USRE47304E1 - Nozzle arrangement and method of making the same - Google Patents

Abstract

A nozzle arrangement is disclosed herein for use with a supersonic jet engine that is configured to produce a plume of exhaust gases. The nozzle arrangement includes, but is not limited to, a nozzle having a trailing edge and a plug body partially positioned within the nozzle. The plug body has an expansion surface and a compression surface downstream of the expansion surface. A protruding portion of the plug body extends downstream of the trailing edge for a length greater than a conventional plug body length. The plug body is configured to shape the exhaust gases to flow substantially parallel to a free stream of air flowing off of the trailing edge of the nozzle and to cause the plume of exhaust gases to isentropically turn the free stream of air to move in a direction parallel to a longitudinal axis of the plug body.

Description

This application is a reissue application of U.S. patent application Ser. No. 13/541,495, filed 3 Jul. 2012 (now U.S. Pat. No. 9,121,369), which claims priority to previously filed U.S. Provisional Patent Application 61/525,604, filed Aug. 19, 2011, and entitled “Shaped Streamtube Nacelle For Reduced Sonic Boom Strength” which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention generally relates to aircraft and more particularly relates to nozzle arrangements and methods of making nozzle arrangements for use with supersonic jet engines.

BACKGROUND

Acoustic disturbances produced at supersonic flight speed by a propulsion system's nacelle cowling surface, along with those from the aerodynamic boundary surfaces of the inlet's captured stream tube and the jet plume exhaust from the nozzle, all influence the perceived loudness of an aircraft's sonic boom. A traditionally-designed nacelle produces numerous shocks that ultimately coalesce into the vehicle's overall sonic boom footprint. The challenge in attenuating the strength of these shock features lays in the inherent difficulty of rerouting flow streamlines in a supersonic flowfield without producing a discrete disturbance.

Spillage is an inlet characteristic that contributes strongly to sonic boom strength. Spillage is excess flow that is unusable by the propulsion system and naturally diverted (‘spilled’) around the sides of the intake through the inlet compression field. In a typical design, spillage occurs through the terminal shock, the only physical mechanism that can do so in a typical inlet design. The more spillage required, due for instance to off-design engine operation, the stronger the inlet's terminal shock automatically becomes, and the more detrimental the influence on sonic boom. Because it is a shock, this feature is discrete, overlaying an impulse into the vehicle's acoustic field. And because of its discrete nature, an impulse feature is difficult to attenuate or cancel using other low sonic-boom design techniques.

The angling of the cowling surface in the stream-wise direction at both the intake and nozzle exit contribute to sonic boom strength as does cowl blistering or bulging used to fit the nacelle around engine protuberances such as a gearbox. Intake cowl angle and nacelle bulging create blockage features to oncoming supersonic flow that generate compression shocks. In addition, the cowling angle at the nozzle exit, along with the downstream surfaces of any cowl bulging, produce expansion fans that tend to readapt to the local flowfield through compression shocks.

Finally, in a typical design, the exhaust jet plume itself aggravates the local acoustic field by generating strong compression shock and expansion-reshock features along its shear surface through flow-angle mismatch with the nacelle cowling and mal-adaption of the exhaust outflow pressure to the exit area of the nozzle. Off-design engine operation further aggravates this flow-angle and pressure mismatch. These issues are illustrated inFIGS. 1-3 which depict a conventional supersonic jet engine.

FIG. 1 schematically illustrates a prior artsupersonic jet engine20 having aninlet arrangement22 and anozzle arrangement24 configured for operation at a predetermined Mach speed.Inlet arrangement22 includes acowl26 and acenter body28.Center body28 is coaxially aligned withcowl26.Cowl26 includes acowl lip30 andcenter body28 includes acompression surface32 and an apex34 (also referred to as a “leading edge”).Cowl lip30 andcompression surface32 together define aninlet36 which admits air toturbo machinery38.

A protruding portion38 (also known as a “spike”) ofcenter body28 extends forward ofcowl lip30 by a distance L₁. A supersonic airflow (not shown) approaching prior artsupersonic jet engine20 will encounter protrudingportion38 prior to enteringinlet36. The supersonic flow will initially encounterapex34 resulting in an initial shock (not shown) that will extend in a rearward direction at an oblique angle that corresponds to, among other factors, the Mach speed at which prior artsupersonic jet engine20 is traveling. Conventionally, it is desirable to give protruding portion38 a length that will result in an initial shock that extends fromapex34 tocowl lip30 when the aircraft is moving at a predetermined Mach speed (also known as a “design speed” or a “cruise speed”). The length of a protruding portion that causes the initial shock to extend fromapex34 tocowl lip30 when the aircraft is moving at the predetermined Mach speed will be referred to herein as a “conventional spike length”.

Nozzle arrangement24 includes anozzle40 having atrailing edge42.Nozzle arrangement24 further includes aplug body44 having a surface.Trailing edge42 andsurface46 define anoutlet48.Plug body44 is configured to control the expansion of the exhaust gases (referred to herein as the “exhaust plume”) exhausted fromturbo machinery38 during operation of prior artsupersonic jet engine20. As the exhaust plume travels downstream alongplug body44,plug body44 has a continually decreasing diameter which provides space to accommodate the expanding gases of the exhaust plume. The ability ofplug body44 to control the expansion of exhaust gases of the exhaust plume ends at a trailingend50 ofplug body44. At a point downstream of trailingend50, the exhaust gasses of the exhaust plume will become fully expanded.

As illustrated inFIG. 1, a protrudingportion52 ofplug body44 extends beyondtrailing edge42 ofcowl40 by a distance L₂. As is known in the art, the length L₂is selected by engine designers to correspond with a point of intersection of Mach lines propagating off an internal surface oftrailing edge42 when the prior artsupersonic jet engine20 is operated at a power setting that corresponds with the predetermined Mach number. The length of a protruding portion that corresponds with the intersection point of the Mach lines propagating off of an internal surface oftrailing edge42 will be referred to herein as a “conventional plug body length”.

FIG. 2 illustrates a prior artsupersonic jet engine20 traveling at the predetermined Mach speed. As prior artsupersonic jet engine20 travels down range, afree stream52 of airapproaches protruding portion38. A portion offree stream52 has been illustrated in phantom lines as forming astream tube54.Stream tube54 has a diameter that corresponds with a diameter atcowl lip30 and has a length that corresponds with a discrete period of time of operation ofturbo machinery38. All of the air withinstream tube54 will have some interaction withinlet arrangement22—a portion of air withinstream tube54 will enterinlet36 and the remaining portion of air will be spilled out ofinlet36.

