Abstract:
A system for controlling a position of jet engine exhaust mixing tabs includes a plurality of exhaust mixing tabs spaced apart from one another and extending from a lip of an exhaust nozzle of a jet engine nacelle adjacent a flow path of an exhaust flow emitted from the exhaust nozzle. Each of the exhaust mixing tabs are constructed to be controllably deformable from a first position adjacent the flow path to a second position extending into the flow path of the exhaust flow in response to a control signal applied to each of the exhaust mixing tabs. In the first position, the exhaust mixing tabs either have no affect on the thrust produced, or increase the momentum (thrust) of the exhaust flow exiting from the exhaust nozzle. In the second position, that is, the “deployed” position, the exhaust mixing tabs are deformed to extend into the flow path. In this position the exhaust mixing tabs promote mixing of the exhaust flow with an adjacent air flow. This results in the attenuation of noise generated by the jet engine.

Description:
FIELD OF INVENTION 
   This invention relates to the reduction of noise produced by jet engines, and more particularly to an engine nacelle exhaust nozzle having an Irregular edge that forms a plurality of exhaust mixing tabs adapted to improve mixing of exhausts to attenuate noise produced by the engine. 
   BACKGROUND OF THE INVENTION 
   With present day jet aircraft, structures typically known in the industry as “chevrons” have been researched to attenuate noise generated by a jet engine. The chevrons have traditionally been fixed (i.e., immovable), triangular, tab-like elements disposed along a trailing edge of a primary and/or a secondary exhaust nozzle of the jet engine nacelle such that they project into the exhaust gas flow stream exiting from the exhaust nozzle. The chevrons have proven to be effective in reducing the broadband noise generated by the mixing of primary-secondary and secondary/ambient exhaust streams for high thrust operating conditions. Since the chevrons interact directly with the exhaust flow, however, they also generate drag and loss of thrust. Consequently, there is a tradeoff between the need to attenuate noise while still minimizing the loss of thrust due to the presence of the chevrons, 
   Noise reduction is typically needed for takeoff of an aircraft but not during cruise. Thus, any noise reduction system/device that reduces noise at takeoff (i.e., a high thrust condition) ideally should not significantly degrade the fuel burn during cruise. A compromise therefore exists between the design of static (i.e. immovable) chevrons for noise abatement and the need for fuel efficient operation during cruise. 
   Thus, there exists a need for a noise reduction system which provides the needed noise attenuation at takeoff but does not produce drag and a loss of thrust during cruise conditions. More specifically, there is a need for a noise reduction system which permits a plurality of chevrons to be used in connection with an exhaust nozzle of a jet engine to attenuate noise during takeoff, but which also permits the chevrons to be moved out of the exhaust gas flow path of the engine during cruise conditions to prevent drag and a consequent loss of thrust during cruise conditions. 
   BRIEF SUMMARY OF THE INVENTION 
   The above limitations are overcome by a noise reduction system in accordance with preferred embodiments of the present invention. In one preferred form the noise reduction system comprises a plurality of exhaust mixing tabs spaced apart from one another and extending from a lip of an exhaust nozzle of a jet engine nacelle adjacent a flow path of an exhaust flow emitted from the exhaust nozzle. Each of the exhaust mixing tabs are constructed to be controllably deformable from a first position adjacent the flow path to a second position extending into the flow path of the exhaust flow in response to a stimulus applied to each of the exhaust mixing tabs. In the first position, the exhaust mixing tabs either have no affect on the thrust produced, or increase the momentum (thrust) of the exhaust flow exiting from the exhaust nozzle. In the second position, that is, the “deployed” position, the exhaust mixing tabs are deformed to extend into the flow path. In this position the exhaust mixing tabs promote mixing of the exhaust flow with an adjacent air flow. This results in the attenuation of noise generated by the jet engine. 
