An Optimization Design Method for S-Bend Stealth Inlet Based on Inverse Ray Tracing

Abstract

This invention relates to the field of aircraft air intake design technology, and discloses an optimization design method for an S-curve stealth air intake based on reverse ray tracing. Based on the principle of ray tracing, the scattering position of the secondary scattered wave and the incident angle of the incident wave are tracked by the strong specular scattering echo from the air intake outlet section. The method determines whether the strong scattering area needs optimization and radar-absorbing material coating based on whether the incident angle is located in a critical threat zone. This S-curve air intake stealth design method comprehensively considers the distribution of strong scattering sources of electromagnetic waves incident from any direction, providing direction for the optimization design of stealth air intakes and the coating of radar-absorbing materials.

Description

Technical Field

[0001] This invention relates to the field of aircraft air intake design technology, and more specifically, to an optimization design method for S-curve stealth air intakes based on reverse ray tracing. Background Technology

[0002] With the rapid development of electronic technology, various target detection technologies have posed a serious threat to the survivability of combat aircraft on the battlefield. Stealth performance has become an important indicator of the survivability of military aircraft, especially electromagnetic stealth performance for radars operating in the microwave band. Combat aircraft pursue full-frequency, all-space electromagnetic stealth capabilities, and for combat aircraft, their electromagnetic stealth capabilities within a forward ±45° cone angle range are particularly noteworthy. The cavity structure formed by the aircraft's air intake is the primary contributor to the aircraft's forward radar cross-section. Incident waves undergo multiple reflections through the metal walls of the air intake, and after reflections by the compressor's metal blades, a strong scattered echo is formed in the direction of the air intake inlet.

[0003] Currently, there are two main design methods for stealth air intakes: one is to use an S-bend or double S-bend design, and the other is to coat the intake wall with radar-absorbing materials. Since specular scattering is a strong scattering source, its scattering intensity gradually weakens as the incident wave vector deviates from the normal to the specular surface. The basic principle of the S-bend stealth air intake design is to use the intake structure itself to shield the compressor blades, thereby preventing plane electromagnetic waves incident from any (or critical) direction from directly irradiating the metal surface. This makes it difficult for them to form specular scattering echoes on the compressor blades. The incident wave undergoes multiple scatterings through the intake duct, weakening the echo power along the incident wave direction. The secondary scattered waves formed after multiple scatterings on the wall, after scattering loss and ohmic loss of the metal wall, although weakening the electromagnetic wave power incident on the compressor blades to some extent, still cannot prevent the secondary scattered waves from perpendicularly incident on the compressor blades and forming strong scattered echoes. The method of coating with radar-absorbing materials reduces the energy of the scattered echoes by absorbing electromagnetic wave energy and converting it into heat energy through the dielectric or magnetic loss of the material. For aircraft design, while radar-absorbing material coating reduces the radar cross-section of the air intake, it also increases the structural weight of the aircraft. Therefore, to mitigate the structural weight burden caused by radar-absorbing materials, it is crucial to rationally plan the coating locations and achieve optimal absorption with minimal material. Furthermore, since the distribution of strong scattering regions within the air intake cavity varies depending on the incident spatial orientation, understanding the overall distribution of strong scattering sources within the air intake cavity structure is essential for guiding the application of radar-absorbing materials. Summary of the Invention

[0004] To overcome the aforementioned deficiencies in existing technologies, this invention provides an S-bend stealth air intake optimization design method based on reverse ray tracing. Based on the principle of ray tracing, the scattering position of the secondary scattered wave and the incident angle of the incident wave are tracked through the strong specular scattering echo from the air intake outlet section. Whether the incident angle is located in a critical threat zone is used to determine whether optimization and coating with absorbing materials are necessary for the strong scattering areas. This S-bend air intake stealth design method comprehensively considers the distribution of strong scattering sources of electromagnetic waves incident from any direction, providing direction for the optimization design of stealth air intakes and the coating of absorbing materials.