Interaction betweenfree stream52 andapex34 gives rise toinitial shock56. Interaction offree stream52 withcowl lip30 gives rise to aterminal shock58 that propagates inwardly towardscompression surface32. Interaction offree stream52 withcowl lip30 also gives rise to acowl shock60 that propagates outwardly from prior artsupersonic jet engine20. The strength ofcowl shock60 corresponds, in part, with the angle at whichcowl lip30 is canted with respect to the horizon. The greater the angle, the stronger will becowl shock60.

Prior artsupersonic jet engine20 is configured to consume air at a predetermined mass flow rate while traveling down range at the predetermined Mach speed. Assupersonic jet engine20 moves down range, it will consume a smaller volume of air than is available instream tube54. Accordingly, a portion of the air withinstream tube54 will enterinlet36 and a portion of the air withinstream tube54 will be spilled (“excess air”). The excess air withinstream tube54 must move in a direction that is radially outward with respect toinlet36 in order to spill. However, the excess air cannot move out of the way of the approachinginlet36 until after the excess air has passed throughterminal shock58. This is because the pressure disturbances arising out of the movement of the jet engine through the air towardsstream tube54 move only at the speed of sound while the jet engine approachesstream tube54 at speeds in excess of the speed of sound. Thus, the first opportunity for the excess air to move out of the way ofinlet36 does not occur until after the excess air has passed throughterminal shock58. This phenomenon is illustrated inFIG. 3

FIG. 3 illustrates anouter layer62 ofstream tube54 as it approachesinlet36.Outer layer62 represents the excess air, i.e., the portion ofstream tube54 that will not be consumed by turbo machinery38 (SeeFIG. 2) and therefore will not enterinlet36. Onceouter layer62 passes throughterminal shock58, it encounters the pressure disturbances associated with movement of priorart jet engine20 throughfree stream52.Outer layer62 is then pushed laterally aside and overflows aroundcowl lip30 as illustrated. This spilling ofouter layer62 out of the path ofinlet36 and aroundcowl lip30 causescowl shock60 to move forward ofcowl lip30, thereby increasing its strength. The stronger this shock is, the greater will be the noise disturbance associated with it.

Returning toFIG. 2, anexhaust plume63 is emitted fromoutlet48. In the illustrated example,exhaust plume63 comprises a straight cylinder of exhaust gas moving downstream away fromnozzle arrangement24. A free stream ofair64 approaching trailingedge42 ofnozzle40 is traveling at an angle with respect to the straight cylinder formed byexhaust plume63. As free stream ofair64passes trailing edge42 and encountersexhaust plume63, the shear layer created byexhaust plume63 behaves like a solid surface and causes free stream ofair64 to abruptly change direction. This abrupt change of direction gives rise to atail shock66. The encounter between free stream ofair64 andexhaust plume63 may cause the gases ofexhaust plume63 to also abruptly change direction, causing the plume to generate additional shocks downstream (not shown) The strength of tail shock66 (and the additional shocks in the plume) will depend upon the amount of misalignment betweenfree stream64 andexhaust plume63.

Asexhaust plume63 passes downstream of trailingend50,exhaust plume63 will quickly reach a fully expanded condition. Starting from the point whereexhaust plume63 is fully expanded and moving downstream,exhaust plume63 andfree stream64 will flow parallel to one another and both will flow in a direction that is parallel to a longitudinal axis ofplug body44. The transitional region, which starts wherefree stream64 initially encountersexhaust plume63 and which ends whereexhaust plume63 andfree stream64 flow parallel to a longitudinal axis ofplug body44, can give rise to expansions and compressions that, due to their proximity totail shock66, may contribute to the perceived loudness of sonic boom resulting from movement of prior artsupersonic jet engine20 at the predetermined Mach speed.

Accordingly, it is desirable to provide an inlet arrangement that is configured to mitigate the concerns described above. In addition, it is desirable to provide a method for assembling such an inlet arrangement. Furthermore, other desirable features and characteristics will become apparent from the subsequent summary and detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

A nozzle arrangement and a method of making a nozzle arrangement for use with a supersonic jet engine configured to provide a plume of exhaust gases when the engine is operating at a predetermined power setting and moving at a predetermined Mach speed is disclosed herein.

In a first, non-limiting embodiment, the nozzle arrangement includes, but is not limited to a nozzle that is configured to exhaust the plume of exhaust gases. The nozzle has a trailing edge that is oriented at a predetermined angle with respect to an axial direction of the nozzle. The nozzle arrangement further includes a plug body that is partially positioned within the nozzle and that is coaxially aligned with the nozzle. The plug body has an expansion surface and a compression surface downstream of the expansion surface. A protruding portion of the plug body extends downstream of the trailing edge for a length greater than a conventional plug body length. The protruding portion of the plug body has a substantially circular cross section along substantially an entire longitudinal length of the protruding portion of the plug body. The plug body is configured to shape the plume of exhaust gases such that the plume of exhaust gases flows substantially parallel to a direction of a free stream of air flowing off of the trailing edge of the nozzle proximate the trailing edge of the nozzle and further configured to cause the plume of exhaust gases to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle at a location downstream of the trailing edge of the nozzle such that the free stream of air flowing off of the trailing edge moves in a direction parallel to a longitudinal axis of the plug body.

In another non-limiting embodiment, the nozzle arrangement includes, but is not limited to, a nozzle that is configured to produce the plume of exhaust gases. The nozzle has a trailing edge that is oriented at a predetermined angle with respect to an axial direction of the nozzle. The nozzle arrangement further includes a plug body that is partially positioned within the nozzle and coaxially aligned with the nozzle. The nozzle arrangement further includes, but is not limited to, a bypass wall disposed between the nozzle and the plug configured to direct a bypass airflow out of the nozzle. The plug body has an expansion surface and a compression surface downstream of the expansion surface. A protruding portion of the plug body extends downstream of the trailing edge for a length greater than a conventional plug body length. The protruding portion of the plug body has a substantially circular cross section along substantially an entire longitudinal length of the protruding portion of the plug body. The plug body is configured to shape the plume of exhaust gases and the bypass airflow such that the plume of exhaust gases and the bypass air flow substantially parallel to a direction of a free stream of air flowing off of the trailing edge of the nozzle proximate the trailing edge of the nozzle and further configured to cause the plume of exhaust gases and the bypass airflow to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle at a location downstream of the trailing edge of the nozzle such that the free stream of air flowing off of the trailing edge moves in a direction parallel to a longitudinal axis of the plug body.

