Exhaust nozzle

Abstract

The present invention relates to an exhaust nozzle for fluid thrust vectoring comprising an elongated channel for directing exhaust gases having first and second ends. The elongated channel has an inlet at the first end with a continuously curved cross-sectional shape and an outlet at the second end with a polygonal cross-sectional shape. In a preferred embodiment, the exhaust nozzle has an outlet of rectangular cross-section. A jet engine and an aircraft having the exhaust nozzle are also provided.

Description

[Technical field]

[0001] The present invention relates to an exhaust nozzle for channelling the thrust generated by a jet engine or rocket, particularly, but not exclusively, for use in a jet engine or aircraft. [Background technology]

[0002] The nozzle is the aft end of the exhaust pipe (or duct) which directs the thrust from the engine.

[0003] Fluidic thrust vectoring using two-dimensional (2D) nozzles (i.e., slits) is currently well known. Three-dimensional (3D) nozzles are also commonly known, but making them work for fluidic thrust vectoring has been difficult. Various exhaust geometric parameters, such as nozzle shape and bypass duct diameter, have been studied in the past. Rectangular nozzles, such as those found on the Lockheed Martin F-22 Raptor, are preferred. Circular nozzles are also known as axisymmetric nozzles.

[0004] Thrust vectoring is the ability of a vehicle, such as an aircraft or rocket, to manipulate the direction of the exhaust flow from its engine(s) or motor(s) in order to control the attitude or angular velocity of the vehicle. Thrust vectoring flight control is obtained through vectoring of the thrust generated by the vehicle's engines in the pitch and / or yaw directions. This may be accomplished by mechanical means such as pivoting a nozzle with a hinge. Fluid thrust vectoring is the manipulation or control of the exhaust flow using a secondary air source, typically bleed air from the engine compressor or fan.

[0005] The Dual Throat Nozzle (DTN) concept was developed by NASA Langley Research Centre in 2003 based on the throat shifting method. It is shown in Figure 1. A concave cavity section 3 is located between an upstream minimum area (conventional nozzle throat) and a downstream minimum area (exit throat). A fluid jet 1 is introduced at the upstream minimum area location. This concept combines the thrust efficiency of the throat skewing thrust vectoring method with the increased thrust vector efficiency obtained by maximizing the pressure difference in a separated cavity flow 2 located downstream of the first nozzle throat.

[0006] The thrust vectoring efficiency of the DTN has been shown to be higher than that of Shock Vector Control (SVC) and throat shift methods, and has been the subject of numerous research studies conducted by NASA. These studies cover a wide range of nozzle designs and operating conditions. Configurations range between those with rectangular cross sections and those with circular cross sections, and nozzles are operated in single-axis and dual-axis modes.

[0007] Further design enhancements to the DTN nozzle concept to enable its use on supersonic aircraft include varying the nozzle area and employing a "bypass DTN" approach where throat bypass is injected into the cavity between the two throats. The latter bypass approach is shown in Figure 2. Altering the divergence and convergence angles of cavity 3 combined with wall curvature resulted in a significant increase in the achievable thrust vector angle and thrust vectoring efficiency.

[0008] The bypass DTN does not have a separate bleed from the engine compressor, but instead uses exhaust gases from upstream of the throat convergence for secondary injection 5. A bypass duct 4 containing a control valve is used to controllably deliver exhaust gases 1 from the primary nozzle upstream of the throat contraction into the injection nozzle at the throat.

[0009] Eliminating the oblique shock prevents the flow from turning too early and allows for greater vectoring in the subsonic flow region downstream of the normal shock.

[0010] This approach of using the primary nozzle bypass 4 avoids the complexity and cost of providing a dedicated compressor bleed discharge and transfer duct and eliminates the impact of the bleed discharge on engine performance and stability.

[0011] Known prior art exhaust ducts provide either: 1) an axisymmetric nozzle, where the entire exhaust duct has an axisymmetric (circular) cross-section along its length (from the turbine exit through the throat to the nozzle exit), or 2) a rectangular nozzle, where the entire exhaust duct has a rectangular / square cross-section along its length (from the turbine exit through the throat to the nozzle exit).

