A semi-buried air intake with steps

Abstract

The present invention provides a stepped semi-submerged air inlet, comprising an air inlet inner channel, a first air inlet guide surface, a second air inlet guide surface extending forward of the first air inlet guide surface, and a stepped portion higher than the second air inlet guide surface. By setting the height of the upper surface of the stepped portion to be the same as the height of the upper surface of the lip shield, the air inlet port has no additional orthographic projection area, thereby improving stealth performance and reducing headwind resistance. By providing a groove in the stepped portion that gradually expands from front to rear and to both sides, and forming a swept-back triangular wedge higher than the second air inlet guide surface at the junction of the front end of the first air inlet guide surface and the second air inlet guide surface, high-quality incoming flow at the air inlet is ensured.

Description

Technical Field

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

[0002] Subsonic aircraft are currently the most widely used type of air-breathing aircraft, and missiles are one of their primary applications. Subsonic aircraft power systems typically utilize three types of inlets: 1. Pitot-type inlet; 2. S-bend inlet; and 3. Submerged inlet.

[0003] As the overall design of aircraft puts forward higher requirements for the additional resistance of subsonic air inlets and radar stealth performance, the Pitot-type air inlet is becoming increasingly difficult to meet the requirements. This has also led to the widespread use of S-shaped air inlets and buried air inlets.

[0004] In subsonic aircraft, conventional S-bend inlets have good aerodynamic performance, but their stealth effect is poor. Compared with embedded inlets, conventional S-bend inlets have a significant orthographic projection area (abbreviated as orthographic projection area), which easily generates strong radar reflection waves. At the same time, the orthographic projection area inevitably brings corresponding wind resistance. Embedded inlets have no orthographic projection area, and have higher stealth performance and lower wind resistance, but have poor aerodynamic performance. Therefore, there is an urgent need to develop a new type of inlet that combines the advantages of S-bend inlets and embedded inlets, so that it has both good aerodynamic performance and good stealth characteristics.

[0005] Please combine Figure 1 、 Figure 2 The figure shows an S-bend inlet in the prior art. An S-bend inlet is an inlet with an S-shaped internal duct. It efficiently converts airflow kinetic energy into pressure energy through the ramming effect of high-speed incoming airflow. Subsonic aircraft that commonly use piggyback S-bend inlets require a boundary layer separator to partially or completely remove the boundary layer that develops along the fuselage in order to reduce the interference of the boundary layer at the inlet inlet on the flow within the inlet duct. This means that the air inlet must be raised a certain height from the fuselage surface. Consequently, the S-bend inlet has a positive projection area, resulting in poor stealth performance and high headwind drag.

[0006] Please combine Figure 3 、 Figure 4The figure shows a prior art embedded air inlet. This type of inlet is a subsonic air inlet that integrates the inlet with the fuselage surface and buries the air intake duct within the fuselage, without any protrusions on the fuselage surface. Because it has no orthographic projection area, it offers advantages such as low headwind resistance and good stealth performance, and is convenient for missile box-type launches. However, common embedded air inlets are completely unable to utilize the ramjet effect of incoming airflow for intake, and it is difficult to install boundary layer separators similar to those in S-bend air inlets. This causes a large amount of boundary layer developing along the fuselage to be entrained into the inner flow channel, resulting in low performance of the embedded air inlet. Currently, to improve the performance of embedded air inlets for missiles, mechanical vortex generators are often used. While this can effectively increase the total pressure recovery coefficient and reduce the total pressure distortion at the outlet, the vortex generators not only introduce significant additional drag but also pose a risk of detachment.

[0007] Therefore, the S-curved air inlet has high aerodynamic performance but poor stealth performance, while the buried air inlet has good stealth performance but poor aerodynamic performance.

[0008] Please combine Figure 5 、 Figure 6 As shown, there are currently studies on semi-submerged air inlets. The design principle is to combine submerged air inlets with S-bend air inlets in an attempt to reconcile the incompatible contradiction between "aerodynamic performance" and "stealth performance". The specific implementation method is to add a lip protruding from the fuselage or the body of the aircraft to the submerged air inlet. This not only reduces the orthographic projection area compared to conventional S-bend air inlets, but also can simultaneously utilize the side vortex of the submerged air inlet and the high-speed airflow ramjet effect of the S-bend air inlet to achieve air intake.