In a third non-limiting embodiment, the method includes, but is not limited to the step of providing a nozzle and a plug body. The nozzle is configured to exhaust the plume of exhaust gases. The nozzle has a trailing edge that is oriented at a predetermined angle with respect to an axial direction of the nozzle. The plug body has an expansion surface and a compression surface downstream of the expansion surface. The method further includes, but is not limited to, positioning the plug body with respect to the nozzle such that the plug body is partially positioned within the nozzle and coaxially aligned therewith and such that a protruding portion of the plug body extends downstream of the trailing edge for a length greater than a conventional plug body length. The protruding portion of the plug body has a substantially circular cross-section along substantially an entire longitudinal length of the protruding portion of the plug body. The plug body is configured to shape the plume of exhaust gases such that the plume of exhaust gases flows substantially parallel to direction of the free stream of air flowing off of the trailing edge of the nozzle proximate the trailing edge of the nozzle. The plug body is further configured to cause the plume of exhaust gases to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle at a location downstream of the trailing edge of the nozzle such that the free stream of air flowing off of the trailing edge moves in a direction parallel to a longitudinal axis of the plug body.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and

FIG. 1 is a schematic view illustrating a prior art jet engine;

FIG. 2 is a schematic view illustrating the prior art jet engine ofFIG. 1 moving through a free stream at a predetermined Mach number;

FIG. 3 is an expanded view of a portion of the prior art jet engine ofFIG. 2 illustrating the spillage of air around a cowl lip of an inlet;

FIG. 4 is a schematic view illustrating a portion of a jet engine and depicting the air that the jet engine will consume and the fully expanded exhaust plume that the jet engine will produce;

FIG. 5 is a schematic view illustrating an embodiment of a jet engine having an inlet arrangement and a nozzle arrangement made in accordance with the teachings of the present disclosure;

FIG. 6 is an axial view of the inlet arrangement ofFIG. 5;

FIG. 7 is an axial view of the nozzle arrangement ofFIG. 5;

FIG. 8 is a schematic view of the jet engine ofFIG. 5 traveling through a free stream at a predetermined Mach speed;

FIG. 9 is an expanded view of a portion of the inlet arrangement ofFIG. 5;

FIG. 10 is a schematic view of the jet engine ofFIG. 5 illustrating a technique for designing the plug body of the nozzle arrangement;

FIG. 11 is a flow diagram illustrating an embodiment of a method for making an inlet arrangement in accordance with the teachings of the present disclosure; and

FIG. 12 is a flow diagram illustrating an embodiment of a method for making a nozzle arrangement in accordance with the teachings of the present disclosure.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

An inlet arrangement is disclosed herein that substantially eliminates the spillage of excess air from a stream tube when the stream tube encounters a supersonic jet engine inlet moving at supersonic speeds. In an embodiment, the inlet arrangement includes a lengthened center body having an extended protruding portion that pre-spills the air from the stream tube before the stream tube encounters the inlet and/or the terminal shock. The length of the center body is increased such that length L₁(seeFIG. 1) exceeds a conventional spike length. In addition, the protruding portion has contours and is dimensioned so as to cause substantially all of the excess air to be pushed out of the path of the approaching inlet as the stream tube passes over the protruding portion. As a result, the air of the stream tube that remains in the path of the inlet will have a mass flow rate that matches the consumption rate of the turbo machinery of the jet engine when the jet engine is moving at a predetermined Mach speed and operating at a predetermined power setting. This substantially eliminates spillage at the inlet and permits the cowl shock to rest substantially directly on the cowl lip. This greatly diminishes the strength of the cowl shock and, as a result, diminishes the perceived noise associated with the cowl shock.

Additionally, in accordance with at least one embodiment, the inlet arrangement disclosed herein permits the cowl to have a substantially lower cowl angle as compared with conventional inlet arrangements. Although lowering the cowl angle will cause the inlet to have a larger diameter, by dimensioning and configuring the protruding portion appropriately, the stream tube approaching the inlet can be lofted to whatever height is necessary to meet the increased diameter of the inlet. Furthermore, because of the extended length of the protruding portion, the stream tube approaching the inlet can not only be lofted, but can also be turned to align more closely with a longitudinal axis of the center body to more closely align with the lower cowl angle. The reduced cowl angle will further diminish the strength of the cowl shock and, in turn, reduce the perceived noise associated with the cowl shock.

A nozzle arrangement is disclosed herein that substantially eliminates the misalignment between the free stream of air flowing past the trailing edge of the nozzle and the exhaust plume. In accordance with one embodiment, the nozzle arrangement includes a lengthened plug body having an extended protruding portion such that the length L₂(seeFIG. 1) exceeds the conventional plug body length. Furthermore, the plug body has an isentropic compression surface and is configured to cause the exhaust plume to exit the nozzle in a direction that is substantially aligned with the direction of the free stream of air flowing past the trailing edge of the nozzle. Such alignment will reduce or eliminate the shock that would otherwise form from a sudden change in direction of the free stream when encountering a misaligned exhaust plume.

Furthermore, in accordance with a further embodiment, by lengthening L₂, the full expansion of exhaust plume gases can be delayed until the jet engine has moved further down range as compared with a conventional jet engine having a conventional plug body. This extends the transitional phase of the exhaust plume and provides an opportunity to isentropically turn the free stream to a direction parallel to a longitudinal axis of the jet engine, thereby eliminating any shock that might otherwise be provoked by such a change of direction of the free stream. In yet another embodiment, the plug body can further be configured to permit the trailing edge of the nozzle to have a reduced angle as compared with the angle of the trailing edge of a nozzle on a conventional jet engine.

As set forth above, both the inlet arrangement and the nozzle arrangement disclosed herein permit their respective cowl lip and nozzle trailing edge to have relatively shallow angles with respect to a free stream of air as compared with the cowl lip and nozzle trailing edge of a conventional inlet arrangement and nozzle arrangement. The shallowness of these angles substantially reduces the cross-sectional profile of the inlet arrangement and nozzle arrangement with respect to the free stream during supersonic flight. Consequently, the inlet arrangement and the nozzle arrangement of the present disclosure each greatly diminish the drag acting on a supersonic jet engine equipped with either or both the inlet arrangement and the nozzle arrangement disclosed herein.

A greater understanding of the solutions described above and of the method for implementing these solutions may be obtained through a review of the illustrations accompanying this application together with a review of the detailed description that follows.

FIG. 4 is a schematic view illustrating a genericsupersonic jet engine70 having aninlet72 and anozzle74. For simplification, genericsupersonic jet engine70 has been drawn without a center body disposed ininlet72 and without a plug body disposed innozzle74. Genericsupersonic jet engine70 includesturbo machinery76 configured to consume air at a predetermined rate and to produce exhaust gases at a predetermined rate and pressure whileturbo machinery76 is operating at a predetermined power setting and moving at a predetermined speed.