   In one preferred embodiment each exhaust mixing tab has a plurality of sleeves attached to an inner surface of the respective exhaust mixing tab. A shape memory alloy (SMA) tendon is disposed within each of the sleeves. Each SMA tendon is attached at a first end to a forward edge of the respective exhaust mixing tab and attached at a second end along an aft portion of the respective exhaust mixing tab, offset from an aft edge of the respective exhaust missing tab. The SMA tendons are adapted to constrict when activated by heat. The constriction applies a linear pulling force on the aft portion to cause the exhaust mixing tabs to be deployed into an exhaust flow emitted from the nozzle. This causes intermixing of the exhaust flow with adjacent air flow, thereby attenuating noise generated as the exhaust flow exits the nozzle. An outer layer of each exhaust mixing tabs acts a biasing component to return the exhaust mixing tabs to a non-deployed position when the SMA tendons are deactivated. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. Furthermore, the features, functions, and advantages of the present invention can be achieved independently in various embodiments of the present inventions or may be combined in yet other embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and accompanying drawings, wherein; 
       FIG. 1  is a simplified side view of a nacelle for housing a jet engine of an aircraft, with the nacelle incorporating a plurality of exhaust mixing tabs of the present invention along a trailing circumferential lip portion of the secondary exhaust nozzle of the nacelle; 
       FIG. 2  is a partial side view of one of the exhaust mixing tabs taken in accordance with section line  2 — 2  in  FIG. 1 ; 
       FIG. 3A  is an illustration of a inner side of an exhausting mixing tab shown in  FIGS. 1 and 2 , having a plurality of shape memory alloy tendons attached, in accordance with a preferred embodiment of the present invention; 
       FIG. 3B  is a cross-sectional view of a shape memory alloy tendon encased in a sleeve shown in  FIG. 2 ; 
       FIG. 3C  is an illustration of the inner side of an exhausting mixing tab shown in  FIGS. 1 and 2 , having the shape memory allow tendons attached, in accordance with another preferred embodiment of the present invention; and 
       FIG. 4  is a simplified side view of the nacelle shown in  FIG. 1  in accordance with another preferred embodiment of the present invention. 
   

   Corresponding reference numerals indicate corresponding parts throughout the several views of drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application or uses. Additionally, the advantages provided by the preferred embodiments, as described below, are exemplary in nature and not all preferred embodiments provide the same advantages or the same degree of advantages. 
   Referring to  FIG. 1 , there is shown an engine nacelle  10  for housing a jet engine  14 . The nacelle  10  includes a primary exhaust gas flow nozzle  18 , also referred to in the art as a core exhaust nozzle that channels the exhaust flow of from a turbine (not shown) of the engine  14  out the aft end of the nacelle  10 . The nacelle  10  additionally includes a secondary exhaust gas flow nozzle  22 , also referred to in the art as a bypass fan exhaust nozzle, that directs the exhaust flow from an engine bypass fan (not shown) out of the aft end of the nacelle  10 . A plug  24  is disposed within the nacelle  10 . In a preferred embodiment, the secondary exhaust flow nozzle  22  includes a plurality of exhaust mixing tabs  26 . The exhaust mixing tabs  26  extend from a lip area  30  of the secondary flow nozzle  22 . As will be described in greater detail in the following paragraphs, in operation each of the exhaust mixing tabs  26  is deformed (i.e., bent or deflected) in response to a stimulus that causes shape memory allow (SMA) tendons  34  (shown in  FIGS. 2 ,  3  and  4 ) attached to the exhaust mixing tabs  26  to be heated. When heated the SMA tendon  34  constrict in a one-dimensional linear direction, thereby causing the exhaust mixing tabs  26  to extend (i.e., “be deployed”) partially into the exhaust gas flow path exiting from the secondary exhaust gas flow nozzle  22 . This is indicated by dashed lines  38  near the uppermost and lowermost exhaust mixing tabs  26  in the drawing of  FIG. 1 . The exhaust mixing tabs  26  are preferably arranged circumferentially around the entire lip portion  30  of the secondary exhaust gas flow nozzle  22 . 
   Referring to  FIG. 2 , a portion of one of the exhaust mixing tabs  26  is illustrated. It will be appreciated that in the industry the exhaust mixing tabs  26  are often referred to as “chevrons”. However, it should be appreciated that while the term “chevron” implies a triangular shape, the exhaust mixing tabs  26  are not limited to a triangular configuration, but may comprise other shapes such as, but not limited to, rectangles, trapezoids or portions of circles. The exhaust mixing tabs  26  each include a distal portion  42 , a root portion  46  and a nozzle extension portion  50 . The distal portion  42  is the principal portion that projects into the exhaust gas flow path discharged from the secondary exhaust gas flow nozzle  22 . The root portion  46  forms an intermediate area for transitioning from the distal portion  42  to the nozzle extension portion  50 . In a preferred embodiment, the nozzle extension portions  50  of the exhaust mixing tabs  26  are integrally formed with the lip portion  30  of the nacelle  10 . Alternatively, the nozzle extension portion  50  is secured the exhaust mixing tab  16  to the lip portion  30  of the secondary exhaust flow nozzle  22  using any suitable fastening means. For example, the nozzle extension portions  50  of the exhaust mixing tabs  26  can be secured to the lip  30  of the nacelle  10  with rivets, by welding, or any other suitable securing means. 
