US20040068981A1 - Exhaust mixer and apparatus using same - Google Patents

Abstract

Disclosed is an exhaust mixer (50) including a passage (54) extending from an inlet (56) to an outlet (58) that is coincident with a centerline axis of mixer (50). Several ridges (68) are circumferentially disposed about the axis and each flare away from the centerline axis relative to a direction along the centerline axis from inlet (56) toward outlet (58). Ridges (68) each define a corresponding one of several inner channels (74) radially disposed about passage (54) that each intersect passage (54) between inlet (56) and outlet (58). Several outer channels (84) are also radially disposed about passage (54) and are each positioned between a corresponding pair of inner channels (74). Ridges are each shaped to turn inner channels (74and outer channels (84) about the axis as ridges (68) extend along the indicated direction. Inner channels (74) diverge away from the axis and one another in this direction while outer channels (84) converge toward the axis and one another in this direction.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• The present application claims the benefit of U.S. Provisional Patent Application serial No. 60/114,623 filed 4 Jan. 1999, which is hereby incorporated by reference.[0001]
BACKGROUND
• The present invention relates to exhaust mixers, and more particularly, but not exclusively, relates to an exhaust mixer for a gas turbine engine that reduces the visibility of hot parts.[0002]
• It is often desirable to mix exhaust from a gas turbine engine with cooler air. Such mixing is often utilized to reduce the noise level generated by gas turbine engines especially those used to propel aircraft. Several devices to facilitate mixing have been developed that are placed in the path of exhaust exiting the engine; however, in many applications, these devices leave room for improvement.[0003]
• Furthermore, in certain applications, it is desirable to reduce visibility of hot parts of the engine through the mixing device. Alternatively or additionally, it may also be desirable to block view of the hot regions of the device itself.[0004]
• Accordingly, there is a demand for further contributions in this area of technology.[0005]
SUMMARY
• One form of the present invention is a mixer with improved line-of-sight blockage.[0006]
• In an alternative form, an improved mixer has a number of lobes each shaped to block at least a portion of the hot inner surface of the mixer or hot parts of the exhaust portion of an engine coupled to the mixer. Preferably, the lobes are curved in a pattern selected to provide a desired degree of blockage. More preferably, the lobes generally twist about a reference axis corresponding to the mixer, such as the mixer's centerline axis. However, in other embodiments of the present invention, the lobes may be shaped or oriented differently.[0007]
• In another form, a mixer includes a number of radial lobes that each terminate in a radial end wall or fin. The mixer may include lobes that twist about an axis corresponding to the direction of working fluid flow through the mixer. The walls may include a curved edge to direct working fluid towards a centerline axis of the mixer. However, in other embodiments, the walls may be shaped differently in accordance with the present invention.[0008]
• In still another form, a mixer is provided that includes a number of radially oriented troughs and a number of structures that each extend from a corresponding one of the troughs toward the centerline of the mixer. These structures may be in the form of fins or vanes that at least partially block hot parts. The mixer may alternatively or additionally include a curved or twisting pattern of the troughs relative to a reference axis to enhance line-of-sight blockage. For embodiments of the present invention including the structures extending toward the center of the mixer, these structures may also be arranged in a curved or twisted pattern.[0009]
• In a further form, a multilobed mixer includes a number of hollow radial vanes that extend from troughs between adjacent pairs of the mixer lobes toward the center of the mixer to provide cooling fluid. The cooling fluid may be utilized to cool a centerbody of an associated engine. The mixer may additionally or alternatively include a curved or twisting pattern of lobes relative to a reference axis to enhance line-of-sight blockage. For embodiments of the present invention that include the vanes, the vanes may also be oriented or shaped to follow a curved or twisted pattern.[0010]
• In other forms of the present invention, a mixer according to the present invention may be coupled to an engine used to propel a vehicle. The vehicle may be an aircraft with the engine being of the gas turbine variety. In other embodiments, the mixer of the present invention is employed with a different vehicle type, such a land vehicle or a vessel that travels on or through the water. Also, a mixer according to the present invention may be utilized with any engine type as would occur to those skilled in the art.[0011]
• Further forms, embodiments, objects, features, advantages, benefits, and aspects of the present invention shall become apparent from the drawings and description provided herein.[0012]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a side view of a first embodiment of the present invention.[0013]
• FIG. 2 is a partial sectional, side view of the exhaust mixing system shown in FIG. 1.[0014]
• FIG. 3 is an end, elevational view of the exhaust mixer shown in FIG. 2.[0015]
• FIG. 4 is a top left, isometric view of the exhaust mixer shown in FIG. 2.[0016]
• FIG. 5 is a top left, perspective view of the exhaust mixer shown in FIG. 2 along a different line of sight than FIG. 4.[0017]
• FIG. 5A is a schematic representation of the rotation about axis F of path P shown in FIG. 5.[0018]
• FIG. 6 is a side, elevational view of an exhaust mixer of a second embodiment of the present invention.[0019]
• FIG. 7 is an end, elevational view of the embodiment of FIG. 6.[0020]
• FIG. 8 is a top left, isometric view of the embodiment of FIG. 6.[0021]
• FIG. 9 is a side, elevational view of an exhaust mixer of a third embodiment of the present invention.[0022]
• FIG. 10 is an end, elevational view of the embodiment of FIG. 9.[0023]
• FIG. 11 is a top left, isometric view of the embodiment of FIG. 9.[0024]
• FIG. 12 is an end, elevational view of an exhaust mixer of a fourth embodiment of the present invention.[0025]
• FIG. 13 is a partial sectional, end view of the embodiment of FIG. 12.[0026]
• FIG. 14 is a top left, isometric view of the embodiment of FIG. 12.[0027]
• FIG. 15 is an end, elevational view of an exhaust mixer of a fifth embodiment of the present invention.[0028]
• FIG. 16 is a partial sectional, end view of the embodiment of FIG. 15.[0029]
• FIG. 17 is a top left, isometric view of the embodiment of FIG. 15.[0030]
• FIG. 18 is an end, elevational view of an exhaust mixer of a sixth embodiment of the present invention.[0031]
• FIG. 19 is a partial sectional, end view of the embodiment of FIG. 18.[0032]
• FIG. 20 is a top left, isometric view of the embodiment of FIG. 18.[0033]
DESCRIPTION OF SELECTED EMBODIMENTS
• For the purposes of promoting an understanding of the principles of the invention, reference will now be made to various embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.[0034]
• One embodiment of the present invention is shown in FIG. 1 as[0035]aircraft20.Aircraft20 includesfuselage22 andwing24. Turboprop30 is mounted towing24 and includesgas turbine engine32 withintake34. Exhaust produced byengine32 flows along an exhaust pathway and exits atdischarge36.Mixing system40 is provided along this exhaust pathway. Mixingsystem40 includesduct42 definingdischarge36, and mixer50 (shown in phantom) positioned induct42.
• Referring additionally to FIG. 2, a partial sectional, side view of mixing[0036]system40 is illustrated.Mixer50 includesconduit52 positioned induct42 about centerlineaxis F. Conduit52 includespassage54 extending frominlet56 defined byconduit end portion57 tooutlet58 defined byconduit end portion59.Inlet56 is positionedopposite outlet58 along axis F, and at least a portion ofpassage54 is coincident with axis F, such that axis F passes through the center ofinlet56 andoutlet58.Mixer50 is coupled togas turbine engine32 along axis F.Gas turbine engine32 is partially shown in FIG. 2 withturbine33 havingblades35 positioned in annular workingfluid passage37.Passage37 is defined byengine casing38.Casing38 is sized to fit withinduct42 and is coupled tomixer50 to aligninlet56 withpassage37.Engine32 is extended bycenterbody39 that entersmixer50 throughinlet56, and terminates inconduit52 ofmixer50.
