CN-115712953-B - S-bend stealth air inlet channel optimal design method based on inverted ray tracking

CN115712953BCN 115712953 BCN115712953 BCN 115712953BCN-115712953-B

Abstract

The invention relates to the technical field of aircraft air inlet channel design, and discloses an S-bend stealth air inlet channel optimization design method based on inverted ray tracing, which is based on the ray tracing principle, and by strong specular scattering echo of the air inlet channel outlet section, tracking the scattering position of the secondary scattering wave and the incident angle of the incident wave, and judging whether the strong scattering part needs to be optimized and coated with the wave absorbing material according to whether the incident angle is positioned in an important threat zone. The S-bend air inlet stealth design method comprehensively considers the strong scattering source distribution of the incident electromagnetic wave in any direction, and provides a direction for the optimal design of the stealth air inlet and the coating of the wave absorbing material.

Inventors

YU LONGZHOU
HUANG JIANGTAO
ZHONG SHIDONG
CHEN LILI
CHEN XIAN
CHEN CHENG
HE CHENGJUN
WANG YINZHU

Assignees

中国空气动力研究与发展中心空天技术研究所

Dates

Publication Date: 20260505
Application Date: 20221102

Claims (2)

1. An S-bend stealth air inlet channel optimization design method based on inverted ray tracking is characterized by comprising the following steps: S1, taking the center of a circle of an outlet of an air inlet as a coordinate origin, setting an axis which is perpendicular to the outlet of the air inlet and points to the inlet of the air inlet as an x axis, and setting an aircraft wing-span direction as a y axis in a circular port surface of the outlet of the air inlet to establish a coordinate system; S2, according to an electromagnetic propagation rule, setting the highest frequency of the stealth design of the air inlet channel as f, setting the wavelength as lambda at the interval of one fifth of the wavelength under the frequency, dividing the outlet of the air inlet channel with a circular section into N rows and N columns, wherein N=L/(lambda/5), L is the diameter of the circular section of the outlet of the air inlet channel, obtaining the nth row of the outlet of the air inlet channel, and the mth column dividing unit 4 is positioned in the nth row of the divided units, and the mth column has the central coordinate expressed as (0, y 0 (nm),z 0 (nm)); S3, setting the length from the inlet of the air inlet to the outlet of the air inlet as S, and obtaining a space description equation of the structure of the air inlet as follows: f(x,y,z),0≤x≤S (1) After the electromagnetic wave passes through the n rows and the center of the m column dividing unit, the scattered wave is a first scattered echo, the vector direction of the scattered wave is perpendicular to the outlet of the air inlet channel, and the expression is as follows: Wherein a 1 is a real number, b 1 ＝0,c 1 = 0; The linear equation of the first scattered echo can be obtained through the center of the nth row and mth column dividing unit 4 as follows: wherein k is a real number; S4, solving the combined type (1) and the formula (3) to obtain a coordinate (x 1 ,y 1 ,z 1 ) of a first scattering point, and further obtaining a normal vector of the first scattering point according to the formula (1) as follows: S5, according to the Snell theorem, after being scattered by the first scattering point, the vector of the second scattering echo The equation can be found as follows: And so on, obtaining the coordinates (x 2 ,y 2 ,z 2 ) of the second scattering point and passing through the normal vector of the second scattering point Third scatter echo vector And a linear equation, then sequentially obtaining the coordinates (x 3 ,y 3 ,z 3 ) of the third scattering point, and passing through the normal vector of the third scattering point 7 Vector of third scattered echo A straight line equation; s6, and so on, obtaining the vector of the nth scattered echo after passing through the nth scattering point (x n ,y n ,z n ) Vector passing through n-th scattering point (x n ,y n ,z n ) and n-th scattering echo And solving the linear equation of the nth scattered echo and the equation (1) simultaneously, wherein when the equation is not greater than x n , the equation is solved, which shows that the electromagnetic scattered echo has no intersection point with the air inlet channel structure equation, namely the electromagnetic scattered echo is incident into free space at the moment, and the expression of the included angle theta between the scattered echo and the x axis is as follows: if theta is more than 45 degrees, the electromagnetic wave is scattered to a non-key direction, and optimization is not needed, and if theta is less than 45 degrees, the structure of the air inlet channel is optimized.
2. The optimization design method of the S-bend stealth air inlet based on the backward ray tracing according to claim 1, wherein when θ <45 ° in the step S6, the specific method for optimization is to change the curvature of the air inlet tube so that the incident angle θ of the backward traced incident wave is greater than 45 °.

