim 10 further comprising at least one duct operably coupled to said plurality of openings for directing said fluid under pressure from a high pressure area to said plurality of openings.

13. The system of claim 10 wherein said plurality of blades further comprises one of a fan blade row, a compressor blade row and a turbine blade row.

14. A noise control system comprising: an engine; a ring-shaped end-plate disposed circumferentially about a plurality of blades; said end-plate having a plurality of openings formed therethrough; said end-plate rotating in concert with said plurality of blades such that fluid under pressure is emitted from said plurality of openings.

15. The system of claim 14 wherein said plurality of openings emit said fluid under pressure along a path of said source signal to create an inverted pressure wave.

16. The system of claim 14 further comprising at least one duct operably coupled to said plurality of openings for directing said fluid under pressure from a high pressure area to said plurality of openings.

17. The system of claim 14 wherein said ring-shaped end-plate is mechanically secured to said plurality of blades .

18. The system of claim 14 wherein said ring-shaped end-plate is electromagnetically secured to said plurality of blades .

19. The system of claim 14 wherein said plurality of blades further comprises one of a fan blade row, a compressor blade row, and a turbine blade row.

20. A noise control system comprising: an engine; a rotatable shaft disposed within said engine; said shaft including a plenum formed therein; a plurality of openings formed circumferentially about said shaft adjacent a plurality of blades such that fluid under pressure is emitted from said plenum through said plurality of openings.

21. The system of claim 20 wherein said plurality of openings emit said fluid under pressure along a path of said source signal to create an inverted pressure wave.

22. The system of claim 20 further comprising at least one duct operably coupled to said plenum for directing said fluid under pressure from a high pressure area to said plurality of openings.

23. The system of claim 20 wherein said shaft further comprises a hub disposed thereon.

24. The system of claim 20 wherein said plurality of blades further comprises one of a fan blade row, a compressor blade row, and a turbine blade row.

25. A noise control system comprising: an engine ; a plurality of blades including at least one opening formed therein; at least one duct disposed within said plurality of blades extending to said at least one opening; said at least one opening rotating in concert with said plurality of blades such that fluid under pressure is emitted from said plurality of openings.

26. The system of claim 25 wherein said plurality of openings emit said fluid under pressure along a path of said source signal to create an inverted pressure wave.

27. The system of claim 25 wherein said at least one duct directs said fluid under pressure from a high pressure area to said plurality of openings.

28. The system of claim 25 wherein said plurality of blades further comprises one of a fan blade row, a compressor blade row, and a turbine blade row.

29. The system of claim 25 wherein said at least one opening is formed in at least one extension coupled to said plurality of blades.