Astream tube78 is positioned ahead of genericsupersonic jet engine70.Stream tube78 has a diameter that corresponds to the diameter ofinlet72 and represents the air in the free stream that lies on a path that will be taken byinlet72 as genericsupersonic jet engine70 travels upstream. Accordingly, all of the air included instream tube78 will interact in some way withinlet72. Some of that air will pass throughinlet72 while the remaining air will spill over the cowl lip ofinlet72 becauseturbo machinery76 cannot consume it.

A remainingstream tube80 is illustrated withinstream tube78. Remainingstream tube80 represents the air withinstream tube78 that will be consumed byturbo machinery76 of genericsupersonic jet engine70. All air withinstream tube78 other than remainingstream tube80 will spill around the cowl lip ofinlet72 whenstream tube78encounters inlet72. One goal of the inlet arrangement of the present disclosure is to push all air other than the air contained within remainingstream tube80 out of the path ofinlet72 beforestream tube78encounters inlet72.

Anexhaust plume82 is positioned downstream of genericsupersonic jet engine70.Exhaust plume82 represents the volume of gases that will be exhausted byturbo machinery76 when genericsupersonic jet engine70 is operated at a predetermined power setting and is moving at a predetermined speed. As illustrated,exhaust plume82 has a diameter that is smaller than the diameter of thenozzle74. However, when the exhaust gases exitnozzle74, their outer periphery will have a diameter equal to the diameter ofnozzle74. After the exhaust gasses move downstream and are free of the influence of a plug body, their diameter will shrink until the exhaust gases are fully expanded and their static pressure has equalized with the static pressure of the free stream surroundingexhaust plume82. One goal of the nozzle arrangement of the present disclosure is to ensure that the free stream air flowing past an external portion ofnozzle74 changes direction isentropically (i.e., without shocks) as it coalesces with a fully expandedexhaust plume82.

FIG. 5 is a schematic view illustrating asupersonic jet engine90 including aninlet arrangement92 and anozzle arrangement94 made in accordance with the teachings of the present disclosure.Supersonic jet engine90 further includesturbo machinery96 which is configured to consume air at a predetermined rate and to exhaust gases at a predetermined rate and pressure whensupersonic jet engine90 is moving at a predetermined speed and operating at a predetermined power setting. It should be understood that althoughinlet arrangement92 is depicted as having an axisymmetric inlet configuration, in other embodiments, other configurations are possible.

Inlet arrangement92 includes acowl98 having acowl lip100, and acenter body102 positioned at least partially withincowl98 and coaxially aligned therewith.Center body102 includes a protrudingportion104 having a length that exceeds a conventional spike length. For comparison purposes, a protrudingportion106 having a conventional spike length has been illustrated in phantom and overlaid on top ofcenter body102. The length of protrudingportion104 will correspond with the desired use and/or specifications forsupersonic jet engine90 and may be determined based on a number of factors including, but not limited to, the smoothness characteristics of the streamtube required to meet a desired sonic boom loudness metric, and the amount of on-design pre-shock spillage required to match and hold the inlet to low post-shock spillage at off-design conditions.

Center body102 is an exemplary center body that is compatible with the teachings of the present disclosure and includes an apex108, aninitial compression surface110, anexpansion surface112, and afinal compression surface114. In other embodiments,center body102 may omit an intermediate expansion surface (expansion surface112).Cowl lip100 is spaced apart fromfinal compression surface114 to define aninlet116 through which air may pass for consumption/use byturbo machinery96. As illustrated,apex108 is positioned well upstream ofinlet116 and consequently can have an impact on a stream tube approachingsupersonic jet engine90 well before that stream tube encountersinlet116.

When a stream tube encountersapex108, the air of the stream tube will be diverted in a direction radially outwardly fromcenter body102. As a result of this outward movement, a portion of the diverted air will be moved out of the pathway ofinlet116. Because protrudingportion104 has a diameter that increases in the downstream direction, as the stream tube continues to move towardsinlet116, an increasing amount of air will be diverted out of the pathway ofinlet116. Method of Characteristics may be used to determine the contour ofcenter body102. Method of Characteristics is well known in the art and uses classical gas dynamic relationships and equation marching methods for rapid preliminary analysis of promising supersonic shapes and bodies. Using Method Of Characteristics, the precise contour and dimensions ofcenter body102 and of protrudingportion104 can be selected such that the air of the stream tube that remains in the pathway ofinlet116 will substantially match the predetermined rate of air consumption byturbo machinery96. As a result, substantially all of the remaining air that passes through the terminal shock will be consumed byturbo machinery96 and substantially no spillover of air will occur atcowl lip100. When using Method of Characteristics to generate an appropriate surface configuration, a desired surface curve is first selected for the captured streamtube that defines a continuously smooth, isentropic lofting of the streamtube surface into the intake's cowl lip. Method of characteristics is then used to design the curvature of the protrudingsurface104 of the centerbody that produces the supersonic compression and expansion field that results in the desired streamtube shape (i.e. an ‘inverse design’ approach). Additional important parameters that method of characteristics uses in this instance include freestream Mach number, level of relaxed isentropic compression desired, and Mach number distribution along the terminal shock. Using this information, Method Of Characteristics could be used to generate an appropriate surface geometry forcenter body102.

To ensure that the divergence of air byinitial compression surface110 does not generate a shock, in some embodiments,initial compression surface110 may be configured to be an isentropic compression surface. As is known in the art, isentropic compression surfaces have a continuously curved shape that is devoid of any discrete discontinuities that would otherwise give rise to discrete shocks. Once the air of the stream tube has been diverted byinitial compression surface110, it may be desirable to turn the stream tube back in a direction more aligned with a longitudinal axis ofsupersonic jet engine90. This is accomplished byexpansion surface112 which, due to its curvature, causes the stream tube to turn back in an axial direction. This allowscowl lip100 to have a very shallow angle with respect to the local free stream which, in turn, substantially reduces the strength of the cowl shock generated bycowl lip100.

Final compression surface114 serves the same purpose served by conventional compression surfaces of conventional supersonic jet engines, i.e., reducing the speed of the oncoming stream tube before the stream tube encounters the terminal shock and before the stream tube enters the inlet. As known in the art, a supersonic airflow can be slowed using a curved surface to turn the direction of the airflow. Again, it is desirable to avoid generating any shocks during this final compression stage. Accordingly, in some embodiments, an isentropic compression surface may be used. In other embodiments, it may be desirable to configurefinal compression surface114 to have a relaxed isentropic compression configuration. A relaxed isentropic compression surface is known in the art and is disclosed and described in pending U.S. patent application Ser. Nos. 11/639,339; 13/338,005; and 13/338,010, each of which is hereby incorporated herein by reference in their entirety. By configuringfinal compression surface114 to have a relaxed isentropic compression configuration, theairflow approaching inlet116 will undergo a reduced amount of turning from the axial direction ofsupersonic jet engine90 as compared with the amount of turning caused by a traditional isentropic compression surface. This contributes tocowl lip100 having a relatively small angle with respect to the axial direction ofsupersonic jet engine90, and thus contributes to a reduction in the strength of any resulting cowl shock.