[0005] The above-mentioned technical objective of this invention is achieved through the following technical solution: an optimization design method for an S-curve stealth air intake based on reverse ray tracing, comprising the following steps:

[0006] S1. With the center of the air intake outlet as the origin of the coordinate system, let the axis perpendicular to the air intake outlet and pointing towards the air intake inlet be the x-axis, and let the wingspan direction of the aircraft be the y-axis within the circular opening of the air intake outlet.

[0007] S2. According to the electromagnetic propagation law, let the highest frequency of the stealth design of the air intake be f. With one-fifth of the wavelength at this frequency as the interval, let the wavelength be λ. Divide the circular cross-section of the air intake outlet into N rows and N columns, N=L / (λ / 5), where L is the diameter of the circular cross-section of the air intake outlet. It is found that the nth row and mth column of the air intake outlet segment 4 is located in the nth row and mth column of the segmented unit, and its center coordinates are represented as (0, y0(nm), z0(nm)).

[0008] S3. Let S be the length from the intake duct inlet 1 to the intake duct outlet. The spatial description equation of the intake duct structure is as follows:

[0009] f(x, y, z), 0 ≤ x ≤ S (1)

[0010] After the electromagnetic wave passes through the center of the segmented unit in the nth row and mth column, the scattered wave is the first scattered echo, whose vector direction is perpendicular to the air intake outlet, as expressed below:

[0011]

[0012] Where a1 is a real number, b1 = 0, c1 = 0;

[0013] The linear equation of the first scattered echo can be obtained by passing through the center of the nth row and mth column segment 4 as follows:

[0014]

[0015] Where k is a real number.

[0016] S4. Solving equations (1) and (3) simultaneously, we obtain the coordinates of the first scattering point as (x1, y1, z1). Based on equation (1), we further obtain the normal vector passing through the first scattering point as shown below:

[0017]

[0018] S5. According to Snell's theorem, after scattering at the first scattering point, the vector of the second scattered echo... It can be obtained through the following equation:

[0019]

[0020] By analogy, the coordinates (x2, y2, z2) of the second scattering point are obtained, and the normal vector passing through the second scattering point is also calculated. Third scattered echo vector And the equation of the line; then, the coordinates (x3, y3, z3) of the third scattering point are obtained in sequence, and the normal vector passing through the third scattering point 7 is obtained. The vector of the third scattered echo and the equation of the straight line;

[0021] S6. Following this pattern, we can obtain the scattering point (x) after passing through the nth scattering point. n ,y n ,z n After that, the vector of the nth scattered echo. Through the nth scattering point (x) n ,y n ,z n The vector of the nth scattered echo. The linear equation of the nth scattered echo can then be obtained. By simultaneously solving the linear equation of the nth scattered echo and equation (1), when there is no value greater than x in the solution... n When the solution is obtained, it indicates that the electromagnetic scattered echo has no intersection with the intake duct structural equations. That is, the electromagnetic scattered echo is incident on free space. The expression for the angle θ between the scattered echo and the x-axis is as follows:

[0022]

[0023] If θ > 45°, it means that the electromagnetic waves are scattered to non-critical directions and no optimization is needed; if θ < 45°, it means that the electromagnetic waves are scattered to the spatial orientation that the stealth design of the air intake is focused on, and the air intake duct structure needs to be optimized.

[0024] Furthermore, when θ < 45° as mentioned in step S6, the specific optimization method is to change the curvature of the air intake pipe shape so that the incident angle θ of the reverse-tracked incident wave is > 45°, so that the reverse-tracked incident wave deviates from the spatial orientation that the air intake stealth design focuses on.

[0025] In summary, this invention has the following beneficial effects: Based on the principle of ray tracing, this invention tracks the scattering position of the secondary scattered wave and the incident angle of the incident wave by using the strong specular scattering echo from the air intake outlet section. It then determines whether the strong scattering area needs optimization and the application of absorbing materials based on whether the incident angle is located in a critical threat zone. The S-curve air intake stealth design method comprehensively considers the distribution of strong scattering sources of electromagnetic waves incident from any direction, providing direction for the optimized design of stealth air intakes and the application of absorbing materials. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the S-curve air intake structure in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the spatial segmentation method for the surface of the compressor blade in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the reverse ray tracing process inside the air intake in an embodiment of the present invention. Detailed Implementation

[0029] The following is in conjunction with the appendix Figure 1-3 The present invention will be described in further detail below.