[0009] Obviously, this type of semi-submerged inlet still has a positive projection area, and its protruding surface still causes headwind resistance. Therefore, the two major goals of "reducing the positive projection area to zero" and "improving intake efficiency" are not completely achieved simultaneously. Moreover, this inlet solution is not conducive to the storage of missiles in launch boxes. In addition, this type of semi-submerged inlet cannot be equipped with a boundary layer separator, so it will still inhale a large amount of boundary layer developed from the fuselage, resulting in poor aerodynamic performance. If you want to improve performance, you still face the various additional disadvantages brought by the use of mechanical vortex generators, just like the submerged inlet. Summary of the Invention

[0010] To solve the above problems, the present invention provides a semi-buried air inlet with steps, the purpose of which is to reduce the headwind resistance of the aircraft, improve the radar stealth performance of the aircraft, and effectively improve the total pressure recovery coefficient and flow field distortion index of the air inlet.

[0011] To achieve the above-mentioned purpose, the semi-buried air inlet with steps provided by the present invention can adopt the following technical solutions:

[0012] A semi-submerged air intake with a step, comprising an air intake inner wall, side walls located on both sides of the air intake inner wall, and lip covers located on the side walls. The air intake inner wall, the lip covers, and the side walls on both sides together form an inner air intake passage. A first air intake guide surface and a second air intake guide surface extending forward from the first air intake guide surface are provided at the entrance of the inner air intake passage. A step portion higher than the second air intake guide surface is provided in front of the second air intake guide surface. The height of the upper surface of the step portion is the same as the height of the upper surface of the lip cover.

[0013] The step portion is provided with a groove that gradually expands from front to back and to both sides, with the front vertex of the groove located at the center of the width of the step portion, and the rear end of the groove forming an expanded opening so that the bottom surface of the rear end of the groove and the second air inlet guide surface are located in the same plane;

[0014] A swept-back triangular wedge is formed at the junction of the front end of the first air inlet duct guide surface and the second air inlet duct guide surface, and the front end of the swept-back triangular wedge is a tip and extends obliquely backward from the tip to form an edge that is higher than the second air inlet duct guide surface.

[0015] Furthermore, the front bottom surface of the groove is at the same height as the step portion at the vertex, and the front bottom surface of the groove gradually sinks downward from the vertex so that the front bottom surface of the groove forms a slope that gradually sinks from front to back.

[0016] Furthermore, the two side surfaces of the groove are arc-shaped surfaces that gradually expand outward, and the arc-shaped surfaces on both sides are symmetrically arranged.

[0017] Furthermore, the height of the step portion is higher than the height of the first air inlet duct guide surface.

[0018] Furthermore, the first air inlet guide surface is an arc-shaped surface extending and tilting downward from front to rear.

[0019] Furthermore, the inner channel of the air intake duct is an S-shaped inner channel of the air intake duct.

[0020] Furthermore, a line connecting the front vertex of the groove and the tip of the swept-back triangular wedge coincides with a longitudinal section where the central axis of the inner channel of the air inlet is located.

[0021] Furthermore, the grooves and the swept-back triangular wedges are used to remove the boundary layer to both sides of the inlet.

[0022] Furthermore, the front end of the lip cover is triangular in shape so that the air inlet entrance is swept back.

[0023] Furthermore, the step portion is a part of the aircraft fuselage.

[0024] Beneficial Effects: The present invention utilizes a structure in which both sides of the groove gradually expand outward, thereby generating vortices directed toward both sides of the second air inlet guide surface. This effectively removes the boundary layer formed by the step portion, as well as the boundary layer thickening or separation that may occur naturally due to the height difference between the step portion and the second air inlet guide surface, toward both sides of the second air inlet guide surface, thereby providing uniform, high-quality airflow for the semi-submerged air inlet. The swept-back triangular wedge and the groove jointly eliminate the air inlet boundary layer, ensuring high-quality incoming flow at the air inlet. Furthermore, the height of the upper surface of the step portion is the same as that of the upper surface of the lip shield, so that in the rearward projection angle from the aircraft's head, the air inlet does not appear in this projection angle due to the full shielding of the step portion. That is, the air inlet has no additional positive projection area, thereby improving stealth performance and reducing headwind drag. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a cross-sectional view of an S-bend air inlet in the prior art.

[0026] Figure 2 It is an axonometric diagram of an S-bend air inlet in the prior art.

[0027] Figure 3 It is an axonometric diagram of a buried air intake in the prior art.

[0028] Figure 4 It is a cross-sectional view of a buried air inlet in the prior art.

[0029] Figure 5 It is an axonometric diagram of a semi-buried air intake in the prior art.

[0030] Figure 6 It is a cross-sectional view of a semi-buried air intake in the prior art.

[0031] Figure 7 It is a simulation model diagram of the semi-buried air inlet with steps of the present invention.

[0032] Figure 8 It is an axonometric view of the semi-buried air inlet with steps of the present invention.

[0033] Figure 9 It is a cross-sectional view of the semi-buried air inlet with steps of the present invention.