Supersonic jet engine90 further includes abypass118.Bypass118 is an alternate flow pathway throughsupersonic jet engine90 that is commonly used to route turbulent air having relatively high pressure distortions around andpast turbo machinery96 rather than permitting such turbulent air to pass throughturbo machinery96. A bypass, such asbypass118, further contributes tocowl lip100 having a relatively shallow angle with respect to a longitudinal axis ofsupersonic jet engine90. This, in turn, further reduces the strength of the cowl shock formed bycowl lip100. The use of the bypass in a supersonic jet engine is known in the art. For example, a bypass is disclosed and described in U.S.Provisional Patent Application 60/960,986 and also in U.S. patent application Ser. No. 12/000,066, each of which are hereby Incorporated herein by reference in their entirety.

Inlet arrangement92 includes abypass splitter120.Bypass splitter120 is a physical structure which divides (splits) theair entering inlet116, causing a portion of the air to travel alongbypass118 and causing another portion of the air to follow apath122 that leads toturbo machinery96.Turbo machinery96 will pass through multiple power settings as the aircraft accelerates to the pre-determined Mach speed. At each power setting,turbo machinery96 will consume air at a corresponding mass flow rate which will differ from the predetermined mass flow rate at the predetermined Mach speed. As set forth above,center body102 and protrudingportion104 are configured to pre-spill an amount of air that will cause the amount ofair entering inlet116 to substantially match the mass flow rate at the predetermined Mach speed and the predetermined power setting. To the extent that there is any mismatch between theair entering inlet116 and the air that will be consumed byturbo machinery96 when operating at the predetermined power setting and moving at the predetermined Mach speed and to the extent that such mismatch leads to spillage, that spillage will occur overbypass splitter120, not cowllip100. Spillage overbypass splitter120 will not impact the strength of the cowl shock. For other Mach speeds and for other power settings, the rate ofair entering inlet116 may not match the rate at whichturbo machinery96 consumes air. For those Mach speeds and power settings, the excess air that entersinlet116 will spill overbypass splitter120 and intobypass118. In this manner, bypass118 serves as an overflow pathway for air that cannot be consumed byturbo machinery96.

Nozzle arrangement94 includes anozzle124 having a trailingedge126, and aplug body128 that is positioned at least partially within thenozzle124 and coaxially aligned therewith.Plug body128 includes a protrudingportion130 having a length that exceeds a conventional plug body length. For comparison purposes, a protrudingportion132 having a conventional plug body length has been illustrated in phantom and overlaid on top ofplug body128. The length of protrudingportion130 will correspond with the desired use and/or specifications forsupersonic jet engine90 and may be determined based on a number of factors including, but not limited to, the smoothness characteristic of the streamtube required to meet a desired sonic boom loudness metric, the jet exit pressure and Mach number, and the maximum practical length from a design standpoint.

Plug body128 includes a trailingend134, anexpansion surface136 and acompression surface138. As illustrated in the embodiment presented in FIG. 5,compression surface 138 has a concave configuration. See also, FIGS. 8 and 10.Expansion surface136 is spaced apart from trailingedge126 to define anoutlet140 through which exhaust gases pass and are formed into an exhaust plume. The exhaust gases are produced byturbo machinery96 at a predetermined mass flow rate whenturbo machinery96 is operated at a predetermined power setting. Consequently, the size and shape ofoutlet140 can be configured to obtain a desired amount of thrust.

The exhaust plume expelled fromnozzle124 will have a predetermined static pressure that corresponds with the exit area ofoutlet140 and that further corresponds with the mass flow rate of the exhaust gases flowing out ofturbo machinery96 whenturbo machinery96 is operating at the predetermined power setting and whensupersonic jet engine90 is moving at the predetermined Mach speed. Trailingedge126 has a smaller angle with respect to an axial direction ofsupersonic jet engine90 as compared with a traditional nozzle on a conventional supersonic jet engine. The smaller trailing edge angle gives rise to less drag as the free stream flows over an outer surface of thenozzle124 and causes the free stream to have a shallower angle as it flows past trailingedge126.

The presence ofbypass118 contributes tonozzle124 having a very shallow angle with respect to an axial direction ofsupersonic jet engine90. To accommodate the presence ofbypass118,nozzle arrangement94 includesbypass wall141. Air flowing throughbypass118 will flowpast bypass wall141 and will join together with the exhaust gases expelled byturbo machinery96 to form the exhaust plume. Despite the illustration inFIG. 5 of an embodiment of a supersonic jet engine that includes a bypass, it should be understood that the teachings disclosed herein are compatible with supersonic jet engines that do not include a bypass.

As will be discussed below,nozzle124 has an annular configuration. Consequently, the exhaust plume emitted fromnozzle124 also has an annular configuration.Nozzle arrangement94 enables the exhaust plume to remain in an annular configuration for a longer distance than a conventional nozzle arrangement would because protrudingportion130 has a length that exceeds a conventional plug body length. Accordingly, plugbody128 is configured to enable the exhaust plume to remain in an annular configuration (albeit a shrinking annular configuration) as it moves in a downstream direction rather than immediately collapsing down to the fully expanded exhaust plume depicted inFIG. 4. By extending the distance over which the exhaust plume remains in an annular configuration, the distance over which the free stream turns to align with a longitudinal axis ofsupersonic jet engine90 is extended. This helps to prevent a shock from forming.

By providing aplug body128 with a protrudingportion130 that exceeds a conventional plug body length, the shape and contour of the annular exhaust plume can be controlled well after it has been expelled fromnozzle124 and it can be conformed to flow tangentially with the free stream moving past trailingedge126. By configuringplug body128 to have a surface geometry that causes the exhaust plume to have a static pressure that is substantially equal to the static pressure of the free stream flowing past trailingedge126, plugbody128 can control the rate at which the free stream turns towards an axial direction ofsupersonic jet engine90. As will be discussed below, the contour and configuration ofplug body128 and protrudingportion130 can be determined using Method of Characteristics.

FIG. 6 illustrates an axial view ofinlet arrangement92 in accordance with one embodiment. As illustrated,inlet arrangement92 has an axisymmetric configuration.Apex108 is positioned on a longitudinal axis ofsupersonic jet engine90.Center body102 is coaxially aligned on the same longitudinal axis and withbypass splitter120 which, in turn, is coaxially aligned with thecowl lip100. In other embodiments,inlet arrangement92 need not be axisymmetric but may have other configurations.

