Abstract:
An arcuate or semi-circumferential shield in the shape of a visor that is adapted to be secured to an external surface of a nozzle housing of a jet nozzle to attenuate jet noise generated by the jet nozzle. The shield may be fixedly secured to the nozzle housing or movably supported so that it can be moved between retracted and deployed positions. When used as a fixedly mounted component, or when positioned in its deployed position, a downstream edge of the shield extends past a downstream edge of the nozzle housing and the shield is spaced apart from an outer surface of the nozzle housing to form a channel therebetween. The shield is preferably orientated at approximately a bottom dead center of the nozzle housing. The shield operates to attenuate jet installation noise, and particularly jet installation noise experienced during the takeoff phase of flight of a jet aircraft, as well as to reduce jet installation noise that would otherwise propagate forwardly toward the cockpit of the aircraft.

Description:
FIELD 
     The present disclosure relates to nozzles for jet engines, and more particularly to a nozzle housing that houses a jet engine, where the nozzle housing includes a noise attenuating shield for attenuating noise. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     The noise a jet engine makes when it is installed under the wing of an airplane can be broken down into components. Two of the most significant components are jet noise and jet installation noise. Jet noise is the noise the jet makes and that it would make whether or not it is installed on an aircraft. Jet installation noise is the additional noise the jet makes due to the presence of the wing and flap system of the aircraft. Jet installation noise is a significant consideration for present day commercial passenger transport and freighter jet aircraft when the engines are installed under the wings. 
     At the present time, with new aircraft development, jet installation noise may limit or influence a wide variety of component design factors. Components that might be design influenced or limited in some manner because of the expected or anticipated influence of jet installation noise may involve one or more of the following:
         restricting fan diameter;   lengthening landing gear;   increasing wing dihedral angle;   decreasing flap angle, which produces reduced low speed aerodynamic performance;   impacts to wing trailing edge design;   longer and heavier engine strut; and   affecting aircraft balance and loading.       

     The use of chevron type nozzles is currently the principally accepted way of achieving jet noise reduction on an existing jet engine without a significantly large weight and performance penalty. Chevron nozzles are triangular shaped devices installed on the downstream edge of the jet engine fan and primary exhaust nozzles. The chevrons increase mixing of the flow leaving the nozzle with ambient air and reduce jet noise. In addition recent work has also shown that the chevrons can reduce jet installation noise as well, which is a major component of aircraft noise. Typical chevron design reduces low frequency noise but can in some instances produce some increase in high frequency noise. This increase in high frequency noise is typically in the forward radiation angles (as measured from the engine inlet axis, or forwardly toward the nose of the aircraft). 
     Thus, it would be highly beneficial and desirable to provide a jet nozzle that operates to reduce jet installation noise, as well as to inhibit the radiation of high frequency jet installation noise that is generated close to the downstream exit of the nozzle that would ordinarily tend to propagate forwardly toward the nose of an aircraft. 
     SUMMARY 
     The present disclosure relates to a jet nozzle apparatus and method that significantly attenuates jet installation noise on a jet aircraft. In one embodiment the apparatus includes a nozzle housing having an outer surface. A shield is disposed adjacent the outer surface and a downstream edge of the shield extends past a downstream edge of the nozzle housing. The shield is also mounted so as to be spaced apart from the outer surface of the nozzle housing to form a channel between an inner surface of the shield and the outer surface of the nozzle housing. 
     In one specific embodiment the shield is fixedly mounted on the exterior surface of the housing such that it is not movable. In another embodiment the shield is movably mounted so that it may be moved between retracted and deployed positions. In its retracted position, the shield is held closely adjacent the outer surface of the nozzle housing so that the channel is substantially or completely eliminated. In its deployed position the shield is moved to a position where its downstream edge extends in a downstream direction past the downstream edge of the nozzle housing. Various forms of actuators such as electromechanical, hydraulic or shape memory alloy (SMA) actuators may be employed to move the shield. 
     In one embodiment the shield has a generally circumferential shape when viewed end-wise, and is shaped generally similar to a visor. 
     In one embodiment the shield is positioned at approximately a bottom dead center location of the nozzle housing. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  illustrates a commercial jet passenger aircraft with a nozzle apparatus in accordance with one embodiment of the present disclosure incorporated thereon; 
         FIG. 2  is an enlarged, rear three-quarter perspective view of just the nozzle apparatus shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of just the shield shown in  FIG. 1 ; 
         FIG. 4  is a side view of the apparatus shown in  FIG. 1 ; 
         FIG. 5  is a rear view of the nozzle apparatus of  FIG. 2 ; 
         FIG. 6  is a side view of another embodiment of the present nozzle apparatus that incorporates a shield that is movable between retracted and deployed positions, with the shield being illustrated in its deployed position; 
         FIG. 7  illustrates the apparatus of  FIG. 6  but with the shield shown in its retracted position; and 
         FIG. 8  is a graph illustrating a reduction in jet installation noise provided by one embodiment of the nozzle apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring to  FIG. 1 , a nozzle apparatus  10  is illustrated in use on a commercial passenger jet aircraft  12 . While a commercial passenger jet aircraft is shown, it will be appreciated that the nozzle apparatus  10  can be used on freighter jet aircraft or even on military jet aircraft. The nozzle apparatus  10  is expected to find utility on other forms of jet powered mobile platforms, for example jet powered rotorcraft, as well. It is anticipated that the nozzle apparatus  10  may find applicability with essentially any form of jet powered mobile platform where it is desirable to reduce jet installation noise. 