[0012] The inventors have designed a 3D exhaust nozzle geometry that allows for combined nearly monotonic pitch and yaw vectoring of the exhaust jet through a rectangular nozzle exit. This avoids the tendency of the jet to vector only in two orthogonal directions defined by the nozzle exit geometry. This problem is not solved by known prior art designs. Summary of the Invention

[0013] According to a first aspect of the present invention, An elongated channel for directing exhaust gas having a first end and a second end, the elongated channel having an inlet at the first end with a continuously curved cross-sectional shape and an outlet at the second end having a polygonal cross-sectional shape. An exhaust nozzle for fluidic thrust vectoring is provided, comprising:

[0014] Advantageously, the present invention provides a three-dimensional exhaust nozzle that transitions directly from the turbine outlet shape to a shape that offers several advantages for fluidic thrust vectoring. Although rectangular outlets are known, they are not provided in three-dimensional nozzles, and transitions from a circular cross-sectional shape to a polygonal cross-sectional shape in the same nozzle are not known, which tends to reduce complexity.

[0015] The exhaust nozzle is an expansion region having an inlet, wherein a cross-sectional area of ​​a discharge nozzle in the expansion region increases with distance from the inlet toward the contraction region; a convergence region having an outlet and coupled to the expansion region at an end of the expansion region opposite the inlet, wherein a cross-sectional area of ​​the exhaust nozzle decreases with distance from the convergence region toward the outlet, the convergence region and the expansion region together defining a channel; Equipped with.

[0016] The constriction region may form 15% to 40% of the length of the exhaust nozzle. Preferably, the constriction region forms 20% to 30% of the length of the exhaust nozzle. Even more preferably, the constriction region forms about 25% of the length of the exhaust nozzle.

[0017] The inlet may have a circular cross-sectional shape. Alternatively, the inlet may have an elliptical cross-sectional shape.

[0018] The outlet may have a rectangular cross-sectional shape. Alternatively, the outlet may have a square cross-sectional shape. Alternatively, the outlet may have a triangular cross-sectional shape.

[0019] The channels may be free of corners, in other words the channels may have surfaces that meet at an angle between 120 degrees and 180 degrees, preferably the channels may have surfaces that meet at an angle between 140 degrees and 180 degrees.

[0020] The constriction region may comprise a plurality of joined tessellated panels to change the cross-sectional shape of the channel from a continuous curve to an intermediate cross-sectional shape before the outlet cross-sectional shape is formed. Each panel may be triangular and may be arranged such that adjacent panels are inverted relative to each other to form a uniform outlet surface.

[0021] The nozzle cross-sectional shape may transition from a continuous curve to an outlet cross-sectional shape between the second end and 20% of the length of the exhaust nozzle as measured from the second end. Alternatively, the nozzle cross-sectional shape may transition from a continuous curve to an outlet cross-sectional shape between the second end and 15% of the length of the exhaust nozzle as measured from the second end. Alternatively, the nozzle cross-sectional shape may transition from a continuous curve to an outlet cross-sectional shape between the second end and 10% of the length of the exhaust nozzle as measured from the second end. Alternatively, the nozzle cross-sectional shape may transition from a continuous curve to an outlet cross-sectional shape between the second end and 5% of the length of the exhaust nozzle as measured from the second end.

[0022] According to a second aspect of the present invention, there is provided a jet engine comprising an exhaust nozzle according to the first aspect.

[0023] According to a third aspect of the present invention, there is provided an aircraft comprising an exhaust nozzle according to the first aspect. [Brief description of the drawings]

[0024] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which: [Figure 1] FIG. 1 shows a schematic diagram of a prior art DTN. [Diagram 2] FIG. 2 shows a schematic diagram of an improved DTN according to the prior art. [Figure 3a]FIG. 3a shows a cross-section through a nozzle according to one embodiment. [Figure 3b] FIG. 3b shows a longitudinal section through a nozzle according to an embodiment, taken along line AA in FIG. 3a. [Figure 4a] Figures 4a and 4b show perspective views of a nozzle according to one embodiment looking from the outlet towards the inlet. [Figure 4b] Figures 4a and 4b show perspective views of a nozzle according to one embodiment looking from the outlet towards the inlet. [Figure 5a] FIG. 5a shows a perspective view of the end of a nozzle according to one embodiment. [Figure 5b] FIG. 5b shows a perspective view looking rearward from the inside of the end of the nozzle of FIG. 5a (nearby surfaces removed). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] In general, the embodiments relate to an exhaust nozzle that transitions from a circular or elliptical cross section at its inlet (throat) to an outlet having a rectangular cross section. While an outlet with a rectangular cross section is beneficial, the turbine and resulting outlet are necessarily circular. Thus, the described embodiments provide an optimal way to transition the exhaust nozzle from a circular to a rectangular cross section in order to maximize overall propulsion efficiency along with vectoring efficiency and effectiveness (especially when combined two-axis vectoring for pitch and yaw control needs to be achieved).

