Abstract:
An exhaust flow nozzle for a jet engine having a plurality of flow altering components extending from a lip portion of a secondary exhaust nozzle that are movable between first and second positions. In the first position the flow altering components are disposed substantially parallel to an exhaust gas flow path and thereby do not produce drag or a reduction of thrust from the engine. In the second position the flow altering components bend or are deformed to project into the exhaust gas flow path exiting from the secondary exhaust nozzle. The flow altering components are comprised of a shape-memory alloy material which deforms in response to heat. One or more additional layers of material are bonded or otherwise coupled to the shape-memory alloy layer of each flow altering component to assist in returning the shape-memory alloy layer to its unheated shape.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to noise suppression devices used with jet engines, and more particularly to a deployable, segmented exhaust nozzle for attenuating the noise produced by a jet engine.  
         BACKGROUND OF THE INVENTION  
         [0002]    With present day jet aircraft, structure typically known in the industry as “chevrons” have been used to help in suppressing 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 secondary exhaust nozzle of the jet engine such that they project into the exhaust gas flow stream exiting from the secondary 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 a wide range of 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.  
           [0003]    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 low cost operation during cruise.  
           [0004]    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.  
         SUMMARY OF THE INVENTION  
         [0005]    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 flow altering components spaced apart from one another and extending from a lip of an exhaust nozzle of a jet engine adjacent a flow path of an exhaust flow emitted from the exhaust nozzle. Each of the exhaust flow altering components 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 flow altering components. In the first position, the flow altering components 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 flow altering components are deformed to extend into the flow path. In this position the flow altering components promote mixing of the exhaust flow with an adjacent air flow. This results in the attenuation of noise generated by the jet engine.  
           [0006]    In one preferred form each of the flow altering components comprises a heat sensitive layer of prestressed, shape-memory material which responds to the exhaust flow (i.e., the control signal) by deforming such that it bends to project into the exhaust flow path when in the second position. In one preferred embodiment the shape-memory material comprises an alloy of nickel and titanium.  
           [0007]    In another preferred embodiment a conductor is included in the flow altering component which allows an electrical current (i.e., the control signal) to be flowed through the flow altering component. The electrical current generates the heat needed to deform the flow altering component so that it can be moved into the second position.  
           [0008]    In the above described embodiments, a second piece of material also is disposed adjacent the layer of prestressed, shape-memory material to act as a return “spring”. The second layer of material assists in returning the shape-memory material into the first position when the control signal is removed therefrom.  
           [0009]    In the above-described embodiment which relies on the heat generated by the exhaust gas flow, the level of heat experienced during takeoff is sufficient to effect the deformation, and thus the deployment, of the flow altering components. As the aircraft reaches a cruise altitude, the significant cooling experienced by the flow altering components allows the flow altering components to be returned to their non-deformed (and thus non-deployed) orientations coinciding with the first position described above.  
           [0010]    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 limited the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 is a simplified side view of a nacelle for housing a jet engine of an aircraft, with the nacelle incorporating the flow altering components of the present invention along a trailing circumferential lip portion of the secondary exhaust nozzle of the nacelle;  
         [0013]    [0013]FIG. 2 is a partial side view of one of the flow altering components taken in accordance with section line  2 - 2  in FIG. 1;  
         [0014]    [0014]FIG. 3 is a simplified side view of the two layers of material used to form the flow altering component, in one preferred form;  
         [0015]    [0015]FIG. 4 is a simplified side view of the two materials of FIG. 3 after having been bonded together;  
         [0016]    [0016]FIG. 5 is a simplified side view of a portion of the flow altering component illustrating the deformation produced in response to heat experienced by the shape-memory alloy layer of the flow altering component;  
         [0017]    [0017]FIG. 6 is a view of an alternative preferred embodiment of one of the flow altering components of the present invention;  
         [0018]    [0018]FIG. 7 is a cross sectional side view of the flow altering component of FIG. 6 taken in accordance with section line  7 - 7  in FIG. 6;  
         [0019]    [0019]FIG. 8 is another alternative preferred form of the flow altering component of the present invention; and  
         [0020]    [0020]FIG. 9 is a cross sectional side view of the flow altering component of FIG. 8 taken in accordance with section line  9 - 9  in FIG. 8. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0022]    Referring to FIG. 1, there is shown an engine nacelle  10  for housing a jet engine  10   a . The nacelle  10  includes a primary exhaust gas flow nozzle  12  and a secondary exhaust gas flow nozzle  14 . A plug  11  is disposed within the nacelle  10 . The secondary exhaust flow nozzle  14  includes a plurality of flow altering components  16  in accordance with a preferred embodiment of the present invention. The flow altering components  16  extend from a lip area  18  of the secondary flow nozzle  14 . As will be described in greater detail in the following paragraphs, each of the flow altering components  16  operates to deform (i.e., bend or deflect) in response to heat such that they extend (i.e., “deploy”) partially into the exhaust gas flow path exiting from the secondary exhaust gas flow nozzle  14 . This is indicated by dashed lines  16   a  on the uppermost and lowermost flow altering components  16  in the drawing of FIG. 1. The flow altering components  16  are preferably arranged circumferentially around the entire lip portion  18  of the secondary exhaust gas flow nozzle  14 .  
