Embedded air inlet based on swept step to displace the forebody boundary layer

Abstract

The present invention proposes a submerged air inlet based on a swept step to displace the forebody boundary layer. The swept step is used to displace the forebody boundary layer entering the submerged air inlet to both sides, and the boundary layer is discharged away from the inner channel entrance through the guide channel. The swept step can reduce the flow loss caused by the forebody boundary layer and improve the total pressure recovery coefficient. The present invention has a simple structure and is easy to implement. It can achieve the expected effect after numerical simulation verification.

Description

Technical Field

[0001] The invention relates to the field of aircraft design, in particular to a buried air inlet. Background Art

[0002] Modern warfare places high demands on aircraft performance. Modern aircraft not only need to pursue higher tactical performance, namely high speed, high maneuverability, low-altitude penetration and downward vision capabilities, but also need to improve the aircraft's survivability, namely stealth capability. At present, stealth capability is mainly reflected in reducing the radar scattering area. Studies have shown that the use of buried air intakes can significantly reduce the radar scattering area.

[0003] The embedded air inlet is a subsonic air inlet that has its inlet entrance buried in the fuselage surface and has no raised parts. Since the air inlet has no raised parts, it will not increase the additional frontal area of ​​the aircraft. It has many advantages such as small aerodynamic drag, good stealth performance, and convenient box-type launch. Therefore, it has attracted widespread attention from researchers at home and abroad. At present, this air inlet has been used on many models of aircraft. Since the existing embedded air inlet cannot be set with a boundary layer separator, the boundary layer of the airflow entering the air inlet is thick, which has an adverse effect on the performance of the entire air inlet. For this reason, it is necessary to develop a new embedded air inlet boundary layer control method to improve the total pressure recovery coefficient of the embedded air inlet. Summary of the invention

[0004] In order to improve the total pressure recovery coefficient of the air inlet without adding additional complex structures, the present invention provides a buried air inlet based on a swept step to displace the forebody boundary layer.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A buried air inlet based on a swept step displacement front body boundary layer comprises an air inlet inlet, a rear lip located at the rear end of the air inlet inlet and extending within the air inlet inlet range, a guide surface recessed inwardly from the air inlet inlet, an inner channel formed by extending rearwardly from the rear lip, and guide channel surfaces located on both sides of the rear lip, wherein the inner channel comprises an arc-shaped inner surface located in the rear lip, the two sides of the arc-shaped inner surface are respectively connected to the two sides of the rear lip to form an integral channel structure, and a guide surface extends from the two sides of the rear lip to the middle. A swept profile line is formed by extending from the middle to the sides to form a swept profile line located at a relatively forward position of the leading edge of the rear lip, a swept step surface is also provided between the swept profile line and the guide surface, the leading edge of the swept step surface is connected to the guide surface, the trailing edge of the swept step surface is connected to the swept profile line, and a trough-shaped depression is formed at the connection between the swept step surface and the guide surface, and a crest-shaped protrusion is formed at the connection between the trailing edge of the swept step surface and the swept profile line; the swept step surface forms a swept extension from the middle to both sides until it is smoothly transitioned to the guide channel surfaces on both sides of the rear lip.

[0007] The present invention sets a swept step at the downstream position of the guide surface, so that the thicker boundary layer developed along the fuselage can be discharged to both sides by the swept step and discharged out of the air inlet through the guide channel, thereby reducing the influence of the boundary layer on the performance of the air inlet. By setting the swept step, while achieving the advantages of the buried air inlet, the thicker boundary layer is cleverly eliminated, thereby improving the total pressure recovery coefficient of the air inlet. At the same time, the present invention has the advantages of simple structure, no additional weight for the aircraft, easy implementation, and basically no occupation of the body space. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a schematic diagram of the three-dimensional structure of the half-mold configuration of the embedded air inlet of the present invention;

[0009] Figure 2 It is a bottom view of the embedded airway half-mold configuration of the present invention;

[0010] Figure 3 It is a schematic diagram of the three-dimensional structure of the buried air inlet port surface of the present invention;

[0011] Figure 4 It is the total pressure distribution spectrum along the cross section of the prototype buried inlet;

[0012] Figure 5 It is a total pressure distribution spectrum along the cross section of the buried air inlet with a swept step of the present invention;

[0013] Figure 6 It is the total pressure distribution map of the prototype buried inlet duct outlet section;

[0014] Figure 7 It is a total pressure distribution spectrum of the outlet cross section of the buried air inlet with a swept step of the present invention;

[0015] Figure 8 It is a static pressure distribution map of the wall surface of the embedded air inlet with a swept step of the present invention. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below with reference to the accompanying drawings.