• [0037]Gas turbine engine32 operates in the standard manner, receiving air throughintake34 for pressurization by one or more compressors rotating about axis F (not shown). At least a portion of this pressurized air is mixed with fuel to provide a fuel charge that is combusted to release energy in the form of hot, expanding gases. These combustion gases impinge on one or more turbines, such asturbine33 shown in FIG. 2, causing the one or more turbines to rotate about axis F. The mechanical power provided by turbine rotation is used to do work, such as propelaircraft20. Also, rotation of each of the one or more compressors is typically maintained by a rotatable coupling to a corresponding turbine; thereby continuing the supply of pressurized air to sustain combustion.
• It should be understood that[0038]gas turbine engine32 may include a number of other components that are not shown to enhance clarity. Further, any compressors and/or turbines ofgas turbine engine32 may be of a single or multi-stage variety. Alternatively or additionally,gas turbine engine32 may include multiple spools each comprised of a compressor rotatably coupled by a shaft to a turbine. In one common “dual spool” configuration, the shafts of two spools are arranged concentric to one another to correspondingly provide a low pressure or fan stage compressor upstream of a high pressure compressor, with a corresponding pair of turbines to drive the low and high pressure stages. In another configuration,gas turbine engine32 also includes a turbine that is not coupled to a compressor and accordingly is capable of rotating freely relative to any compressor. This free turbine is typically arranged to turn a shaft for delivering mechanical power, and is commonly used in turboprop and helicopter applications.
• In still another embodiment,[0039]gas turbine engine32 is arranged to propel a vehicle with the thrust produced by discharging a working fluid jet through a nozzle.Duct42 can be arranged to provide a suitable nozzle for such embodiments. Indeed, in other embodiments of the present invention, mixingsystem40 is used with different varieties of engines either in addition or as an alternative to the gas turbine type. These different types may include pulse detonation engines, wave rotor engines, ram jets, internal combustion engines of the reciprocating piston variety, internal combustion engines of the intermittent Spark Ignition (SI) or Compression Ignition (CI) variety, and/or hybrid combinations of such engine types, just to name a few.
• During engine operation,[0040]inlet56 ofmixer50 is arranged to receive hot exhaust gases for intermixing with relatively cooler gases before being discharged throughdischarge36. In FIG. 2, the hot exhaust flow fromengine32 is designated by arrows EF.Inlet56 ofpassage54 is in fluid communication withpassage37 to receive exhaust flow EF. An outside stream of cooling fluid, as designated in FIG. 2 by arrows CF, flows betweenduct42 andconduit52 ofmixer50 to be mixed with exhaust flow EF atoutlet58. Typically, this cooling fluid is air from an outside inlet, compressor stage, or fan stage ofengine32.
• Referring further to the end elevational view of FIG. 3; the top left isometric view of FIG. 4; and the top left perspective view of FIG. 5; it should be understood that the shape of[0041]mixer50 gradually transitions along axis F from a generally circular opening atinlet56 to a multifluted structure atoutlet58 to aide in the mixing. To provide contrasting views, FIGS. 3 and 4 illustratecenterbody39 in relation tomixer50, while FIG. 5 does not. Axis F is perpendicular to the view plane of FIG. 3 and is represented by cross hairs. Atoutlet58,passage54 terminates with acentral aperture60 surrounded by a number of lobes62 (only a few of which are specifically designated to preserve clarity) as best seen in FIG. 3.Aperture60 corresponds to a generally circular cross-section along axis F that is smaller in area than the circular cross-section along axis F at the circular opening ofinlet56.
• [0042]Lobes62 are radially disposed about axis F and gradually extend away from axis F with respect to a direction of travel along axis F frominlet56 tooutlet58. This direction is designated as “downstream” and the opposite direction along axis F is designated “upstream” in correspondence with the direction gas is discharged fromsystem40 throughdischarge36. Under this convention, a first position along axis F is downstream relative to a second position along axis F if the first position if farther along axis F in the downstream direction. Also, for this example, the second position is upstream relative to the first position because it is farther along axis F in the upstream direction.
• Each[0043]lobe62 is circumferentially positioned aboutpassage54 between a corresponding pair ofadjacent lobes62 to form aserpentine contour63 about axis F. Individually, each one oflobes62 is formed between two radii originating from axis F and intersecting points ofmixer50 that are relatively closest to axis F (minimum radius points) for the illustrated embodiment. In FIG. 3, arepresentative lobe62 is designated between the radial end points R1 and R2 each corresponding to a radius originating from axis F.
• As specifically designated for[0044]lobe62 between points R1 and R2 in FIG. 3,lobes62 each include a corresponding pair of confrontingwalls64 radially extending from axis F. Each pair of confrontingwalls64 are coupled by acurved dome66 to collectively form acorresponding ridge68 withradial apex70. Aslobes62 flare away from axis F in the downstream direction, a number oftroughs72 are formed, each gradually deepening between a corresponding adjacent pair oflobes62. Individually, each one oftroughs72 is formed between two radii originating from axis F and intersecting points ofmixer50 that are relatively farthest away form axis F (maximum radius points), which, for the illustrated embodiment, are coincident with theapices70 of the adjacent pair oflobes62. In FIG. 3, arepresentative trough72 is designated between the radial points R3 and R4. The shading dots in FIG. 2 schematically represent receding regions corresponding totroughs72.
• Each[0045]lobe62 includes aninner channel74 formed between the corresponding pair ofwalls64. Eachinner channel74 intersects the otherinner channels74 viapassage54 at a necked-down region75 as illustrated for the lobe between points R1 and R2. As eachlobe62 flares away from axis F in the downstream direction, inner channels diverge away from one another and axis F. Correspondingly,lobes62 each provide one of a number of divergent,inner chutes76 that open intopassage54 to direct exhaust flow EF as it passes throughmixer50.
• Each[0046]trough72 includes anouter channel84 formed betweenwalls64 ofadjacent lobes62. Eachouter channel84 is positioned between an adjacent pair ofinner channels74. Further,outer channels84 are arranged to alternate withinner channels74 about axis F. As eachtrough72 advances in the downstream direction along axis F,outer channels84 converge toward one another and axis F. Correspondingly,troughs72 each provide one of a number of convergentouter chutes86 to direct cooling fluid CF flowing betweenduct42 andconduit52 ofmixer50.
• It should be understood that[0047]walls64 are arranged to separateinner channels74 fromouter channels84 and correspondingly provide alternatinginner chutes76 andouter chutes86. Thus, with respect to a cross section along axis F taken atoutlet58,walls64 correspond to a number of annular sectors centered about axis F. Eachlobe62 andtrough72 belong to a different one of these sectors. In one preferred embodiment, these sectors each subtend an angle less than or equal to 90 degrees andlobes62 number at least 2. In a more preferred embodiment, these sectors each subtend an angle less than or equal to 45 degrees andlobes62 number at least 4. In a still more preferred embodiment, these sectors each subtend an angle of less than or equal to 30 degrees andlobes62 number at least 6. In a most preferred embodiment, these sectors each subtend an angle of less than or equal to 15 degrees andlobes62 number at least 12. In FIG. 3 , representative sectors S1 and S2 are illustrated corresponding to one oflobes62 and anadjacent trough72, respectively. Sectors S1 and S2 are defined by radii rs1, rs2, rs3.