[0026] 3a and 3b show cross-sectional views through an exhaust nozzle 100 according to one embodiment. The exhaust nozzle 100 defines a cavity. The exhaust nozzle 100 comprises an expansion region 12 and a contraction region 10. The expansion region 12 comprises a throat 20 for receiving exhaust gases from a turbine outlet. The throat 20 is the region where a compressed gas jet used for vectoring control is introduced into the exhaust nozzle 100. The throat 20 has a circular cross-section to match the cross-section of the turbine outlet. In another embodiment, the throat 20 has an elliptical cross-section to match the turbine outlet. The throat 20 is where the exhaust nozzle 100 reaches its first smallest cross-sectional area downstream of the turbine outlet.

[0027] The cross-section of the expansion region 12 increases in area between the throat 20 and the point where it intersects with the contraction region 10. If the aspect ratio of the nozzle exit 18 is not 1:1 (i.e., not square), then the internal cross-section of the expansion region 12 transitions from circular at the throat 20 to elliptical at the point where it intersects with the contraction region 10. In other words, the inner wall of the expansion 12 is smooth and curved, maintaining a continuity of curvature.

[0028] The contraction region 10 is provided with an outlet 18 through which the exhaust gases exit the nozzle 100 to mix with the atmosphere. The outlet 18 is an opening (or orifice) in the exterior surface of the nozzle 100 that provides access to a cavity within the nozzle 100 for channeling the exhaust gases. The outlet 18 has a rectangular cross-section. In alternative embodiments, the outlet 18 has a square, triangular, pentagonal, or hexagonal cross-section. Typically, the outlet 18 has a non-circular cross-section.

[0029] The contraction region 10 transitions from its maximum axial cross-sectional area (ie, diameter) at the point where it meets the expansion region 12 to its minimum axial cross-sectional area (ie, diameter) at the outlet 18 .

[0030] The contraction region 10 typically occupies 15% to 25% of the length of the nozzle 100 (ie, between the throat 20 and the outlet 18).

[0031] The transition from a circular cross section to a rectangular nozzle exit 18 is best achieved during the final short contraction region 10 of the nozzle 100. The final transition from an elliptical to a rectangular cross section is best achieved using a mathematical surface geometry approach that avoids the formation of strong corners until the face of the exit 18 is reached. The face of the exit 18 is an artificial plane that touches all parts of the nozzle that form the lip of the exit 18. If corners (i.e., interior panels that intersect at an angle less than 120 degrees) are formed too far forward of the face of the exit 18, the ability to achieve uniform and monotonically varying two-axis (combined pitch and yaw) vectoring of the exhaust jet is compromised.

[0032] Introducing sharp corners in the nozzle 100 tends to bias the vectoring to "snap" toward either of the orthogonal directions of the outlet 18. In other words, the interior geometry of the constriction region 10 is designed such that no corners are formed along the vertices 24 leading to the outlet 18. A corner is defined here as a panel vertex that meets at an angle of less than 110 degrees, preferably less than 110 degrees, more preferably less than 120 degrees, and even more preferably less than 130 degrees. In other words, most preferably, the panels 22 are positioned or designed to meet at an angle of 130 degrees or greater in the constriction region 10. These vertices 24 are more clearly illustrated in Figures 3b, 5a, and 5b. Figures 5a and 5b illustrate different perspective views of the constriction region 10 as described above.

[0033] FIG. 3b is a cross-sectional view through line A-A in FIG. 3a. FIG. 3b shows that one panel 22a forming the inner surface of the contraction region 10 is planar while the adjacent panel (22b) may be curved. This allows for a gradual transition from the throat 20, which has a cross-section with a continuity of curvature, to the outlet 18, which has completely straight sides. As the outlet 18 is approached, the panels 22 become more straight until the cross-sectional shape of the nozzle completely transforms to the cross-sectional shape of the outlet 18. The panels 22 are positioned to optimize the transition from the curved cross-section to the straight cross-section, while ensuring that no corners (i.e. angles less than 120 degrees) are formed between the panels 22.