[0017] See also Figures 1 to 3As shown, the present invention discloses a buried air inlet based on a swept step displacement front body boundary layer, the buried air inlet is located on the aircraft fuselage and has an aircraft fuselage outer surface 1 that is integrated with the aircraft fuselage. The air inlet inlet forms a buried air inlet structure inward from the aircraft fuselage outer surface 1. The buried air inlet also includes a rear lip 2 located at the rear end of the air inlet inlet and extending into the air inlet inlet range, a guide surface 3 recessed inward from the air inlet inlet, a side edge 4 transitioning between the guide surface 3 and the aircraft fuselage outer surface 1, an inner channel 5 extending backward from the rear lip 2, and a guide channel surface 6 located on both sides of the rear lip 2.

[0018] The inner channel 5 includes an arc-shaped inner surface 7 located inside the rear lip 2, and the two sides of the arc-shaped inner surface 7 are respectively connected to the two sides of the rear lip 2 to form an integral channel structure. A swept profile 8 located at a relatively forward position of the front edge of the rear lip is formed by extending from the two sides of the rear lip 2 to the middle, and a swept step surface 9 is also provided between the swept profile 8 and the guide surface 3. The front edge of the swept step surface 9 is connected to the guide surface 3, and the rear edge of the swept step surface 9 is connected to the swept profile 8. The guide channel surface 6, the side edge 4 and the outer side of the rear lip 2 form a guide channel, and the guide channel surface 6 extends obliquely from the inside to the outside, and the guide channel surface 6 is smoothly transitionally connected to the swept step surface at the inner end, and the guide channel surface 6 is connected to the outer surface 1 of the aircraft fuselage at the outer end.

[0019] The swept-back profile 8 is a symmetrical profile. The front end of the swept-back profile 8 forms a sharp point, and extends from the sharp point to both sides to form an arc-shaped profile. The profile of the leading edge of the swept-back step surface 9 also forms a sharp point at the front end, extends from the sharp point to both sides to form an arc-shaped symmetrical profile, and the swept-back step surface 9 forms a swept extension from the middle to both sides until it smoothly transitions to the guide channel surfaces 6 on both sides of the rear lip 2.

[0020] In this embodiment, the air inlet guide surface 3 intersects with the swept step surface 9, and the junction of the two walls is chamfered. The side edges 4 are located on both sides of the air inlet guide surface 3, and the junction of the walls is chamfered. The front edge of the rear lip 2 is swept back on both sides, forming a horizontal "Λ" shape. The intersection of the swept step surface 9 and the swept profile 8 is chamfered. The guide channel 6 is located between the rear lip 2 and the side edges 4, and gradually develops from the inside of the air inlet to the surface of the fuselage.

[0021] When the airflow entering the embedded air inlet flows through the guide surface 3 to the swept step surface 9, the step surface generates a strong local adverse pressure gradient on the incoming flow. The existence of the lateral pressure gradient causes the low-energy fluid in the boundary layer to be guided along the swept step surface 9 to the guide channel where the guide channel surface 6 is located, and then discharged out of the air inlet.

[0022] Application Examples

[0023] Solution Introduction:

[0024] A baseline prototype buried inlet and a buried inlet with swept steps are designed, with a cruise Mach number of 0.72 and an exit Mach number of 0.45. The side angle of the inlet is 4°, the guide angle is 17°, the inner channel area expansion ratio is 1.18, and the exit diameter is 256mm. The swept step is a wide, h high, and the step sweep angle is α, satisfying 0.40D≤a≤0.41D, 0.23D≤h≤0.24D, 30°≤α≤33°, where D is the inner channel diameter. The baseline prototype buried inlet and the buried inlet with swept steps are compared and analyzed through three-dimensional numerical simulation.