• When traveling along axis F from[0048]inlet56 tooutlet58,lobes62 andtroughs72 gradually twist about axis F. Correspondingly,lobes62 andtroughs72 each have a curving spiral or helical shape about axis F. Also,inner channels74 andouter channels84 are turned about axis F, following a corresponding spiral or helical path. It should be understood that in the illustrated embodiment,lobes62,troughs72,inner channels74,outer channels84,inner chutes76, andouter chutes86 each follow a corresponding spiral path that rotates about axis F for less than a complete revolution. The twisted shape ofinner channels74 increases the line-of-sight blockage of hot parts ofengine32adjacent inlet56 throughoutlet58. The degree of twisting is preferably selected to provide a desired balance between the degree of blockage required and the cost/efficiency impact the twist may have, if any. For this illustrated embodiment, the shape oflobes62 turninner channels74 about axis F to block view ofinlet56 throughlobes62 from a line of sight parallel to axis F that originates downstream ofoutlet58.
• The amount of rotation may be expressed in units of degrees that a radius rotates about axis F as it traces one of these paths along axis F in the downstream direction. One representative path P extending from point TR[0049]1 to point TR2 is illustrated alongapex70 of acorresponding lobe62 in FIG. 5. In FIG. 5A, points TR1 and TR2 correspond to extreme positions of a radius tracing path P frominlet56 tooutlet58. Point TR1 corresponds to an end of path P atinlet56 and point TR2 corresponds to an end of path P atoutlet58. The angular separation between radii originating at axis F and terminating at points TR1 and TR2, respectively, is represented by angle A. Correspondingly, angle A also represents the amount of rotation of path P about axis F. In one preferred embodiment, angle A is at least 15 degrees. In a more preferred embodiment, angle A is at least 25 degrees. In a most preferred embodiment having twelve circumferentially spaced apartlobes62 andtroughs72 in a generally symmetric arrangement about axis F, angle A is about 27 to about 30 degrees. In other embodiments,mixer50 may be arranged to provide an amount of twist about axis F greater than 30 degrees for any oflobes62,troughs72,inner channels74,inner chutes76,outer channels84, and/orouter chutes86 up to and including one or more revolutions about axis F. Notably,mixer50 may utilize a counter-twist to minimize any efficiency losses that might arise and still provide the desired blockage.
• [0050]Mixer150 of another embodiment of the present invention is illustrated in the side, elevational view of FIG. 6; the end, elevational view of FIG. 7; and the top left, isometric view of FIG. 8.Mixer150 includesduct152 withpassage154 extending frominlet156 tooutlet158 in a manner analogous tomixer50. Furthermore,mixer150 can be interchanged withmixer50 in mixingsystem40 ofaircraft20 described in connection with FIGS.1-5.Mixer150 includeslobes162 each defined by a corresponding pair ofside walls164 radially extending from axis F and coupled together by acorresponding dome166 to form aridge168, examples of which are shown in FIGS. 6 and 8.Lobes162 are adjacently arranged to providetroughs172,inner channels174,inner chutes176,outer channels184, andouter chutes186 that turn about axis F in a manner analogous tomixer50. Furthermore,mixer150 utilizes a mixing technique analogous tomixer50. The shading dots in FIG. 6 schematically represent receding regions corresponding totroughs172.
• Each[0051]lobe162 includes awall portion194 extending from a first one of its corresponding pair ofwalls164 farther downstream along axis F than a second one of its corresponding pair ofwalls164 atoutlet158. Only a few ofwall portions194 are specifically designated to preserve clarity. It should be understood thatouter surface portion196 of eachwall portion194 follows the twisting path about axis F to cover a correspondinginner chute176 relative to a view plane downstream ofoutlet158, such as the view plane of FIG. 7. Becauseinner chute surface177 of eachinner chute176 is directly exposed to hot exhaust gas as it flows throughpassage154 frominlet156 tooutlet158,surface177 typically presents a more intense thermal signature thanouter surface portion196 of eachwall portion194 relative to this downstream view plane. Correspondingly, for each pair oflobe walls164,wall portion194 extending from one oflobe walls164 blocks theopposite lobe wall164 from a view along a line of sight parallel to axis F from a position downstream ofoutlet158.
• In some arrangements,[0052]wall portions194 may provide additional blockage of hot parts, such asturbine blades35 andcenterbody39 for the same degree of twist relative tomixer50. Furthermore,mixer150 withwall portions194 may be employed in situations where less twist is desired with comparable or greater thermal signature reduction. Referring back to FIG. 3, one alternative embodiment ofmixer150 may be provided through modification ofmixer50. For this adaptation, anoutlet region98 oflobes62 that has a hot inner surface visible throughoutlet158 is removed (only afew regions98 are illustrated to preserve clarity). Referring again to FIGS.6-8, the effect of this adaptation is to form aside wall slot198 in each lobe, leavingwall portion194 opposite theside wall slot198.
• [0053]Mixer250 of another embodiment of the present invention is illustrated in the side, elevational view of FIG. 9; the end, elevational view of FIG. 10; and the top left, isometric view of FIG. 11.Mixer250 includesduct252 withpassage254 extending frominlet256 tooutlet258 in a manner analogous tomixer150. Furthermore,mixer250 can be interchanged withmixer50,150 in mixingsystem40 ofaircraft20 as described in connection with FIGS.1-8.Mixer250 includeslobes262 each defined by a corresponding pair ofside walls264 radially extending from axis F and coupled together by acorresponding dome266 to form acorresponding ridge268, an example of which is specifically designated by reference numerals in FIG. 9.Lobes262 are adjacently arranged to providetroughs272,inner channels274,inner chutes276,outer channels284, andouter chutes286 that turn about axis F in a manner analogous tomixer50,150 (only a few of which are designated to preserve clarity). The shading dots in FIG. 9 schematically represent receding regions corresponding totroughs272.
• Each[0054]lobe262 includes awall portion294 extending a first one of its corresponding pair ofwalls264 farther downstream along axis F than a second one of its corresponding pair of walls atoutlet258. Only a few ofwall portions294 are specifically designated to preserve clarity. It should be understood thatouter surface portion296 of eachwall portion294 follows the twisting path about axis F to cover or hide a correspondinginner chute276 relative to a view plane downstream ofoutlet258, such as the view plane of FIG. 10 to reduce thermal signature as described in connection withmixer150.
• As in the case of[0055]wall portions194 ofmixer150,wall portions294 of mixer240 provide additional blockage of hot parts for the same degree of twist relative tomixer50. Furthermore,mixer250 withwall portions294 may be employed in situations where more blockage is desired with less twist relative tomixer50. Moreover,wall portions294 terminate in acurved end portion295 configured to turn working fluid as it exitsoutlet258. Only a few ofportions295 are specifically designated to preserve clarity. The curvature ofportions295 is preferably configured to turn at least a portion of the working fluid back towards axis F, providing for the recovery of at least some of the loss that might arise due to swirl caused by the mixing action. Correspondingly,wall portions294 each provide aregion297 that curves in a direction opposite the direction of the twist about axis F to provide acoanda surface298.