         [0023]    Referring to FIG. 2, a portion of one of the flow altering components  16  is illustrated. It will be appreciated that in the industry the flow altering components  16  are often referred to as “chevrons”. However, it should be appreciated that while the term “chevron” implies a triangular shape, the flow altering components  16  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 flow altering components  16  each include a tab portion  20 , a root portion  22  and a nozzle extension portion  24 . The nozzle extension portion is used to secure the flow altering component  16  to the lip portion  18  of the secondary exhaust flow nozzle  14 . The tab portion  20  is the principal portion that projects into the exhaust gas flow path discharged from the secondary exhaust gas flow nozzle  14 . The lip area  22  forms an intermediate area for transitioning from the tab portion  20  to the nozzle extension portion  24 . The nozzle extension portion  24  can be secured with rivets or any other suitable securing means to the lip portion  18  of the secondary exhaust gas flow nozzle  14 .  
         [0024]    Referring now to FIG. 3, the flow altering component  16  is formed by a layer of heat sensitive, prestressed shape-memory alloy material  26  which is bonded or otherwise suitably secured to a layer of metal such as, for example, aluminum  28 . In one preferred form the shape-memory alloy  26  comprises a nickel-titanium alloy. More preferably, the nickel-titanium alloy NiTinol™ is used for the shape-memory alloy layer  26 . It is important to note that the shape-memory alloy  26  is formed so as to be prestressed with a desired degree of curvature illustrated in FIG. 3. This is the curvature that the shape-memory alloy layer  26  will assume when it is heated by the exhaust gas flow emitted from the secondary exhaust gas flow nozzle  14  and deforms into its deployed position. The curvature needs to be sufficient to allow the layer  26  to project into the exhaust gas flow path once it is heated.  
         [0025]    The overall thickness of the layer  26  at the tab portion  20  may vary, but in one preferred from it is preferably between about 0.05″-0.25″ (1.27 mm-6.35 mm), and more preferably about 0.15″ (3.81 mm). At the root portion  22  the overall thickness is preferably between about 0.15″-0.35″ (3.81 mm-8.89 mm), and more preferably about 0.25″ (6.35 mm). The thickness of the shape memory alloy layer  26  is preferably between about 0.15″-0.20″ (3.81 mm-5.08 mm). It will be appreciated that all of the above-mentioned dimensional ranges could be varied further to suit the needs of a specific application.  
         [0026]    Referring to FIG. 4, the shape-memory alloy layer  26  assumes a generally preset shape once secured to the metal layer  28 . This is because when the shape-memory alloy layer  26  is not being heated, the strength of the metal layer  28  is greater than that of the shape-memory alloy  26 , thus causing the shape-memory alloy layer  26  to be straightened into the position shown in FIG. 4. This may also be referred to as the “martensitic” shape of the shape-memory alloy layer  26  (i.e., its “cold” shape).  
         [0027]    When the shape-memory alloy layer  26  experiences heat, indicated by exhaust gas flow arrow  30 , the modulus of elasticity of the shape-memory alloy  26  increases significantly, thus causing the layer  26  to bend or deform into the exhaust gas flow  30 . If NiTinol™ alloy is used as the shape-memory alloy layer  26 , its modulus of elasticity will increase by a factor of about three when it is in its “hot” state (i.e., also known as its “austenitic” state). In its heated condition, the modulus of elasticity of the shape-memory alloy layer  26  overcomes the modulus of elasticity of the metal layer  28 , thus causing the deformation shown in FIG. 5. Once the heat source is removed, the metal layer  28  gradually overcomes the modulus of elasticity of the shape-memory alloy layer  26  as layer  26  cools, thus effectively “pulling” the shape-memory alloy layer  26  back into the position shown in FIG. 4.  