Description

S-bend stealth air inlet channel optimal design method based on inverted ray tracking Technical Field The invention relates to the technical field of aircraft air inlet channel design, in particular to an S-bend stealth air inlet channel optimal design method based on inverted ray tracking. Background With the rapid development of electronic technology, various target detection technologies form serious threat to the viability of the fighter aircraft on the battlefield, and stealth performance becomes an important index of the viability of the military aircraft, especially for the electromagnetic stealth performance of the radar working in the microwave band. The fighter aircraft pursues electromagnetic stealth capability at full frequency and full space, and the electromagnetic stealth capability within a forward + -45 DEG cone angle range is particularly interesting for the fighter aircraft. The cavity structure formed by the air inlet of the aircraft is the most main contribution source of the forward radar cross section of the aircraft, and incident waves are reflected for multiple times through the metal wall surface of the air inlet, and strong scattering echoes are formed in the inlet direction of the air inlet after being reflected by the metal blades of the compressor and the like. At present, two main design methods of the invisible air inlet are adopted, namely, S-bend design and double S-bend design are adopted, and wave absorbing materials are coated on the wall surface of the air inlet. Since specular scattering is a strong scattering source, its scattering intensity gradually decreases as the incident wave vector deviates from the specular normal. The basic principle of S-bend stealth air inlet channel design is that shielding of an air compressor blade is formed through the structure of the air inlet channel, so that plane electromagnetic waves entering in any (or key) direction are prevented from directly irradiating a metal plane, mirror scattering echoes are difficult to form on the air compressor blade, the incident waves form multiple scattering through an air inlet channel pipeline, and echo power along the direction of the incident waves is weakened. After scattering loss and metal wall ohmic loss, the secondary scattering wave formed by wall multiple scattering weakens electromagnetic wave power incident on the compressor blade to a certain extent, but still cannot be prevented from perpendicularly entering the compressor blade to form stronger scattering echo. The method of coating the wave-absorbing material is adopted, and electromagnetic wave energy is absorbed and converted into heat energy by means of dielectric loss or magnetic loss of the material so as to reduce the energy of scattered echo. For aircraft design, the wave absorbing material coating reduces the radar cross section of the air inlet channel, and simultaneously increases the burden of the structural weight of the aircraft. Therefore, in order to reduce the structural weight load of the wave-absorbing material, it is important to achieve a good wave-absorbing effect by reasonably arranging the coating positions of the wave-absorbing material and using as little wave-absorbing material as possible. In addition, under the incident condition of different spatial orientations, the distribution of the strong scattering areas of the air inlet channel cavity is different, so that how to globally grasp the distribution of the strong scattering sources of the air inlet channel cavity structure is particularly urgent, and guidance is provided for the coating of the wave absorbing material. Disclosure of Invention In order to overcome the defects in the prior art, the invention provides an S-bend stealth air inlet channel optimization design method based on inverted ray tracking, which is based on a ray tracking principle, tracks the scattering position of a secondary scattered wave and the incident angle of an incident wave through strong specular scattering echoes of the outlet section of the air inlet channel, and judges whether the strong scattering part needs to be optimized and coated with a wave absorbing material according to whether the incident angle is positioned in an important threat zone or not. The S-bend air inlet stealth design method comprehensively considers the strong scattering source distribution of the incident electromagnetic wave in any direction, and provides a direction for the optimal design of the stealth air inlet and the coating of the wave absorbing material. The technical aim of the invention is realized by the following technical scheme that the S-bend stealth air inlet channel optimization design method based on the inverted ray tracking comprises the following steps: S1, taking the center of a circle of an outlet of an air inlet as a coordinate origin, setting an axis which is perpendicular to the outlet of the air inlet and points to the inlet of the air inlet as an x axis, and setting an