• [0056]Mixer350 of another embodiment of the present invention is illustrated in the end, elevational view of FIG. 12; the schematic partial sectional, end view of FIG. 13 withcenterbody39; and the top left, isometric view of FIG. 14 withcenterbody39.Mixer350 includesduct352 withpassage354 extending frominlet356 tooutlet358 in a manner analogous tomixers50,150,250. Furthermore,mixer350 can be interchanged withmixer50,150,250 in mixingsystem40 ofaircraft20 as described in connection with FIGS.1-11.Mixer350 includes the twisted lobe/trough structure ofmixer50 with like reference numerals representing like features. Specifically,mixer350 includeslobes62 each defined by a corresponding pair ofwalls64 radially extending from axis F and coupled together by a correspondingdome66 to form aridge68, an example of which is specifically designated by reference numerals in FIG. 12.Lobes62 are adjacently arranged to providetroughs72,inner channels74,inner chutes76,outer channels84, andouter chutes86 that turn about axis F in a manner analogous to mixer50 (only a few of which are shown to preserve clarity).
• [0057]Mixer350 includes a number of blockingfins392 that each extend intopassage354 along toward axis F along a different radius. Only a few offins392 may be specifically designated to preserve clarity. From the view plane of FIG. 12,fins392 form a spiral pattern about axis F (represented by cross hairs).Fins392 each emanate from aninner surface394 ofconduit352 at a minimum radiuspoint bounding outlet358, an example of which is designated as point MRP in the sectional view of FIG. 13. The schematic sectional view of FIG. 13 presents a sectional contour ofmixer350 along a plane perpendicular to and intersecting axis F betweeninlet356 andoutlet358 ofmixer350. Axis F is perpendicular to the view plane of FIG. 13 and is represented by cross hairs.
• The minimum radius point MRP generally coincides with the location where two[0058]adjacent lobes62 meet at the bottom of atrough72. Accordingly,fins392 each follow a spiral path of adifferent trough72, and each correspond to one oflobes62,inner channels74,inner chutes76,outer channels84 andouter chutes86. From the view plane of FIG. 12, the twisted path followed by eachfin392 provides further blockage of hot parts in addition to the obstruction caused by twistinginner channels74 and correspondinginner chutes76. It should be understood that in other embodiments, more orfewer fins392 may be utilized for the same number oflobes62 and/ortroughs72, or may be absent altogether.
• [0059]Mixer450 of another embodiment of the present invention is illustrated in the end, elevational view of FIG. 15; the schematic partial sectional, end view of FIG. 16 withcenterbody39; and the top left, isometric view of FIG. 17 withcenterbody39.Mixer450 includesduct452 withpassage454 extending frominlet456 tooutlet458 in a manner analogous tomixers50,150,250,350. Furthermore,mixer450 can be interchanged withmixer50,150,250,350 in mixingsystem40 ofaircraft20 as described in connection with FIGS.1-14.Mixer450 includes the twisted lobe/trough structure ofmixer50 with like reference numerals representing like features. Specifically,mixer450 includeslobes62 each defined by a corresponding pair ofwalls64 radially extending from axis F and coupled together by a correspondingdome66 to form aridge68, an example of which is specifically designated by reference numerals in FIG. 15.Lobes62 are adjacently arranged to providetroughs72,inner channels74,inner chutes76,outer channels84, andouter chutes86 that turn about axis F in a manner analogous to mixer50 (only a few of which are designated to preserve clarity).
• As in the case of[0060]mixer350,mixer450 includes a number of blockingfins492 that each extend intopassage454 toward axis F. Only a few offins492 may be specifically designated to preserve clarity. From the view plane of FIG. 15,fins492 form a spiral pattern about axis F (represented by cross hairs).Fins492 each emanate from aninner surface494 ofconduit452, and generally extending one of each pair ofwalls64 comprising alobe62. Collectively, thewall64 and the extendingfin492 are designatedextended wall portion464 as depicted in FIG. 16. It should be understood that the extension of eachfin492 intopassage454 is offset from the minimum radius point from whichfins392 emanate. This offset is best seen by comparing the sectional view of FIG. 13 formixer350 to the schematic sectional view of FIG. 16 formixer450, where the cross section of FIG. 16 corresponds to a sectional contour ofmixer450 along a plane perpendicular to and intersecting axis F at a position betweeninlet456 andoutlet458.Fins492 provide additional blockage of hot parts relative tomixer350 and follow a twisting path corresponding to the twist oflobes62,troughs72,inner channels74,inner chutes76,outer channels84, andouter chutes86. In alternative embodiments, the position offins492 relative to each other andcorresponding lobes62 and/ortroughs72 may be varied, may be intermixed withfins392, may vary in number relative to the number oflobes62 and/ortroughs72, or may be absent.
• [0061]Mixer550 of another embodiment of the present invention is illustrated in the end, elevational view of FIG. 18; the schematic partial sectional, end view of FIG. 19 withcenterbody39; and the top left, isometric view of FIG. 20 withcenterbody39.Mixer550 includesduct552 withpassage554 extending frominlet556 tooutlet558 in a manner analogous tomixer50,150,250,350,450. Furthermore,mixer550 can be interchanged withmixer50,150,250,350,450 in mixingsystem40 ofaircraft20 described in connection with FIGS.1-17.Mixer550 includeslobes562 each defined by a corresponding pair ofside walls564 radially extending from axis F and coupled together by acorresponding dome566 to form aridge568, an example of which is specifically designated by reference numerals in FIG. 18.Lobes562 are adjacently arranged to providetroughs572,inner channels574,inner chutes576,outer channels584, andouter chutes586 that turn about axis F in a manner analogous tomixer50,150,250,350,450.
• [0062]Mixer550 includes a number of hollow cooling fins in the form ofvanes592 that each extend intopassage554 toward axis F along a different radius. Only a few ofvanes592 may be specifically designated to preserve clarity. From the view plane of FIG. 18,vanes592 form a spiral pattern about axis F (represented by cross hairs).Vanes592 each emanate from aninner surface594 ofconduit552 at a minimum radiuspoint bounding outlet558, an example of which is designated as point MRP in the schematic sectional contour ofmixer550 shown in FIG. 19. The schematic sectional contour of FIG. 19 is taken along a plane perpendicular to and intersecting axis F betweeninlet556 andoutlet558 ofmixer550. Axis F is perpendicular to the view plane of FIG. 19 and is represented by cross hairs.
• The minimum radius point MRP generally coincides with the location where two[0063]adjacent lobes562 meet at the bottom of atrough572. Accordingly,vanes592 each follow a spiral path of adifferent trough572, and each correspond to one oflobes562,inner channels574,inner chutes576,outer channels584 andouter chutes586. From the view plane of FIG. 18, the twisted path followed by eachvane392 provides further blockage of hot parts in addition to the obstruction caused by twistinginner channels574 and correspondinginner chutes576.
• Each one of[0064]vanes592 defines apassageway593 therethrough. Eachpassageway593 has anopening595 intersecting a correspondingouter channel584 and anopening597intersecting plenum539 withincenterbody39 via plenum opening599 as best illustrated in FIG. 19. Accordingly,passageways593 provide fluid communication between each correspondingouter channel584 andplenum539.Vanes592 andcorresponding passageways593 are preferably configured to supply cooling fluid, such as air fromouter channels584 to coolcenterbody39 ofengine32 to suppress its thermal signature. In one embodiment, opening595 of eachpassageway593 is configured to capture the total (stagnation) pressure of the outer cooling fluid flowing though theouter channel584 it intersects. Typically this arrangement creates a cooling air driving potential for air originating from eachouter channel584 to pass into a respective one ofpassageways593 through itsopening595, and enterplenum539 throughcorresponding openings597 and599.Centerbody39 may also include one or more slits, slots, or other openings to vent cooling fluid fromplenum539 as appropriate (not shown). Notably in another embodiment, fewer than all ofvanes592 includepassageway593. In still other embodiments,vanes592 may be variously positioned relative to each other andlobes562 analogous tofins392,492, or may be absent altogether. In still other embodiments centerbody39 may lack aplenum539 and/oropenings599 or may be absent.