   Referring now to  FIGS. 2 ,  3 A,  3 B and  3 C the exhaust mixing tab  16  includes an outer layer  54  (best shown in  FIG. 2 ) constructed of any material suitable for the construction of jet engine nacelles. In a preferred embodiment, the outer layer  54  is integrally formed with the nacelle lip  30 . As best shown in  FIG. 3B , each SMA tendon  34  is enclosed in a sleeve  58  having an inner diameter that is slightly larger than an outer diameter of the SMA tendons  34  such that an air gap  60  exists between the SMA tendon and the sleeve  58 . The air gaps  60  allow the diameter of SMA tendons  34  to expand when the lengths of SMA tendons  34  shorten during activation without interference, as described further below. For clarity and convenience, only the SMA tendons  34  are shown in  FIGS. 3A and 3C , the sleeves  58  are not shown. Thus, although the sleeves  58  are not shown, it should be understood that each SMA tendon  34  shown in  FIGS. 3A and 3C  are enclosed within a related sleeve  58 . The sleeves  58  are attached to and conform with the contour of the an inner side  64  of the exhaust mixing tabs  26 . The sleeves  58  retain the SMA tendons  34  in effectively the same contour when the SMA tendons  34  are activated to generate a pulling force that bends the respective exhaust mixing tabs  26  into the exhaust flow. 
   A first end  62  (best shown in  FIGS. 3A and 3C ) of each SMA tendon  34  is attached to the inner side  64  of the related exhausting mixing tab  26  at a forward edge  66  that is adjacent the nacelle lip  30 . An opposing second end  68  of each SMA tendon  34  is attached to the inner side  64  of exhaust mixing tab  26  along an aft edge  70 , i.e. the trailing edge. In a preferred form, the second ends  68  are offset from the aft edge  70  to generate a greater end moment and resultant inward deflection, when the SMA tendons  34  are activated. That is, the second ends  68  are attached to the inner side  70  a short distance from the aft edge  70 , as shown in  FIG. 2 . The first and second ends  62  and  68  of the SMA tendons  34  are attached to the exhaust mixing tabs  26  using any suitable means, such as termination by swaged ferrule or clamping into an end block. 
   Each sleeve is affixed, bonded or otherwise suitably secured to the inner side  64  of the related exhaust mixing tab  26  using any suitable means, such as adhesive bonding or embedding in a compliant filler material. In a preferred embodiment, the length of each sleeve  58  is shorter than the length of the SMA tendon  34  enclosed therein. Therefore, at least one end of each SMA tendon  34  extends past the end of the respective sleeve  58 . This allows the SMA tendon  34  to constrict, i.e. shorten in length, when activated. The SMA tendons  34  are activate by heating the SMA tendons  34 . For example, the SMA tendons  34  can be heated by the ambient air temperature exhaust gas flow emitted from the secondary exhaust gas flow nozzle  22  or by a separately controlled heat source. 
   When the SMA tendons  34  constrict, i.e. in an austenitic state) force is applied to the inner sides  64  of the respective exhaust mixing tabs  26 . This force causes the exhaust mixing tabs  26  to deploy, i.e. curve or curl inward, into the bypass fan exhaust flow, thereby causing an improved mixing of the exhaust with the ambient air. Therefore, noise generated by the engine  14  is attenuated. In one preferred form the SMA tendons  34  comprise wires constructed of a nickel-titanium alloy. More preferably, nickel-titanium shape-memory alloy is used for the SMA tendons  34 . The geometry or pattern in which the SMA tendons are attached to the inner sides  64  of the exhaust mixing tabs  26  is dependent on the desired shape of the exhaust mixing tabs  26  when deployed. That is, it may be desirable to deploy the exhaust mixing tabs  26  such that each exhaust mixing tab  26  curls inward in a linear roll fashion, whereby the exhaust mixing tabs  24  have a non-cupped curvature. Or, it may be desirable to deploy the exhaust mixing tabs  26  such that each exhaust mixing tab  26  curves inward to take on a concave or cupped form. 