     Referring further to  FIGS. 2 ,  3  and  4 , the nozzle apparatus  10  is shown in further detail. The nozzle apparatus  10  includes a flow control structure  14  which in one embodiment has an arcuate shape, and may be viewed as forming a shield. Merely for convenience, the flow control structure  14  will be referred throughout the following description as “shield  14 ”. In one specific embodiment, the arcuate shape of the shield  14  forms a semi-circumferential shape. However, the shield  14  can have other shapes including a flat shape if desired. 
     The shield  14  is preferably at least slightly larger than the outer diameter of a nozzle housing  16  of the nozzle apparatus  10  at a downstream end  16   a  of the nozzle housing  16 . This enables a channel  18  ( FIG. 2 ) to be formed between an outer surface  20  of the nozzle housing  16 , which in this example is a fan or “secondary” nozzle housing, and an inner surface  22  of the shield  14  when the shield is attached to the nozzle housing  16 . Although the shield  14  is shown extending halfway around the nozzle housing  16 , it is understood that it could have a shorter or longer circumferential extent. The shield  14  preferably has a one-piece continuous construction, but could be two or more pieces in spaced or attached relation. Still further, it is expected that in most applications, forming the shield  14  as a solid barrier will be a preferred construction, rather than of a porous construction that allows a portion of air flowing thereover to flow through the shield. Nevertheless, in some limited applications, a porous construction may provide some benefit, and is therefore also contemplated to be within the realm of the present disclosure. 
     It is also contemplated to be within the scope of the present disclosure that the shield  14  could just as readily be secured to the exterior surface of a primary nozzle  24  illustrated in  FIG. 2 . At the present time, however, it is anticipated that the mounting of the shield  14  on the outer surface of a fan nozzle will be the preferred construction in most applications to maximize jet installation noise attenuation. Also, both the nozzle housing  16  and the primary nozzle  24  can be seen to each include a plurality of chevrons  16   b  and  24   a,  respectively. But the nozzle apparatus  10  could just as readily be constructed without any chevrons. The shield  14  is therefore equally applicable, and effective for reducing noise, in nozzle apparatuses that do not use chevrons. Incorporating the chevrons  16   b  and  24   a,  however, may optimize the jet installation noise reduction that is provided by the nozzle apparatus  10 . This is due to the chevrons providing jet noise and jet installation noise reduction by providing better mixing of the jet flow leaving the nozzle apparatus  10 . The nozzle apparatus  10  thus provides noise reduction over and above the reduction that the chevrons provide. This will be discussed further in the following paragraphs in connection with  FIG. 8 . 
     With further reference to  FIGS. 3-5 , the shield  14  can be seen in greater detail. In this exemplary embodiment the shield  14  includes a central portion  26  from which a pair of symmetric, spaced apart arms  28  extend. The entire shield  14  may be constructed with a honeycomb acoustic treatment, or any other form of sound attenuating material that is suitable for high environmental stress applications. The honeycomb acoustic material construction helps to attenuate the forwardly radiated high frequency noise. However, the shield  14  can be used without any specific sound attenuating material construction, or alternatively could simply be coated with a suitable sound attenuation material and will still operate to significantly attenuate jet installation noise. 
     The arms  28  are coupled to a pair of spacers  30  ( FIG. 5 ). The spacers  30  are in turn fixedly coupled to the outer surface  20  of the nozzle housing  16 . Any suitable fastening elements, for example rivets, may be used to secure the arms  28  and spacers  30  to the nozzle housing  16 . The central portion  26  is supported by at least one strut  32  or strut-like element, and more preferably a pair of struts  32 . The struts  32  are each fixedly coupled at opposite ends to the inner surface  22  of the shield  14  and to the exterior surface  20  of the nozzle housing  16 . Alternatively, the struts  32  could each have one end that extends through a small opening in the nozzle housing  16  and be secured fixedly to an interior surface of the nozzle housing  16 . Essentially any arrangement of components that are able to securely hold the shield  14  to the nozzle housing  16  may be employed. Accordingly, the nozzle apparatus  10  is not limited to only one type of mounting arrangement. 