• The components of[0065]aircraft20, mixingsystem40 andmixers50,150,250,350,450,550 are preferably made from standard materials selected to perform as intended in the environment expected. For example,mixers50,150,250,350,450,550 may be made of a metallic material, a ceramic material, a composite material, or a combination of these selected to withstand expected exhaust temperatures. Furthermore, coatings may be applied to mixing system components according to the present invention to further suppress thermal signal and/or reduce radar cross section.
• Many further embodiments of the present invention are envisioned. For instance, in other embodiments, the features of any of[0066]mixers50,150,250,350,450, or550 may be combined, deleted, altered, duplicated or otherwise rearranged as would occur to those skilled in the art without departing from the spirit of the present invention. In other examples, the curved or twisting pattern in one or more ofmixers50,150,250,350,450,550, may have a different shape, such as a counter-twist, to offset any losses that might occur for a particular configuration. In still other embodiments, the twisted or curved lobes and/or troughs are absent, instead following a generally straight path with respect to axis F. Moreover, the size and shape of lobes, troughs, channels, chutes, wall portions, and fins may vary, may be nonuniformly distributed about axis F, and/or may not follow a uniform pattern of curvature or twist with respect to a reference axis. For example, only a portion of such features may be curved, two or more degrees of curvature or twist may be employed, different features may have different degrees of twist or curvature, and/or one or more of these features may be S-shaped. In another example, lobes of the present invention may not have a rounded, curvilinear shape, but rather have an angular or rectilinear shape. Further, a mixer according to the present invention may utilize lobes or troughs that twist or curve relative to a reference axis other than the centerline axis of the mixer. In other embodiments, fins and/or vanes may or may not be twisted or may follow a different twist or curvature pattern than lobes or troughs. In yet other embodiments, one or more other structures like fins343,443 and/or vanes543 may be utilized to the exclusion of twisted lobes and/or troughs to provide the requisite blockage. Also, wall portions, blocking fins and vanes ofmixers150,250,350,450,550 may be intermixed and/or positions of the structures varied with respect to the lobe/trough structure in a given mixer application. For instance, fins of both the side wall extending type and those emanating between side walls from a minimum radius point or otherwise can be utilized in the same mixer. In yet other embodiments of the present invention, variations and modifications as would otherwise occur to one skilled in the art are envisioned.
• In a further embodiment of the present invention, an exhaust mixer includes a passage extending from an inlet to an outlet to convey an exhaust flow therethrough. Several lobes are also included that are circumferentially disposed about the axis and that each define a corresponding one of several inner channels. These inner channels intersect one another between the inlet and the outlet. The lobes are each shaped to turn the inner channels about the axis to block viewing of the inlet through the lobes from a view plane perpendicular to the axis and downstream of the outlet.[0067]
• Still another embodiment includes a gas turbine engine and an exhaust mixer coupled to the engine along an outlet. This mixer includes several outward ridges radially projecting away from the axis that each define one of a number of inner channels intersecting at least one other of the inner channels within the mixer. These ridges are each shaped to turn the channels about the axis.[0068]
• In yet another embodiment, a gas turbine engine is included that is operable to produce an exhaust flow. Also included is a conduit coupled to the engine along an axis to mix the exhaust flow with cooling air. This conduit includes a number of lobes each defining a corresponding one of several inner channels circumferentially disposed about the passage. These lobes are each shaped to turn a corresponding one of the channels about the axis as they advance therealong. Also, a number of fins are included that each extend into the passage along the conduit and each converge with one or more other of the fins as the axis is approached.[0069]
• In a further alternative, an apparatus includes a gas turbine engine operable to produce an exhaust flow and a mixer coupled to the engine along an axis to mix the exhaust flow with cooling air. This mixer includes a passage positioned along the axis to convey the exhaust flow therethrough, several inner chutes circumferentially disposed about the passage, several outer chutes circumferentially disposed about the passage, and a number of vanes extending into the passage. The outer chutes are each positioned between a respective pair of inner chutes and the vanes each include a passageway in fluid communication with the corresponding one of the outer chutes.[0070]
• In a further alternative embodiment, an apparatus includes a gas turbine engine and a mixer coupled to the engine along an axis to mix cooling air with an exhaust flow produced during engine operation. This mixer includes an inlet and an outlet opposite the inlet along the axis and a number of lobes radially disposed about the axis. These lobes each turn about the axis between the inlet and outlet. The lobes include a number of wall portions at the outlet that each extend a first side of a respective one of the lobes past a second side of a respective one of the lobes along the axis to reduce thermal signature of the apparatus.[0071]
• In yet a further embodiment, a mixer is coupled to a gas turbine engine along an axis to mix cooling air with an exhaust flow produced during engine operation. This mixer includes an inlet and an outlet opposite the inlet along the axis, a number of inner chutes, and a number of wall portions at the outlet. The inner chutes are radially disposed about the axis and each turn about the axis as the inner chutes each extend therealong. The wall portions each extend from a corresponding one of the inner chutes to block the view of the corresponding one of the inner chutes from downstream of the outlet along a line of site parallel to the axis.[0072]
• In a still further embodiment, an apparatus includes a gas turbine engine and a mixer coupled to the engine along an axis to mix cooling air with an exhaust flow produced during engine operation. This mixer includes an inlet and an outlet opposite the inlet along the axis and a number of lobes radially disposed about the axis. The lobes each turn about the axis between the inlet and the outlet as the lobes each extend along this axis. The lobes each include a respective one of a number of first walls opposite a respective one of a number of second walls. The respective one of the first walls hides the respective one of the second walls from view along a line of site parallel to the axis that originates downstream of the outlet.[0073]
• All publications, patents, and patent applications cited herein are hereby incorporated by reference as if each individual publication, patent or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein including, but not limited to U.S. Pat. No. 4,576,002 to Mavrocostas; U.S. Pat. No. 4,566,270 to Ballard et al.; U.S. Pat. No. 4,548,034 to Maguire; U.S. Pat. No. 4,543,784 to Kirker; and 4,487,017 to Rodgers and U.S. Provisional Application No. 60/114,623 filed Jan. 4, 1999. While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes, modifications, and equivalents that come within the spirit of the invention as defined by the following claims are desired to be protected.[0074]