   For example, as shown in  FIG. 3A , the SMA tendons can be disposed on the inner side  64  of each exhaust mixing tab  26  in essentially a ‘parallel line’ pattern. Alternatively, as shown in  FIG. 3C , the SMA tendons can be disposed on the inner side  64  of each exhaust mixing tab  26  in a ‘fan-like’ pattern. Thus, the SMA tendons can be disposed on and attached to the inner sides  64  of the exhaust mixing tabs  26  in any desirable geometry or pattern or any mixture of patterns based on the form the exhaust mixing tabs are desired to take on when the SMA tendons  26  are activated. Furthermore, the SMA tendons  34  may be attached to various exhaust mixing tabs  26  in a first pattern while other exhaust mixing tabs  26  have the SMA tendons  34  disposed on their inner sides  64  in a second pattern, based on the desired mixing of exhaust with the ambient air. Further yet, the number of SMA tendons  34  attached to each exhaust mixing tab  26  is determined based on the amount of deflection or deformation desired. That is, if a more severe deformation is desired, such that the exhaust mixing tabs  26  are deployed further into the exhaust flow, a greater number of SMA tendons  34  will be attached to each exhaust mixing tab  26 . Even further, the number of SMA tendons  34  attached to each exhaust mixing tab  26  can be different for various exhaust mixing tabs  26  included as part of a single nacelle  10 . 
   In a preferred implementation, a compliant coating  74 , shown in  FIG. 2 , is disposed across the inner side  64  and over the sleeves  58  of each SMA tendon  34 . The compliant coating  74  can be any material suitable for coating the inner sides of each exhaust mixing tab  26  and other nacelle components such that an aerodynamically smooth surface is created. For example, the compliant coating  74  could comprise an elastomer that is sufficiently flexible to allow the exhaust mixing tabs  26  to be deployed without adding any significant resistance. Additionally, the compliant coating  74  can comprise thermal insulation properties to protect the sleeves  58  and the SMA tendons  34  from being damaged by the bypass fan exhaust or other exhausts produced by the engine  14 . 
   The SMA tendons  34  have a predetermined length when secured to the inner sides  64  of the exhaust mixing tabs  26 . When the environment surrounding the SMA tendons  34  is below a transition temperature of the SMA tendons  34 , i.e. an actuation temperature, for example −20 to +20° F., the rigidity of the composite layer  54  is greater than that of forces applied to the exhaust mixing tabs  26  by SMA tendons  34 . Therefore, the rigidity of the composite layer  54  causing the SMA tendons  34  to be held taut across the inner sides  64 . This may also be referred to as the “martensitic” state of the SMA tendons  34  (i.e., the “cold” state). 
   When the environment surrounding the SMA tendons  34  is greater than the transition temperature, for example when the SMA tendons  34  are exposed to the bypass fan exhaust, the SMA tendons  34  are activated and constrict significantly (i.e., also known as its “austenitic” state). That is, the SMA tendons  34  shorten in length, which in turn causes the exhaust mixing tabs  26  to deploy, i.e. bend or deform into the exhaust gas flow  38 . In their activated condition, the forces applied by the SMA tendons  34  overcome the rigidity of the composite layer  54 , thus causing the exhaust mixing tabs  26  to deploy. Once the temperature of the surrounding environment cools and begins drops below the transition temperature, the rigidity of the composite layer  54  gradually overcomes the forces from the constricting, i.e. activated, SMA tendons  34 . This effectively “pulls” the SMA tendons  34  back to their original length and returns the exhaust mixing tabs  26  to their non-deployed position. Thus, the composite layer  54  acts as a ‘return spring’ to return the exhaust mixing tabs  26  to their non-deployed positions. It should be understood that the non-deployed position is when the exhaust mixing tabs  26  are positioned adjacent the exhaust flow path and not being deformed by the constriction of the SMA tendons  34  to extend into the exhaust flow path. 
   In an alternate preferred embodiment the composite layer  54  comprises a shape-memory allow such as nickel-titanium shape-memory alloy. An advantage of utilizing a super-elastic alloy is that it is extremely corrosion resistant and ideally suited for the harsh environment experienced adjacent the exhaust gas flow  38 . Also of significant importance is that it can accommodate the large amounts of strain required of the deformed shape. 