[0030] Example: An optimization design method for S-curve stealth air intakes based on inverse ray tracing, such as... Figures 1 to 3 As shown, it includes the following steps:

[0031] S1. With the center of the air intake outlet as the origin of the coordinate system, let the axis perpendicular to the air intake outlet and pointing towards the air intake inlet be the x-axis, and let the wingspan direction of the aircraft be the y-axis within the circular opening of the air intake outlet.

[0032] S2. According to the electromagnetic propagation law, let f be the highest frequency used in the electromagnetic countermeasures of the air intake stealth design. Let λ be the wavelength at one-fifth of the wavelength at this frequency. Divide the circular cross-section of the air intake outlet into N rows and N columns, N = L / (λ / 5), where L is the diameter of the circular cross-section of the air intake outlet. It is found that the nth row and mth column dividing unit 4 of the air intake outlet is located in the nth row and mth column of the divided unit, and its center coordinates are represented as (0, y0(nm), z0(nm)).

[0033] S3. Let S be the length from the intake duct inlet 1 to the intake duct outlet. The spatial description equation of the intake duct structure is as follows:

[0034] f(x, y, z), 0 ≤ x ≤ S (1)

[0035] After the electromagnetic wave passes through the center of the segmented unit in the nth row and mth column, the scattered wave is the first scattered echo, whose vector direction is perpendicular to the air intake outlet, as expressed below:

[0036]

[0037] Where a1 is a real number, b1 = 0, c1 = 0;

[0038] The linear equation of the first scattered echo can be obtained by passing through the center of the nth row and mth column segment 4 as follows:

[0039]

[0040] Where k is a real number.

[0041] S4. Solving equations (1) and (3) simultaneously, we obtain the coordinates of the first scattering point as (x1, y1, z1). Based on equation (1), we further obtain the normal vector passing through the first scattering point as shown below:

[0042]

[0043] S5. According to Snell's theorem (the incident wave and the scattered wave are in the same plane and are uniformly distributed on both sides of the incident wave), after being scattered by the first scattering point, the vector of the second scattered echo is... It can be obtained through the following equation:

[0044]

[0045] By analogy, the coordinates (x2, y2, z2) of the second scattering point are obtained, and the normal vector passing through the second scattering point is also calculated. Third scattered echo vector And the equation of the line; then, the coordinates (x3, y3, z3) of the third scattering point are obtained in sequence, and the normal vector passing through the third scattering point 7 is obtained. The vector of the third scattered echo and the equation of the straight line;

[0046] S6. Following this pattern, we can obtain the scattering point (x) after passing through the nth scattering point. n ,y n ,z n After that, the vector of the nth scattered echo. Through the nth scattering point (x) n ,y n ,z n The vector of the nth scattered echo. The linear equation of the nth scattered echo can then be obtained. By simultaneously solving the linear equation of the nth scattered echo and equation (1), when there is no value greater than x in the solution... nWhen the solution is obtained, it indicates that the electromagnetic scattered echo has no intersection with the intake duct structural equations. That is, the electromagnetic scattered echo is incident on free space. The expression for the angle θ between the scattered echo and the x-axis is as follows:

[0047]

[0048] If θ > 45°, it means that the electromagnetic wave is scattered to a non-critical direction and no optimization is needed; if θ < 45°, the intake duct structure needs to be optimized. The specific optimization method is to change the curvature of the intake duct so that the incident angle θ of the incident wave tracked in reverse is > 45°.

[0049] like Figure 1 The diagram shows the structure of the S-curve air intake, where 1 is the air intake inlet, 2 is the air intake outlet, and 3 is the air intake pipe. The air intake outlet 3 is connected to the surface of the compressor blades, where electromagnetic waves are reflected.

[0050] like Figure 2 The diagram shows a spatial division method for the surface of a compressor blade, where 4 is the division unit in the nth row (1≤n≤N) and mth column (1≤m≤M) of the inlet outlet.