Claims (63)

What is claimed is:

1. An exhaust mixer, comprising:

a passage extending from an inlet to an outlet to convey an exhaust flow therethrough, said passage extending along a centerline axis of the mixer;

several lobes circumferentially disposed about the axis and each defining a corresponding one of several inner channels, said inner channels each intersecting at least one other of said inner channels between said inlet and said outlet; and

wherein said lobes are each shaped to turn said inner channels about said axis to block viewing of said inlet through said lobes from a view plane perpendicular to said axis and downstream of said outlet.

2. The exhaust mixer ofclaim 1, wherein inlet has a generally circular cross section along said axis and said outlet has a generally symmetric, serpentine contour about said axis.

3. The exhaust mixer ofclaim 1, wherein said mixer further includes several outer channels each positioned between a correspond pair of said inner channels, said lobes each include a different pair of a number of walls radially disposed about said axis, and said walls each separate a respective one of said inner channels from a respective one of said outer channels.

4. The exhaust mixer ofclaim 3, wherein said inner channels and said outer channels each correspond to a different one of a number of sectors of a cross section taken along said axis, said sectors each subtending an angle less than or equal to 45 degrees.

5. The exhaust mixer ofclaim 1, further comprising several fins each projecting into said passage from an inner surface bounding said inner channels or said passage.