FIG. 7 illustrates an axial view of thenozzle arrangement94 in accordance with one embodiment. As illustrated,nozzle arrangement94 has an axisymmetric configuration. Trailingend134 is positioned on a longitudinal axis ofsupersonic jet engine90.Plug body128 is coaxially aligned withbypass wall141 which, in turn, is coaxially aligned with trailingedge126.

FIG. 8 is a schematic view illustratingsupersonic jet engine90 while traveling at the predetermined Mach speed and whileturbo machinery96 is operating at the predetermined power setting. Acowl shock142 and aterminal shock144 are illustrated propagating outwardly and inwardly, respectively, fromcowl lip100.Stream tube78 is positioned upstream ofsupersonic jet engine90 and has a diameter equal to the diameter ofinlet116. Remainingstream tube80 is illustrated withinstream tube78 and represents the volume of air that will be consumed byturbo machinery96.

Whenstream tube78encounters apex108, the air ofstream tube78 begins to divert in a radially outward direction. This movement will push a portion of the air ofstream tube78 out of the path ofinlet116. Asstream tube78 continues to move towardsinlet116, the air ofstream tube78 is continuously pushed in a radially outward direction by the surface ofcenter body102 which has an increasing diameter in the downstream direction. The movement of the excess air ofstream tube78 out of the path ofinlet116 is depicted byarrow143. The radial expansion of the outer diameter of remainingstream tube80 is depicted byarrow145. By the time that remainingstream tube80 travels from the position initially shown inFIG. 8 to a position immediately upstream ofinlet116, the outer diameter of remainingstream tube80 has expanded such that it is equal to the diameter ofinlet116.

Because of the contour and dimensions ofcenter body102 and, in particular, the contour and dimensions of protruding portion104 (seeFIG. 5), the volume of air of remainingstream tube80 is substantially equal to the rate at whichturbo machinery96 consumes air over a predetermined period of time. As a result, substantially all of the air of remainingstream tube80 will enterinlet116 and will be consumed byturbo machinery96 after passing throughterminal shock144. This enablesterminal shock144 to remain attached tocowl lip100. Furthermore,center body102 is configured to control and direct the flow of air of remainingstream tube80 such that the flow of air entersinlet116 at a very shallow angle as compared with the angle at which the flow of air enters a conventional supersonic jet engine. This allowscowl lip100 to have a relatively shallow angle and, consequently, a relatively weak cowl shock.

Atnozzle124, exhaust gases are expelled fromoutlet140 at a predetermined mass flow rate and static pressure that is determined, in part, by the area and shape ofoutlet140 and also by the rate and pressure at whichturbo machinery96 expels gas. As the exhaust gases move past trailingedge126, they are no longer constrained by the walls of thenozzle124. Accordingly, the natural tendency of the exhaust gases would be to expand outwardly in a direction transverse to the downstream direction as they move in the downstream direction. Movement of the exhaust gases in the direction transverse to the downstream direction is opposed by the static pressure of the free stream flowing past trailingedge126. Similarly, movement of the free stream moving past trailingedge126 in the direction transverse to the downstream direction is opposed by the static pressure of the exhaust gases. Consequently, at the point where the free stream and the exhaust gases move past trailingedge126, they will encounter and oppose one another. If one flow has a greater static pressure than the other, then both flows will turn towards the flow having the weaker static pressure.

Nozzle arrangement94 is configured such that the exhaust gases will have a static pressure that matches the local free stream at the nozzle exit. Because of this and because of the contour and configuration ofplug body128, the two flows will not turn in the direction of the free stream. Atoutlet140, plugbody128 has a contour that presents an expansion surface (expansion surface136, seeFIG. 5) to the exhaust gases, allowing the exhaust gases to expand in a direction away from the free stream. By selecting a particular contour and configuration forplug body128 and protruding portion130 (seeFIG. 5), the exhaust gases can be allowed to expand radially inwardly at a rate that allows their outer periphery to provide an appropriate amount of static pressure to the free stream such that the free stream and the exhaust gases will flow tangentially to one another at their shear surface without either flow experiencing an immediate change in direction.

As the exhaust gases continue to move in a downstream direction away fromoutlet140, they continue to expand in a radially inward direction and are permitted to do so by the diminishing diameter of protruding portion130 (seeFIG. 5). At some point along the surface ofplug body128, the exhaust gases will move off of expansion surface136 (seeFIG. 5) and onto compression surface138 (seeFIG. 5). Now faced with a compression surface, the exhaust gases will have a diminished ability to expand in a radially inward direction and, consequently, the exhaust gases will begin to return to an axially aligned flow. By giving protruding portion130 (seeFIG. 5) an appropriate contour and configuration, protrudingportion130 will cause the exhaust gases to have a static pressure at their periphery during their outward expansion that causes the free stream to turn isentropically.

Eventually, the exhaust gases will move past trailingend134, at whichpoint plug body128 will have no further influence on the expansion of the exhaust gases. Shortly thereafter, the exhaust gases will reach a fully expanded state wherein the static pressure of the exhaust gas will be equal to the static pressure of the free stream. From this point on, the exhaust gasses (exhaust plume82) and the free stream will flow parallel to one another in the downstream direction.

The effect that plugbody128 has on the free stream can be summarized as follows. The free stream is turned from a direction that is tangential to the outer walls of trailingedge126 to a direction that is parallel to the longitudinal axis ofsupersonic jet engine90. During this transitional phase, the free stream is turned as a result of the static pressure exerted by the exhaust gases. The contour ofplug body128 controls the static pressure of the exhaust gases. Thus, by selecting an appropriate contour and configuration forplug body128, the free stream can be turned isentropically without shock.

FIG. 9 illustrates a portion of aninlet arrangement92 in an expanded view. This view compares a conventional supersonic jet engine having a conventional center body146 (shown in phantom) with asupersonic jet engine90 equipped withcenter body102. The conventional supersonic jet engine has aconventional cowl148 and aconventional bypass splitter150 whilesupersonic jet engine90 hascowl98 and abypass splitter120. As can be seen,cowl98 has a much shallower angle thanconventional cowl148 with respect to a free stream direction. This reduction in cowl angle is made possible bycenter body102 which, as set forth above, has a protruding portion that has a length that exceeds a conventional spike length. The additional length ofcenter body102 providescenter body102 with an opportunity to turn the direction of the free stream flowing overcenter body102 in a direction that is more axially aligned with a longitudinal axis ofsupersonic jet engine90. The angle ofbypass splitter120 has also been changed to accommodate the oncoming flow ofair entering inlet116 acrossterminal shock144 which has a more longitudinal flow direction. By permitting such a sharp reduction in the cowl angle,center body102 contributes to a substantial reduction in the strength of the cowl shock produced bycowl lip100.