[0051] like Figure 3 The diagram illustrates the reverse ray tracing process within the air intake. Point 5 is the first scattering point 5 in the nth row and mth column of segmentation unit 4; point 6 is the second scattering point; point 7 is the third scattering point; point 8 is the first scattered echo; point 9 is the second scattered echo; point 10 is the third scattered echo; and point 11 is the fourth scattered echo. For electromagnetic waves scattered into free space, we primarily focus on echoes whose angle with S1 is less than 45°. The locations of all scattering points obtained using the aforementioned method are considered strong scattering points. Therefore, these strong scattering points can be identified using the aforementioned method, and electromagnetic scattering can be reduced by coating these locations with absorbing material. The above method can accurately locate the strong scattering points, thus providing direction for coating the S-bend stealth air intake with absorbing material.

[0052] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for optimizing the design of an S-curve stealth air intake based on inverse ray tracing, characterized in that, Includes the following steps: S1. With the center of the air intake outlet as the origin of the coordinate system, let the axis perpendicular to the air intake outlet and pointing towards the air intake inlet be the x-axis, and let the wingspan direction of the aircraft be the y-axis within the circular opening of the air intake outlet. S2. According to the electromagnetic propagation law, let the highest frequency of the air intake stealth design be f. With one-fifth of the wavelength at this frequency as the interval, let the wavelength be λ. Divide the circular cross-section of the air intake outlet into N rows and N columns, N=L / (λ / 5), where L is the diameter of the circular cross-section of the air intake outlet. It is found that the nth row and mth column dividing unit 4 of the air intake outlet is located in the nth row and mth column of the divided unit, and its center coordinates are represented as (0, y0(nm), z0(nm)). S3. Let S be the length from the intake duct inlet to the intake duct outlet. The spatial description equation of the intake duct structure is as follows: f(x, y, z), 0 ≤ x ≤ S (1) After the electromagnetic wave passes through the center of the segmented unit in the nth row and mth column, the scattered wave is the first scattered echo, whose vector direction is perpendicular to the air intake outlet, as expressed below: Where a1 is a real number, b1 = 0, c1 = 0; The linear equation of the first scattered echo can be obtained by passing through the center of the nth row and mth column segment 4 as follows: Where k is a real number; S4. Solving equations (1) and (3) simultaneously, we obtain the coordinates of the first scattering point as (x1, y1, z1). Based on equation (1), we further obtain the normal vector passing through the first scattering point as shown below: S5. According to Snell's theorem, after scattering at the first scattering point, the vector of the second scattered echo... It can be obtained through the following equation: By analogy, the coordinates (x2, y2, z2) of the second scattering point are obtained, and the normal vector passing through the second scattering point is also calculated. Third scattered echo vector And the equation of the line; then, the coordinates (x3, y3, z3) of the third scattering point are obtained in sequence, and the normal vector passing through the third scattering point 7 is obtained. The vector of the third scattered echo and the equation of the straight line; S6. Following this pattern, we can obtain the scattering point (x) after passing through the nth scattering point. n ,y n ,z n After that, the vector of the nth scattered echo. Through the nth scattering point (x) n ,y n ,z n The vector of the nth scattered echo. The linear equation of the nth scattered echo can then be obtained; by simultaneously solving the linear equation of the nth scattered echo and equation (1), when there is no value greater than x in the solution of the equation... n When the solution is obtained, it indicates that the electromagnetic scattered echo has no intersection with the intake duct structural equations. That is, the electromagnetic scattered echo is incident on free space. The expression for the angle θ between the scattered echo and the x-axis is as follows: If θ > 45°, it means that the electromagnetic waves are scattered to non-critical directions and no optimization is needed; if θ < 45°, the intake duct structure needs to be optimized.

2. The method for optimizing the design of an S-curve stealth air intake based on reverse ray tracing as described in claim 1, characterized in that, When θ < 45° as mentioned in step S6, the specific method for optimization is to change the curvature of the intake pipe shape so that the incident angle θ of the incident wave tracked in reverse is > 45°.

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