6. The exhaust mixer ofclaim 5, wherein at least one of said fins is in the form of a vane defining a passageway in fluid communication with a corresponding one of said outer channels.

7. The exhaust mixer ofclaim 1, wherein said lobes each have a helical shape about said axis to rotate each of said inner channels at least 15 degrees about said axis, and said lobes each flare away from said axis as said lobes each advance in a direction from said inlet to toward said outlet along said axis.

8. The exhaust mixer ofclaim 1, wherein said lobes each include a pair of confronting walls with said corresponding one of said inner channels therebetween, a first one of said pair of confronting walls extending farther along said axis at said outlet than a second one of said pair of confronting walls for each of said lobes.

9. An apparatus, comprising:

a gas turbine engine; and

an exhaust mixer coupled to said engine along an axis, said mixer including several outward ridges radially projecting away from said axis, said ridges each defining one of a number of inner channels intersecting at least one other of said inner channels within said mixer, said ridges each being shaped to turn said inner channels about said axis.

10. The apparatus ofclaim 9, further comprising:

an aircraft, said engine being coupled to said aircraft and being configured to propel said aircraft; and

a duct coupled to said engine to expel a exhaust flow from said engine during engine operation, said mixer being positioned within said duct.

11. The apparatus ofclaim 9, wherein said mixer includes a passage extending from an inlet to receive said exhaust flow to an outlet to discharge said exhaust flow, said inner channels cooperate with said passage to direct the exhaust flow, said mixer defines a number of outer channels each provided between a corresponding pair of said ridges, and said outer channels are operable to direct cooling air to mix with the exhaust flow at said outlet when said engine is operating.

12. The apparatus ofclaim 9, wherein said inner channels each have a cross-sectional contour taken along said axis corresponding to an annular sector shape.

13. The apparatus ofclaim 9, further comprising a number of outer channels radially disposed about said axis, said outer channels each being positioned between a corresponding pair of said ridges, said ridges each including a different pair of a number of walls radially disposed about said axis, said walls each separating a respective one of said inner channels from a respective one of said outer channels.

14. The apparatus ofclaim 9, wherein said inner channels rotate about said axis at least 15 degrees as said ridges extend along said axis.

15. The apparatus ofclaim 9, further comprising a plurality of fins extending into said passage.

16. The apparatus ofclaim 9, wherein said ridges each include a pair of confronting walls with a corresponding one of said inner channels therebetween, a first one of said pair of confronting walls extending farther along said axis than a second one of said pair of confronting walls for each of said ridges.

17. The apparatus ofclaim 9, wherein said ridges are each have a helical shape about said axis to twist each of said inner channels at least about 20 degrees about said axis as said ridges extend along said axis, said ridges each include a different pair of a number of walls radially disposed about said axis, said walls each separate a respective one of said inner channels from a different one of a number of outer channels, said inner channels and said outer channels each correspond to a different one of a number of sectors of an imaginary circle with a center coincident with said axis, and said sectors each subtend an angle less than or equal to about 30 degrees.

18. An apparatus, comprising: an engine operable to discharge an exhaust flow and a mixer coupled to said engine along an axis to mix the exhaust flow with cooling air, said mixer including:

a passage extending from an inlet to an outlet along a centerline axis of said mixer; and

a number of inner chutes circumferentially disposed about said passage, said inner chutes each opening into said passage and being shaped to turn about said axis to block viewing of said engine through said inner chutes.

19. The apparatus ofclaim 18, wherein inlet has a generally circular cross section along said axis and said outlet has a generally symmetric, serpentine contour about said axis.

20. The apparatus ofclaim 18, wherein said mixer further includes several outer chutes each positioned between a correspond pair of said inner chutes.

21. The apparatus ofclaim 20, further comprising a several fins each projecting into said passage from an inner surface bounding said inner chutes or said passage.

22. The apparatus ofclaim 21, wherein one or more of said fins are in the form of a vane defining a passageway in fluid communication with a corresponding one of said outer channels.

23. The apparatus ofclaim 18, further comprising a number of wall portions each extending a corresponding one of said inner chutes to block said corresponding one of said inner chutes from view at a point downstream from said outlet along a line of sight parallel to said axis.

24. An apparatus, comprising:

a gas turbine engine operable to produce an exhaust flow;

a conduit coupled to said engine along an axis to mix the exhaust flow with cooling air, said conduit including a passage and a number of lobes each defining a corresponding one of several inner channels circumferentially disposed about said axis, said lobes each being shaped to turn a corresponding one of said inner channels about said axis as said corresponding one of said inner channels advances along said axis; and

a number of fins each extending into said passage from said conduit and converging with one or more other of said fins as said axis is approached.

25. The apparatus ofclaim 24, wherein said fins are each shaped to twist about said axis as said fins each extend along said axis.

26. The apparatus ofclaim 24, wherein said conduit defines a number of outer channels each positioned between a corresponding pair of said inner channels.

27. The apparatus ofclaim 26, wherein said passage includes an inlet to receive the exhaust flow and an outlet to discharge the exhaust flow, said outer channels turn about said axis with said inner channels, and said lobes each flare outward as said lobes each advance along said axis from said inlet to said outlet.

28. The apparatus ofclaim 24, wherein one or more of said fins each include a passageway in fluid communication with a corresponding one of said outer channels.

29. The apparatus ofclaim 28, wherein said engine includes a centerbody extending into said mixer through said inlet, and said passageway of each of said one or more fins is in fluid communication with an opening into said centerbody.

30. The apparatus ofclaim 24, wherein said inner channels twist about said axis to block view of said engine through said lobes from a view plane perpendicular to said axis, and downstream of said outlet and said fins are arranged in a spiral pattern at said outlet to at least partially block view through said passage from said view plane.

31. The apparatus ofclaim 24, further comprising an aircraft, said engine being coupled to said aircraft and being configured to propel said aircraft.

32. The apparatus ofclaim 24, wherein said lobes each include a different pair of a number of walls radially disposed about said axis, said walls each separate a respective one of said inner channels from a respective one of said outer channels, and a first one of said pair of confronting walls extends farther along said axis than a second one of said pair of confronting walls for each of said lobes.