   In a preferred embodiment, the SMA tendons are heated using the exhaust gases from the secondary exhaust gas flow nozzle  22 . In actual operation, the heat provided by the exhaust gases emitted from the secondary exhaust gas flow nozzle  22  is typically sufficient in temperature (approximately 130 degrees Fahrenheit) to produce the needed constriction of the SMA tendons  34 . The actual degree of deformation may vary considerably depending upon the specific type of shape memory alloy used, as well as gauge or diameter of the SMA wire used to construct the SMA tendons  34 . When the aircraft reaches its cruising altitude, the significant drop in ambient temperature effectively acts to cool the SMA tendons  34 . The cooling of the SMA tendons  34  allows the composite layer  54  to stretch the SMA tendons  34  back to their non-activated length and exhaust mixing tabs  26  to return to their non-deployed positions. 
   In an alternative preferred embodiment, the SMA tendons  34  are heated by connecting the SMA tendons  34  to a controllable current source (not shown). To heat the SMA tendons  34  the current source is turned on such that current flows through the SMA tendons  34 . This causes the SMA tendons  34  to generate heat that in turn causes the the SMA tendons  34  to constrict significantly. As described above, this constriction of the SMA tendons  34  the exhaust mixing tabs  26  to deploy into the exhaust gas flow  38 . When it is desired that the exhaust mixing tabs  26  no longer be deployed, e.g. when the aircraft reaches cruising altitude, the current source is turned off. This allows the SMA tendons  34  cool so that the rigidity of the composite layer  54  gradually overcomes the constricting forces of the SMA tendons  34 , thereby returning the exhaust mixing tabs  26  to their non-deployed positions. 
   When each of the exhaust mixing tabs  26  is deployed, and thus protruding into the exhaust gas flow path  38 , the exhaust gas is intermixed with the ambient air flowing adjacent the secondary exhaust gas flow nozzle  22 . This intermixing produces a tangible degree of noise reduction. Most advantageously, as the aircraft reaches its cruise altitude, the retraction of the exhaust mixing tabs  26  to the non-deployed position, for example the exhaust mixing tabs  34  have essentially shape shown in  FIG. 2 , prevents the drag and loss of thrust that would otherwise be present if the exhaust mixing tabs  26  each remained deployed. 
   Referring to  FIG. 4 , in another preferred embodiment the primary exhaust nozzle  18  includes a plurality of exhaust mixing tabs  78  that extend from a lip area  82  of the primary flow nozzle  18 . SMA tendons are attached to the exhaust mixing tabs  78  in the same manner as described above with reference to SMA tendons  34  and exhaust mixing tabs  26 . The exhaust mixing tabs  78  and associated SMA tendons are essentially the same in form and function as the exhaust mixing tabs  26 , described above with reference to  FIGS. 1-3C , with the exception that the exhaust mixing tabs  78  deploy to increase the mixing of core exhausts, i.e. turbine exhaust, with the ambient air. Thus, although the above description of the present invention with respect to exhaust mixing tabs  26  will not be repeated with reference to exhaust mixing tabs  78 , it should be understood that exhaust mixing tabs  78  are deployed utilizing SMA tendons in essentially the identical manner as described above with reference to exhaust mixing tabs  26 . Furthermore, it should be understood that  FIGS. 2 ,  3 A,  3 B, and  3 C and the related description set forth above can be used to describe the present invention with reference to both exhaust mixing tabs  26  and  78 , with the understanding that the exhaust mixing tabs  78  are associated with the primary flow nozzle  18  while the exhaust mixing tabs  26  are associated with the secondary flow nozzle  22 . Furthermore, it should be understood when the embodiment described above, whereby the SMA tendons  34  are heated via the by-pass fan exhaust, is applied to the SMA tendons associated with the exhaust mixing tabs  78 , the core exhaust would be utilized to activate the exhaust mixing tabs  78  SMA tendons. 
   The preferred embodiments described herein thus provide deployable exhaust mixing tabs connected to the bypass fan exhaust nozzle, and/or the core exhaust nozzle. The exhaust mixing tabs are deployed, i.e. temporarily bent, into the exhaust flow(s) using shape memory tendons that constrict when activated to apply a one-dimensional linear force at an aft edge area of each exhaust mixing tabs. The constriction pulls on the aft edge area to bend each exhaust mixing tab into the respective exhaust flow(s), which provides a desired degree of noise attenuation provided upon takeoff of an aircraft. Additionally, the preferred embodiments allow unobstructed or accelerating exhaust gas flow from the secondary and/or primary exhaust gas nozzle(s) when the aircraft is operating at a cruise altitude. Due to the use of SMA actuators, the preferred embodiments of the invention do not add significant weight to the engine nacelle nor do they unnecessarily complicate the construction of the nacelle. 
   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.