FIG. 10 provides a visual depiction of a technique for designingplug body128. Depending upon the anticipated use ofsupersonic jet engine90, a designer will select a downstream location where it is desirable for the exhaust gases to reach a fully expanded state and begin to flow parallel to the direction of the free stream. InFIG. 10, this location is identified by arrow heads152.Arrowheads152 are spaced apart by a distance equal to the diameter of exhaust plume82 (seeFIG. 8) which corresponds with the known output ofturbo machinery96. Although the location ofarrowheads152 in the longitudinal direction may vary based on design criteria, their distance from one another in the lateral direction is fixed based on the power setting ofturbo machinery96.

Once the designer has selected the location forarrowheads152, the next step is to determine the location for trailingend134 ofplug body128. The location of trailingend134 is determined based on the well-known principle of Mach line propagation. Mach lines will propagate off of a surface in a supersonic flow at an angle β which is determined by the following equation:
β=arcsine(1/Mach number)

Accordingly, for a known Mach speed of the exhaust gases traveling past trailingend134, aMach line154 will propagate off of trailingend134 at angle β. Using both angle β and the location of the arrow heads, the location of trailingend134 can be determined by positioning an end of eachMach line154 on eacharrowhead152 and, looking in an upstream direction, determining where the Mach lines intersect. That point of intersection is the location where trailingend134 will be located. Once the location of trailingend134 is determined, the overall length ofbody plug128 can be determined.

Next, a desired curvature is selected for the turning of the free stream. This curvature is represented byphantom line155 and is selected by the nozzle designer. One criteria may be to choose a curvature that will result in an isentropic change in direction of the free stream. Once the desired curvature is selected, the contours and configuration ofplug body128 can be determined using Method of Characteristics. When utilizing Methods of Characteristics,phantom line155 is considered to be a boundary condition and the contours and configuration ofplug body128 is calculated by selecting a curvature forplug body128 that will cause the exhaust gases to conform tophantom line155. Other techniques such as the use of computational fluid dynamics software may also be utilized when determining the geometry ofplug body128.

FIG. 11 is a flow diagram illustrating a method156 for making an inlet arrangement for use with a supersonic jet engine that is configured to consume air at a predetermined mass flow rate when the supersonic jet engine is operating at a predetermined power setting and moving at a predetermined Mach speed.

At step158, a cowl, a center body and a bypass splitter are provided. In some embodiments, the supersonic engine may not include a bypass. For such embodiments, this step would not include providing a bypass splitter. The cowl has a cowl lip. The center body has an apex, a first compression surface located downstream of the apex, and a second compression surface located downstream of the first compression surface.

At step160, the center body is positioned with respect to the cowl such that the center body is coaxial with the cowl, a protruding portion of the center body extends upstream of the cowl lip for a length that is greater than a conventional spike length, and the second compression surface is spaced apart from the cowl lip such that the second compression surface and the cowl lip define an inlet.

At step162, for supersonic engines that are configured with a bypass splitter, the bypass splitter is positioned between the cowl and the center body to form a bypass that is configured to receive air at a second predetermined mass flow rate when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed.

When properly implemented, method steps158-162 will yield an inlet arrangement where the protruding portion of the center body is configured to divert a flow of air that is located in a path of the inlet out of the path of the inlet such that a remaining flow of air that approaches and enters the inlet is not greater than the predetermined mass flow rate when the jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed. For embodiments of the supersonic jet engine that include the bypass, the center body is configured to divert the flow of air that is located in the path of the inlet out of the path of the inlet such that the remaining flow of air approaching and entering the inlet is not greater than the first predetermined mass flow rate (i.e., the predetermined rate at which air is consumed by the turbo machinery of the supersonic jet engine) and the second predetermined mass flow rate (i.e., the rate at which the by-pass routes airflow around the turbo machinery) combined when the jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed.

FIG. 12 is a flow diagram illustrating a method164 for making a nozzle arrangement for use with a supersonic jet engine that is configured to produce a plume of exhaust gases when the engine is operating at a predetermined power setting and moving at a predetermined Mach speed.

At step166 a nozzle, a plug body, and a bypass wall are provided. In some embodiments, a bypass will not be utilized. For such embodiments, a bypass wall will not be provided. The nozzle is configured to exhaust the plume of exhaust gases and has a trailing edge oriented at a predetermined angle with respect to an axial direction of the nozzle. The plug body has an expansion surface and a compression surface downstream of the expansion surface.

At step168, the plug body is positioned with respect to the nozzle such that the plug body is partially positioned within the nozzle and coaxially aligned therewith and such that a protruding portion of the plug body extends downstream of the trailing edge for a length greater than a conventional plug body length.

At step170, for embodiments that utilize a bypass, the bypass wall will be positioned between the nozzle and the plug body.

When properly implemented, method steps166-170 will yield a nozzle arrangement wherein the protruding portion of the plug body will have a substantially circular cross-section along substantially an entire longitudinal length of the protruding portion of the plug body. The plug body will be configured to shape the plume of exhaust gases such that the plume of exhaust gases flows substantially parallel to a direction of the free stream of air flowing off of the trailing edge of the nozzle proximate the trailing edge of the nozzle and wherein the plug body is further configured to cause the plume of exhaust gases to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle at a location downstream of the trailing edge of the nozzle such that the free stream of air flowing off of the trailing edge moves in a direction parallel to a longitudinal axis of the plug body. In embodiments that utilize a bypass, the plug body will be configured to cause the plume of exhaust gases and a bypass airflow to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle to the direction parallel to the longitudinal axis of the plug body at a location downstream of a trailing end of the plug body.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the disclosure, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the disclosure as set forth in the appended claims.

Claims (19)

What is claimed is:

1. A nozzle arrangement for use with a supersonic jet engine configured to produce a plume of exhaust gases when the supersonic jet engine is operating at a predetermined power setting and moving at a predetermined Mach speed, the nozzle arrangement comprising:

a nozzle configured to exhaust the plume of exhaust gases, the nozzle having a trailing edge; and

a plug body partially positioned within the nozzle and coaxially aligned with the nozzle, the plug body having an expansion surface and a compression surface downstream of the expansion surface, a protruding portion of the plug body extending downstream of the trailing edge, the protruding portion of the plug body having a concave surface proximate a terminus of the plug body, the plug body having contours and dimensions configured to shape the plume of exhaust gases such that the plume of exhaust gases flows substantially parallel to a direction of a free stream of air flowing off of the trailing edge of the nozzle proximate the trailing edge of the nozzle when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed and has further contours and dimensions that are configured to cause the plume of exhaust gases to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle at a location downstream of the trailing edge of the nozzle such that the free stream of air flowing off of the trailing edge moves in a direction parallel to a longitudinal axis of the plug body when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed.