33. The apparatus ofclaim 24, wherein said fins are visible through an outlet of said passage.

34. An apparatus, comprising: a gas turbine engine operable to produce an exhaust flow and a mixer coupled to said engine along an axis to mix the exhaust flow with cooling air, said mixer including:

a passage positioned along said axis to convey said exhaust flow therethrough;

several inner chutes circumferentially disposed about said passage;

several outer chutes circumferentially disposed about said passage, said outer chutes each being positioned between a respective pair of said inner chutes; and

a number of vanes each extending into said passage, one or more of said vanes each including a passageway in fluid communication with a corresponding one of said outer chutes.

35. The apparatus ofclaim 34, wherein said passage includes an inlet opposite said outlet along said axis, said inner chutes each turn about said axis as said inner chutes each extend along said axis, and said inner chutes each open into said passage.

36. The apparatus ofclaim 34, further comprising an aircraft, said engine being coupled to said aircraft and being configured to propel said aircraft.

37. The apparatus ofclaim 34, wherein said inner chutes are each defined by a corresponding one of a number of lobes radially disposed about said passage, said lobes each include a different pair of a number of walls radially disposed about said axis.

38. The apparatus ofclaim 37, wherein said vanes are radially disposed about said axis.

39. The apparatus ofclaim 37, wherein said lobes each have a helical shape rotating at least 15 degrees about said axis as said lobes each extend along said axis.

40. The apparatus ofclaim 34, wherein said engine includes a centerbody extending into said mixer, and said passageway of each of said one or more vanes is in fluid communication with a plenum in said centerbody.

41. An apparatus, comprising:

a gas turbine engine operable to produce an exhaust flow;

a conduit coupled to said engine along an axis to mix the exhaust flow with cooling air, said conduit including a passage and a number of lobes circumferentially disposed about said passage; and

a number of fins each extending into said passage from said conduit and being shaped to turn about said axis as said fins each advance along said axis.

42. The apparatus ofclaim 41, wherein said lobes each include a corresponding one of a number of inner channels.

43. The apparatus ofclaim 42, wherein said conduit defines a number of outer channels each positioned between a corresponding pair of said inner channels.

44. The apparatus ofclaim 42, wherein said lobes are each shaped to turn said inner channels with said fins at least 15 degrees about said axis.

45. The apparatus ofclaim 41 further comprising an aircraft, said engine being coupled to said aircraft and being configured to propel said aircraft.

46. The apparatus ofclaim 41, wherein said fins each extend radially relative to said axis and are visible through a discharge outlet of said passage.

47. An apparatus, comprising: a gas turbine engine and a mixer coupled to said engine along an axis to mix cooling air with an exhaust flow produced during engine operation, said mixer including:

an inlet and an outlet opposite said inlet along said axis;

a number of lobes radially disposed about said axis, said lobes each turning about said axis between said inlet and said outlet as said lobes each extend along said axis, said lobes including a number of wall portions at said outlet, said wall portions each extending a first side of a respective one of said lobes past a second side of said respective one of said lobes along said axis to reduce thermal signature of the apparatus.

48. The apparatus ofclaim 47, wherein said wall portions each at least partially obstruct view of an inner surface of said second one of said sides for said respective one of said lobes from a plane perpendicular to said axis and downstream from said outlet.

49. The apparatus ofclaim 47, wherein said wall portions are each shaped to define a coanda surface.

50. The apparatus ofclaim 47, wherein said wall portions each block view of said second side for said respective one of said lobes from a plane perpendicular to said axis and downstream from said outlet.

51. The apparatus ofclaim 47, wherein said lobes each include one of a number of inner channels radially disposed about said axis between said inlet and said outlet.

52. The apparatus ofclaim 51, wherein said mixer includes a number of outer channels each positioned between a corresponding pair of inner channels, said inner channels and said outer channels each twisting about said axis to block a line of sight view of said engine from said outlet through said inner channels.

53. The apparatus ofclaim 47, further comprising:

an aircraft, said engine being coupled to said aircraft and being configured to propel said aircraft; and

a duct coupled to said engine to discharge the exhaust flow from said engine during engine operation, said mixer being positioned within said duct.

54. An apparatus, comprising: a gas turbine engine and a mixer coupled to said engine along an axis to mix cooling air with an exhaust flow produced during engine operation, said mixer including:

an inlet and an outlet opposite said inlet along said axis;

a number of inner chutes radially disposed about said axis, said inner chutes each turning about said axis as said inner chutes each extend along said axis; and

a number of wall portions at said outlet, said wall portions each extending from a corresponding one of said inner chutes to block view of said corresponding one of said inner chutes from downstream of said outlet along a line of sight parallel to said axis.

55. The apparatus ofclaim 54, wherein said wall portions are each shaped to define a coanda surface.

56. The apparatus ofclaim 54, wherein said mixer includes a passage extending through said mixer from said inlet to said outlet, and said inner chutes each open into said passage between said inlet and said outlet.

57. The apparatus ofclaim 54, wherein said wall portions each cooperate with said corresponding one of said inner chutes to block view of said engine through said inner chutes.

58. The apparatus ofclaim 54, further comprising:

an aircraft, said engine being coupled to said aircraft and being configured to propel said aircraft; and

a duct coupled to said engine to discharge the exhaust flow from said engine during engine operation, said mixer being positioned within said duct.

59. An apparatus, comprising: a gas turbine engine and a mixer coupled to said engine along an axis to mix cooling air with an exhaust flow produced during engine operation, said mixer including:

an inlet and an outlet opposite said inlet along said axis;

a number of lobes radially disposed about said axis, said lobes each turning about said axis between said inlet and said outlet as said lobes each extend along said axis, said lobes each including a respective one of a number of first walls opposite a respective one a number of second walls, said respective one of said first walls hiding said respective one of said second walls from view along a view plane perpendicular to said axis and downstream of said outlet.

60. The apparatus ofclaim 59, wherein said first walls are each shaped to define a coanda surface.

61. The apparatus ofclaim 59, wherein said lobes each include one of a number of inner channels and said mixer includes a passage extending through said mixer from said inlet to said outlet.

62. The apparatus ofclaim 61, wherein said mixer includes a number of outer channels each positioned between a corresponding pair of inner channels, said inner channels and said outer channels each twisting about said axis to block a line of sight view of said engine from said outlet through said inner channels.

63. The apparatus ofclaim 59, further comprising:

an aircraft, said engine being coupled to said aircraft and being configured to propel said aircraft; and

a duct coupled to said engine to expel the exhaust flow from said engine during engine operation, said mixer being positioned within said duct.

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