[0034] One solution to this problem, i.e., avoiding the formation of corners, is to use triangular panels 22 to form the interior surface of the constriction area 10. Other, more complex mathematical surface generation can achieve even better performing transition surfaces. For example, the panels 22 may not be perfectly flat or curved, but a combination thereof. The panels 22 may be irregularly shaped as they progress from a wide base to a narrow tip. The panels 22 are tessellated with one another.

[0035] The transition from a smoothly curved cross-section (e.g., circle or ellipse) to a rectangular duct exit 18 occurs during the final nozzle 100 contraction. Preferably, the final transition occurs in the last 5%-15% of the nozzle 100 length measured from the throat 20 to the face of the exit 18. In other words, the cross-sectional area of ​​the nozzle 100 decreases throughout the contraction region 10, but in the last 5%-15% of the nozzle 100 length, the cross-sectional shape gradually changes to that of the exit 18. The function of this final contraction is to change the shape of the internal nozzle structure, control the exit area, and provide a final turning of the jet to achieve vectoring.

[0036] Experimental data indicates that the above approach tends to enable thrust vectoring angles of up to about 15 degrees in a 45 degree combined pitch / yaw plane. Nozzles 100 created with a transition surface with a corner funnelling directly into the corner of the exit 18 (i.e., an edge along the apex 24) can only achieve 2-4 degrees of vectoring in a 45 degree combined pitch / yaw plane, and the exhaust jet has a tendency to flip in either the pitch or yaw plane when actuated to achieve a combined pitch / yaw vector angle.

[0037] This approach is applicable to all fluidic thrust vectoring schemes that use fluid injection at the nozzle throat 20 to achieve vectoring of a jet exiting through a rectangular (or possibly any non-elliptical) outlet 18. For example, the nozzle 100 described herein above is applicable to DTN and bypass DTN exhaust ducts.

[0038] The exhaust nozzle 100 may be mounted at the rear of an aircraft to direct thrust from a jet engine or rocket motor, where the jet engine may be a ramjet, scramjet, turboprop, turbofan, turbojet, or turboshaft engine. The exhaust nozzle 100 is further applicable to a water jet. Thus, instead of an aircraft, the exhaust nozzle 100 may be applied to a ship or spacecraft.

Claims

1. 1. An exhaust nozzle for fluid thrust vectoring, comprising: An elongated channel for directing exhaust gas having a first end and a second end, the elongated channel having an inlet at the first end with a continuously curved cross-sectional shape and an outlet at the second end having a polygonal cross-sectional shape. An exhaust nozzle comprising:

2. an expansion region having the inlet, wherein the cross-sectional area of ​​the discharge nozzle in the expansion region increases with distance from the inlet toward a contraction region; a convergence region having the outlet and coupled to the divergence region at the end of the divergence region opposite the inlet, wherein the cross-sectional area of ​​the exhaust nozzle decreases with distance from the convergence region toward the outlet; the expanding region and the contracting region together define the channel; The exhaust nozzle of claim 1 , comprising:

3. The exhaust nozzle of claim 2 , wherein the constriction region forms between 15% and 40% of the length of the exhaust nozzle.

4. An exhaust nozzle as claimed in any preceding claim, wherein the inlet has a circular cross-section.

5. An exhaust nozzle as claimed in any preceding claim, wherein the outlet has a rectangular cross-section.

6. An exhaust nozzle as claimed in any preceding claim, wherein the channels have surfaces that meet at an angle between 120 degrees and 180 degrees.

7. 7. The exhaust nozzle of claim 1, wherein the contraction region comprises a plurality of joined tessellated panels to change the cross-sectional shape of the channel from a continuous curve to an intermediate cross-sectional shape before the outlet cross-sectional shape is formed.

8. 8. The exhaust nozzle of claim 7, wherein each panel is triangular and adjacent panels are inverted relative to each other and arranged to form a uniform exit face.

9. 9. The exhaust nozzle of claim 1, wherein the nozzle cross-sectional shape transitions from a continuous curve to the outlet cross-sectional shape between the second end and 20% of the length of the exhaust nozzle as measured from the second end.

10. A jet engine comprising the exhaust nozzle according to any one of claims 1 to 9.

11. An aircraft comprising the exhaust nozzle according to any one of claims 1 to 9.

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