     With further reference to  FIGS. 3-5 , the shield  14  can be seen to have a shape that is similar to a visor with a generally semi-cylindrical shape when viewed end-wise. While the shield  14  is shown as having a semi-cylindrical shape that is not of a constant radius, forming the shield  14  to have a constant radius, or other shapes, is also contemplated to be within the present disclosure. With either construction, the channel  18  operates to separate the exterior surface  20  of the nozzle housing  16  at the downstream end  16   a  from the interior surface  22  of the shield  14  by preferably about 1/12 of the nozzle housing  16  diameter (i.e., the diameter of the “secondary nozzle”). The shield  18  is preferably also mounted such that it is located at approximately a bottom dead center of the nozzle housing  16  to maximize its ability to impede noise from propagating forwardly. It will be appreciated, however, that other locations for the shield  14  could be selected as needed to address particular noise control or integration issues. 
     The shield  14  may be formed from aluminum, from composites or any other suitable material that is sufficiently robust to handle the severe environmental conditions that the shield  14  will be exposed to. In one embodiment the shield  14  may have a honeycomb construction, as indicated at  14   a  in  FIG. 3 . The shield  14  may have a thickness of preferably between about one inch to about three inches (2.54 cm-7.62 cm), but this may be varied significantly depending on the specific materials used to form the shield  14 , as well as the needs of a particular application. 
     In operation, it is believed that the significant degree of jet installation noise sound attenuation that is achieved with the shield  14  is caused in significant part by the channel  18 . It is believed that the channel  18  accelerates the air flow (i.e., fluid flow) through the channel exiting from the outer, downstream edge  16   a  of the nozzle housing  16 . This in turn is believed to reduce the shear layer on the bottom half of the nozzle apparatus  10 , and to alter the local pressure distribution, which effectively “pulls” the fluid flow leaving the nozzle apparatus  10  downwardly away from the flaps on the wing of the aircraft  12 . Impingement of the fluid flow (also termed “jet flow”) from the nozzle apparatus  10  on the flaps, the lower surfaces of the wings, and even the fuselage is known to contribute significantly to jet installation noise. Thus, it is believed that redirecting or “pulling” the fluid flow leaving the nozzle apparatus  10  away from the aircraft  12  significantly reduces its impingement (or “scrubbing”) on various surfaces of the aircraft. By doing this the shield  14  also reduces the low frequency (50-400 Hz) jet installation noise. The shield  14 , when constructed of a honeycomb construction or otherwise acoustically treated, also has a particular benefit in reducing the propagation of high frequency (i.e., typically about 1 kHz or higher) noise forwardly towards the cockpit of the aircraft  12 . 
     With brief reference to  FIG. 8 , the reduction in jet installation noise with the nozzle apparatus  10  is shown.  FIG. 8  illustrates sound power levels experienced with: 1) a baseline approach (i.e., without the chevrons  16   b  and  24   a,  and without the shield  14 ) indicated by curve  40 ; 2) an otherwise conventional jet nozzle having the chevrons  16   b  and  24   a,  represented by curve  42 ; and 3) the nozzle apparatus  10 , as represented by curve  44 . From the above-mentioned curves, it can be seen that with the nozzle apparatus  10  there is a reduction in sound power that corresponds to an approximate 2 dB installation noise level reduction over a conventional jet nozzle that uses chevrons, and a reduction in sound power that corresponds to an approximate 4 dB reduction over a conventional jet nozzle that does not use chevrons. 
     Referring to  FIGS. 6 and 7 , another nozzle apparatus  100  in accordance with the present disclosure is shown. The apparatus  100  is similar to nozzle apparatus  10  and common components are identified by reference numerals increased by 100 over those used to describe the apparatus  10 . The principal difference between nozzle apparatus  10  and nozzle apparatus  100  is that nozzle apparatus  100  includes a shield  114  that is movably supported relative to its nozzle housing  116 . This is accomplished by supporting the shield  114  by a plurality of struts  132  that may be similar in construction to struts  32 . Each strut  132  may be formed as a component of an electromechanical actuator, a hydraulic actuator or even from a shape memory alloy (SMA) material. The struts  132  serve to move the shield  114  in a generally linear fashion upwardly relative to a longitudinal centerline  150  of the nozzle apparatus  100 , and forwardly in accordance with directional arrow  152  (i.e., toward the cockpit of the aircraft). The shield  114  is shown in its deployed position in  FIG. 6  and its retracted position in  FIG. 7 . In the fully retracted position the shield  114  has no affect on the jet flow exiting the nozzle apparatus  100 . If SMA actuators are used, the SMA material may be constructed so that the SMA actuators change shape to automatically deploy and retract the shield  114  in response to predetermined temperatures that are experienced by the shield  114 . 
     The various embodiments of the system and method described herein thus enable jet installation noise to be significantly reduced. Furthermore, while various embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the present disclosure. The examples illustrate the various embodiments and are not intended to limit the present disclosure. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.