[0034] Figure 10 It is a top view of the semi-buried air inlet with steps of the present invention.

[0035] Figure 11 This is a velocity distribution cloud diagram on the symmetry surface obtained by simulating the semi-buried air inlet with steps of the present invention.

[0036] Figure 12This is a three-dimensional streamline diagram obtained by simulating the semi-buried air inlet with steps of the present invention and emitted at a position 1 mm away from the body wall.

[0037] Figure 13 The three-dimensional streamline diagram emitted from the airframe wall is obtained by simulating the semi-buried air inlet with steps of the present invention.

[0038] Figure 14 This is a map of the total pressure recovery coefficient at the inlet outlet obtained by simulating the semi-buried inlet with steps of the present invention. DETAILED DESCRIPTION

[0039] See also Figures 7 to 10 As shown, a stepped, semi-submerged air inlet comprises an air inlet inner wall 8, sidewalls 5 located on either side of the air inlet inner wall, and lip shields 3 located on the sidewalls. The air inlet inner wall 8, lip shield 3, and sidewalls 5 together form an air inlet inner channel 4. In this embodiment, the air inlet inner channel 4 is in the form of a conventional S-bend air inlet inner pipe, so that the air inlet inner channel 4 is buried within the aircraft body when extended rearward. The front end of the lip shield 3 is triangular in shape, giving the air inlet entrance a swept-back shape, and the air inlet lip also forms a swept-back shape. The sweep angle of the air inlet lip is determined according to the application scenario, and different sweep angles can be used on different aircraft to enhance the stealth performance of the air inlet.

[0040] Extending forward from the inlet channel entrance is a first inlet guide surface 6 and a second inlet guide surface 2 extending forward from the first inlet guide surface 6. A step 7, higher than the second inlet guide surface 2, is located in front of the second inlet guide surface 2. Specifically, the step 7 is higher than the first inlet guide surface 6. A recessed groove 10 is formed in the step 7, gradually expanding from front to back and to both sides. The front end apex of the groove 10 is located at the center of the width of the step 7. The rear end of the groove 10 forms an expanded opening 12, aligning the bottom surface of the rear end of the groove 10 with the second inlet guide surface 2. Furthermore, a swept-back triangular wedge 11, higher than the second inlet guide surface 2, is formed at the junction of the front end of the first inlet guide surface 6 and the second inlet guide surface 2. The swept-back triangular wedge 11 has a pointed tip, and an edge 12 extends obliquely backward from the tip, extending higher than the second inlet guide surface 2.

[0041] In order to achieve full shielding of the semi-buried air inlet duct air inlet 1, that is, there is no additional orthographic projection area, in this embodiment, the height of the upper surface of the step portion 7 is made the same as the height of the upper surface of the lip cover 3, so that in the projection angle from the head of the aircraft to the rear, the air inlet 1 will not appear in the projection angle due to the full shielding of the step portion 7, that is, the air inlet 1 has no additional orthographic projection area, thereby improving the stealth performance and reducing the windward resistance.

[0042] Combine Figure 9 As shown in FIG, the front bottom surface of the groove 10 is at the same height as the step 7 at the vertex position, and the front bottom surface of the groove 10 gradually sinks downward from the vertex, forming a slope that gradually sinks from front to back. In this embodiment, the slope is slightly curved. The two side surfaces of the groove 10 are curved surfaces that gradually expand outward until they expand into the opening 12, and the curved surfaces on both sides are symmetrically arranged.

[0043] In addition, the first air inlet guide surface 6 is an arc-shaped surface extending downward from front to rear. That is, the air inlet 1 uses the ram pressure of the incoming flow to intake air through the downward-sloping first air inlet guide surface 6, giving the semi-submerged air inlet the characteristics of an S-bend air inlet. Furthermore, the bottom edge of the air inlet 1 and the first air inlet guide surface 6 are completely aligned, and there is no boundary layer partition found in existing S-bend air inlets. This can effectively reduce the aerodynamic drag of the aircraft while avoiding the strong radar scattering echo caused by the presence of boundary layer partitions. The air inlet inner channel 4 adopts the form of a conventional S-bend air inlet inner pipe, thereby improving the performance parameters of the semi-submerged air inlet and effectively improving the total pressure recovery coefficient and total pressure distortion index.