2. The nozzle arrangement ofclaim 1, wherein the compression surface comprises an isentropic compression surface.

3. The nozzle arrangement ofclaim 1, wherein a portion of the expansion surface is upstream of the trailing edge of the nozzle.

4. The nozzle arrangement ofclaim 1, wherein the plug body is configured to cause the plume of exhaust gases to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle to the direction parallel to the longitudinal axis of the plug body at a location downstream of a trailing edge of the plug body.

5. The nozzle arrangement ofclaim 1, wherein the trailing edge of the nozzle is substantially axisymmetric and wherein the trailing edge of the nozzle and the expansion surface of the plug body define an annular outlet of the nozzle.

6. The nozzle arrangement ofclaim 1, wherein the expansion surface and the compression surface are contiguous with one another.

7. The nozzle arrangement ofclaim 6, wherein a surface of the plug body is devoid of discrete discontinuities in a region where the expansion surface transitions into the compression surface.

8. A nozzle arrangement for use with a supersonic jet engine configured to produce a plume of exhaust gases when the supersonic jet engine is operating at a predetermined power setting and moving at a predetermined Mach speed, the nozzle arrangement comprising:

a nozzle configured to exhaust the plume of exhaust gases, the nozzle having a trailing edge;

a plug body partially positioned within the nozzle and coaxially aligned with the nozzle; and

a bypass wall disposed between the nozzle and the plug body configured to direct a bypass airflow out of the nozzle, the plug body having an expansion surface and a compression surface downstream of the expansion surface, a protruding portion of the plug body extending downstream of the trailing edge, the protruding portion of the plug body having a concave surface proximate a terminus of the plug body, the plug body having contours and dimensions configured to shape the plume of exhaust gases and the bypass airflow such that the plume of exhaust gases and the bypass airflow flow substantially parallel to a direction of a free stream of air flowing off of the trailing edge of the nozzle proximate the trailing edge of the nozzle when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed and has further contours and dimensions that are configured to cause the plume of exhaust gases and the bypass airflow to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle at a location downstream of the trailing edge of the nozzle such that the free stream of air flowing off of the trailing edge moves in a direction parallel to a longitudinal axis of the plug body when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed.

9. The nozzle arrangement ofclaim 8, wherein the compression surface comprises an isentropic compression surface.

10. The nozzle arrangement ofclaim 8, wherein a portion of the expansion surface is upstream of the trailing edge of the nozzle.

11. The nozzle arrangement ofclaim 8, wherein the plug body is configured to cause the plume of exhaust gases and the bypass airflow to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle to the direction parallel to the longitudinal axis of the plug body at a location downstream of a trailing edge of the plug body.

12. The nozzle arrangement ofclaim 8, wherein the trailing edge of the nozzle is substantially axisymmetric and wherein the trailing edge of the nozzle and the expansion surface of the plug body define an annular outlet of the nozzle.

13. The nozzle arrangement ofclaim 8, wherein the expansion surface and the compression surface are contiguous with one another.

14. The nozzle arrangement ofclaim 13, wherein a surface of the plug body is devoid of discrete discontinuities in a region where the expansion surface transitions into the compression surface.

15. A method of making a nozzle arrangement for use with a supersonic jet engine configured to produce a plume of exhaust gases when the supersonic jet engine is operating at a predetermined power setting and moving at a predetermined Mach speed, the nozzle arrangement method comprising:

providing a nozzle configured to exhaust the plume of exhaust gases, the nozzle having a trailing edge, and a plug body having an expansion surface and a compression surface downstream the expansion surface;

positioning the plug body with respect to the nozzle such that the plug body is partially positioned within the nozzle and coaxially aligned therewith and such that a protruding portion of the plug body extends downstream of the trailing edge,

wherein the protruding portion of the plug body has a concave surface proximate a terminus of the plug body,

wherein the plug body has contours and dimensions configured to shape the plume of exhaust gases such that the plume of exhaust gases flows substantially parallel to a direction of a free stream of air flowing off of the trailing edge of the nozzle proximate the trailing edge of the nozzle when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed, and

wherein the plug body has further contours and dimensions that are configured to cause the plume of exhaust gases to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle at a location downstream of the trailing edge of the nozzle such that the free stream of air flowing off of the trailing edge moves in a direction parallel to a longitudinal axis of the plug body when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed.

16. The method ofclaim 15, wherein providing the plug body having an expansion surface and a compression surface downstream of the expansion surface comprises providing a plug body wherein the compression surface is an isentropic compression surface.

17. The method ofclaim 15, wherein providing the plug body having an expansion surface and the a compression surface downstream of the expansion surface comprises providing a plug body wherein the expansion surface is contiguous with the compression surface.

18. The method ofclaim 17, wherein providing the plug body having wherein the expansion surface that is contiguous with the compression surface comprises providing a plug body wherein the plug body lacks lacking any discrete discontinuities between the expansion surface and the compression surface.

19. A method of making a nozzle arrangement for use with a supersonic jet engine configured to produce a plume of exhaust gases when the supersonic jet engine is operating at a predetermined power setting and moving at a predetermined Mach speed, the nozzle arrangement method comprising:

providing a nozzle configured to exhaust the plume of exhaust gases, the nozzle having a trailing edge, and a plug body having an expansion surface and a compression surface downstream the expansion surface;

positioning the plug body with respect to the nozzle such that the plug body is partially positioned within the nozzle and coaxially aligned therewith and such that a protruding portion of the plug body extends downstream of the trailing edge;

providing a bypass wall and positioning the bypass wall between the nozzle and the plug body,

wherein the protruding portion of the plug body has a concave surface proximate a terminus of the plug body,

wherein the plug body has contours and dimensions configured to shape the plume of exhaust gases and a bypass flow such that the plume of exhaust gases and the bypass flow both flow substantially parallel to a direction of a free stream of air flowing off of the trailing edge of the nozzle proximate the trailing edge of the nozzle when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed, and

wherein the plug body has further contours and dimensions that are configured to cause the plume of exhaust gases and the bypass flow to isentropically turn the free stream of air flowing off of the trailing edge of the nozzle at a location downstream of the trailing edge of the nozzle such that the free stream of air flowing off of the trailing edge moves in a direction parallel to a longitudinal axis of the plug body when the supersonic jet engine is operating at the predetermined power setting and moving at the predetermined Mach speed.

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