         [0028]    In actual operation, the heat provided by the exhaust gases emitted from the secondary exhaust gas flow nozzle  14  is typically sufficient in temperature (approximately 130 degrees Fahrenheit) to produce the needed deformation of the shape-memory alloy layer  26 . The actual degree of deformation may vary considerably depending upon the specific type of shape memory alloy used, as well as its thickness, but the preferred embodiments described herein deflect between about 0.5″-1.0″ (12.7 mm-25.4 mm) when activated.  
         [0029]    When the aircraft reaches its cruising altitude, the significant drop in ambient temperature effectively acts to cool the shape-memory alloy layer  26 , thus allowing the metal layer  28  to gradually return the shape-memory alloy layer  26  to the position shown in FIG. 4. When in the position shown in FIG. 5, each of the flow altering components  16  is deployed, and thus protruding into the exhaust gas flow path  30 , thus causing intermixing of the exhaust gas with the ambient air flowing adjacent the secondary exhaust gas flow nozzle  14 . This intermixing produces a tangible degree of noise reduction. Most advantageously, as the aircraft reaches its cruise altitude, the retraction of the flow altering components  16  to the orientation shown in FIG. 4 prevents the drag and loss of thrust that would otherwise be present if the flow altering components  16  each remained in a deformed (i.e., deployed) condition.  
         [0030]    Referring now to FIG. 6, a flow altering component  40  in accordance with an alternative preferred embodiment of the present invention is shown. It will be appreciated that a plurality of flow altering components  40  are secured to the lip portion  18  of the secondary flow nozzle  14  so as to be spaced circumferentially about the secondary flow nozzle  14 , just as described in connection with flow altering components  16 . Each flow altering component  40  includes a layer of composite material  42  having a recessed area  44  upon which is secured a shape-memory alloy layer  46 . The layers  44  and  46  are secured together via double countersunk ASP fasteners  48  inserted within appropriately formed holes in each of the layers  42  and  46 . Layer  46  may comprise NiTinol™ alloy. A layer  50  of super-elastic nickel-titanium alloy, preferably “NiTinol™  60 ” alloy, is also secured to the shape-memory alloy layer  46  by a plurality of double flush rivets  52  joining layers  46  and  50 . It will be appreciated immediately, however, that other forms of attachment could be employed, such as adhesives. The super-elastic alloy layer  50  is also relieved at area  52  to provide clearance for a conductor  54  which is sandwiched between the super-elastic alloy layer  50  and the shape-memory alloy layer  46 . The conductor  54  may comprise an electrical conductor which is coupled to a suitable source of electrical current (not shown). The conductor  54  operates to provide heat to the shape-memory alloy layer  46  to thereby cause the deformation of the flow altering component  40  into the deployed position indicated in dashed lines relative to the exhaust gas flow  30 . One important advantage of using the super-elastic  60  as the alloy layer  50  is that it is extremely corrosion resistant and ideally suited for the harsh environment experienced adjacent the exhaust gas flow  30 . Also of significant importance is that it can accommodate the large amounts of strain required of the deformed shape. The super-elastic alloy layer  50  performs the biasing function of the metal layer  28  described in connection with FIGS.  3 - 5  to gradually return the shape-memory alloy layer  46  to the position shown in solid lines in FIG. 7 when the conductor  54  is not providing heat to the shape-memory alloy layer  46 .  
         [0031]    Referring now to FIGS. 8 and 9, a flow altering component  60  in accordance with another alternative preferred embodiment of the present invention is shown. The flow altering component  60  also comprises a composite layer  62  which is secured to a shape-memory alloy layer  64  by a plurality of removable, double countersunk ASP fasteners  66 . Also secured to the composite layer  62  is a strake  68  which is secured via suitable fasteners  70  (or possibly via an adhesive) to the composite layer  62 . In this embodiment the shape-memory alloy layer  64  is “trained” during manufacture to assume one position when it is heated, indicated by the dashed lines in FIG. 9, and a second position when it is not being heated, indicated in solid lines in FIG. 9. The strake  68  acts as a stop to limit return or retracting movement of the shape-memory alloy layer  64  as it cools down from a heated condition.  
         [0032]    The preferred embodiments described herein thus provide a deployable flow altering component which allows a desired degree of noise attenuation to be provided upon takeoff of an aircraft, while also allowing unobstructed or accelerating exhaust gas flow from a secondary exhaust gas nozzle when the aircraft is operating at a cruise altitude. 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.  
         [0033]    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.