[0044] The line connecting the front vertex of the groove 10 and the tip of the swept-back triangular wedge 11 coincides with the longitudinal section of the central axis of the inlet passage. The groove 10 and the swept-back triangular wedge 11 are used to displace the boundary layer toward the sides of the inlet. The gradually outward-expanding sides of the groove 10 generate vortices directed toward the sides of the second inlet guide surface 2. This effectively displaces the boundary layer formed by the step 7, as well as the boundary layer thickening or potential separation naturally caused by the height difference between the step 7 and the second inlet guide surface 2, toward the sides of the second inlet guide surface 2, thereby providing uniform, high-quality airflow for the semi-submerged inlet 1. The swept-back triangular wedge 11 is placed on the second inlet guide surface 2. Through the two swept-back surfaces of the triangular wedge 6, it naturally displaces the boundary layer on the second inlet guide surface 2 toward the sides of the inlet sidewall 5. Its height and sweep angle can be determined based on the development of the boundary layer. The swept-back triangular wedge 6 and the groove 10 together eliminate the boundary layer of the air inlet, thereby ensuring high-quality incoming flow at the air inlet 1.

[0045] Please combine Figure 11 、 Figure 12 、 Figure 13 The figure shows the simulation verification of the semi-buried air inlet with steps described in this embodiment. Figure 11As can be seen in the figure, the boundary layer on the second air inlet guide surface 2 develops into the boundary layer on the first air inlet guide surface 6 after the action of the swept-back triangular wedge 11. The boundary layer on the first air inlet guide surface 6 is significantly thinner than the boundary layer on the second air inlet guide surface 2, thus ensuring the flow field quality at the air inlet 1. In addition, Figure 12 As can be seen in Figure 13, the vortex induced by the step portion can move the low-energy flow upstream of the inlet to both sides, thereby achieving the desired effect of eliminating the boundary layer of the inlet. Figure 14 It can be seen that through the analysis of the inlet outlet map, at the inlet Mach number of 0.7, the angle of attack of 2°, and the outlet Mach number of 0.57, the total pressure recovery coefficient of the inlet outlet reaches 0.96, which is significantly higher than the performance of the conventional embedded inlet under the same working conditions.

Claims

1. A semi-submerged air intake with a step, comprising an air intake inner wall, side walls located on both sides of the air intake inner wall, and lip covers located on both side walls, wherein the air intake inner wall, the lip covers, and the side walls on both sides together form an inner channel of the air intake; characterized in that: A first air inlet guide surface (6) and a second air inlet guide surface (2) extending forward from the first air inlet guide surface (6) are provided at the entrance of the air inlet channel. A step portion (7) higher than the second air inlet guide surface (2) is provided in front of the second air inlet guide surface (2); the height of the upper surface of the step portion (7) is the same as the height of the upper surface of the lip mask; The step portion (7) is provided with a groove (10) that gradually expands from the front to the rear and to both sides, the front end vertex of the groove (10) is located at the center of the width of the step portion, and the rear end of the groove forms an expanded opening so that the bottom surface of the rear end of the groove and the second air inlet guide surface (2) are located in the same plane; the height of the step portion (7) is higher than the height of the first air inlet guide surface (6); A swept-back triangular wedge (11) is formed at the junction of the front end of the first air inlet duct guide surface (6) and the second air inlet duct guide surface (2), and the swept-back triangular wedge (11) is higher than the second air inlet duct guide surface (2). The front end of the swept-back triangular wedge (11) is a tip, and an edge (12) extends obliquely backward from the tip and is higher than the second air inlet duct guide surface (2).

2. The stepped semi-submerged air intake according to claim 1, characterized in that: The front end bottom surface of the groove (10) is at the same height as the step portion (7) at the vertex position, and the front end bottom surface of the groove (10) gradually sinks downward from the vertex so that the front end bottom surface of the groove (10) forms an inclined surface that gradually sinks from front to back.

3. The stepped semi-buried air inlet according to claim 1 or 2, characterized in that: The two side surfaces of the groove (10) are arc-shaped surfaces that gradually expand outwards, and the arc-shaped surfaces on both sides are symmetrically arranged.

4. The stepped semi-submerged air intake according to claim 1, characterized in that: The first air inlet guide surface (6) is an arc-shaped surface extending from front to back and tilting downward.

5. The stepped semi-submerged air inlet according to claim 1, characterized in that: The inner channel of the air intake duct is an S-shaped inner channel of the air intake duct.

6. The stepped semi-submerged air intake according to claim 4, characterized in that: The line connecting the front vertex of the groove (10) and the tip of the swept-back triangular wedge (11) coincides with the longitudinal section of the central axis of the air inlet channel.

7. The stepped semi-submerged air inlet according to claim 6, characterized in that: The groove (10) and the swept-back triangular wedge (11) are used to exclude the boundary layer to both sides of the inlet.

8. The stepped semi-submerged air intake according to claim 1, characterized in that: The front end of the lip cover is triangular in shape, so that the inlet of the air inlet is swept back.

9. The stepped semi-submerged air intake according to claim 1, characterized in that: The step portion (7) is a part of the aircraft fuselage.

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