[0025] like Figure 4 , Figure 6 As shown, in the prototype embedded inlet scheme in the existing technology, there is a thicker forebody boundary layer in front of the inlet entrance, and the boundary layer continues to develop and thicken through the guide surface. At the same time, it can be seen that the side edges of the inlet induce vortices, and the side edge vortices gradually develop along the flow direction. After entering the inner channel, they gradually accumulate near the symmetry plane under the action of the lateral pressure gradient and the overall swirl, and finally there is a large range of low total pressure area dominated by vortices above the side of the outlet section.

[0026] like Figure 5 , Figure 7 and Figure 8 As shown, the embedded air inlet with a swept step in the present invention generates a strong local adverse pressure gradient due to the swept step facing the incoming flow. The existence of the lateral pressure gradient causes the low-energy fluid in the boundary layer to be diverted to the guide channel along the profile of the swept step, and then discharged out of the air inlet. Therefore, the boundary layer below the airflow entering the inner channel is relatively thin. In addition, due to the existence of the guide channel, the side edge vortex generated in this scheme is discharged out of the air inlet along the guide channel, so the low total pressure area above the outlet section is relatively small. Therefore, the total pressure recovery coefficient of the embedded air inlet based on the swept step to displace the forebody boundary layer is relatively large.

[0027] As shown in Table 1, the aerodynamic performance of the embedded air inlet with swept steps of the present invention is greatly improved compared with the baseline prototype embedded air inlet, and the total pressure recovery coefficient is improved by 2.1%.

[0028] Table 1 Performance comparison of conventional buried air inlet and buried air inlet of the present invention (simulation results)

[0029]

[0030] In addition, the present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be regarded as the scope of protection of the present invention.

Claims

1. A submerged air inlet based on a swept step to displace the forebody boundary layer, characterized in that: It includes an air inlet, a rear lip located at the rear end of the air inlet, a guide surface recessed inward from the air inlet, an inner channel formed by extending backward from the rear lip, and guide channel surfaces located on both sides of the rear lip, the inner channel includes an arc-shaped inner surface located in the rear lip, the two sides of the arc-shaped inner surface are respectively connected to the two sides of the rear lip to form an overall channel structure, and a swept line located at a relatively forward position of the front edge of the rear lip is formed by extending from the two sides of the rear lip to the middle, and a swept step surface is also provided between the swept line and the guide surface, the front edge of the swept step surface is connected to the guide surface, and the rear edge of the swept step surface is connected to the swept line; the swept step surface forms a swept extension from the middle to both sides until it is smoothly transitionally connected with the guide channel surfaces on both sides of the rear lip; The swept step has a width a, a height h, and a step sweep angle α, satisfying 0.40D≤a≤0.41D, 0.23D≤h≤0.24D, 30°≤α≤33°, where D is the inner channel diameter; The inlet of the air inlet is formed from the outer surface of the aircraft fuselage inward to form an embedded air inlet structure; the guide surface extends inwardly at an angle, the guide angle formed by the guide surface and the outer surface of the aircraft fuselage is 17°≤Ψ≤21°, and a transitional side edge is connected between the guide surface and the outer surface of the aircraft fuselage; The guide channel surface, the side edges and the outer side of the rear lip form a guide channel, the guide channel surface extends obliquely from the inside to the outside, and the guide channel surface is smoothly transitionally connected with the swept step surface at the inner end, and the guide channel surface is connected with the outer surface of the aircraft fuselage at the outer end. The leading edge width of the guide channel is z, satisfying 0.25D≤z≤0.26D.

2. The embedded air intake according to claim 1, characterized in that: The swept-back profile is a symmetrical profile, and a sharp point is formed at the front end of the swept-back profile, and an arc-shaped profile is extended from the sharp point to both sides; the profile of the leading edge of the swept-back step surface also forms a sharp point at the front end, and extends from the sharp point to both sides to form an arc-shaped symmetrical profile.

3. The embedded air intake according to claim 2, characterized in that: The front edge of the rear lip is swept back to both sides to form a horizontal "Λ" shape, and the rear lip sweep angle is β, which satisfies 33°≤β≤37°.

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