Method for simulating, predicting and measuring a shock field of an aircraft

Abstract

A simulation, prediction and measurement method of aircraft shock wave field, which analyzes the spectral characteristics of aircraft shock wave field, uses acoustic horn antenna to simulate the physical characteristics of shock wave field, and predicts the radar cross section (RCS) under the Bragg matching condition, uses high-power radar to detect at the Bragg matching frequency, obtains characteristic quantities such as power spectrum, RCS and frequency shift, can directly reflect the physical scattering process of atmospheric acoustic field, is easy to understand, provides a principle verification method for the outflow field detection of supersonic aircraft, and is suitable for electromagnetic scattering detection of atmospheric flow field.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic scattering testing, and more particularly to a method for simulating, predicting, and measuring shock fields of aircraft. Background Technology

[0002] When an aircraft cruises at supersonic speeds, its various components and engine plumes generate strong disturbances in the surrounding air, creating a series of shock wave systems and expansion wave systems. As these wave systems propagate toward the ground, they interact with each other, eventually forming two shock waves at the ground. When these shock waves sweep across the ground, observers hear a sound similar to an explosion, hence the term "sonic boom."

[0003] The generation of sonic booms from supersonic aircraft is closely related to volume and lift. When an aircraft flies at supersonic speeds through still air, fluid particles in the air do not receive disturbance signals and collide with the oncoming aircraft, causing displacement. These particles accumulate on the leading edge surface of the aircraft and are forced to move, accompanied by a sudden increase in density, temperature, and pressure, forming a shock wave system. Conversely, when moving on concave surfaces, the situation is exactly the opposite, forming an expansion wave system. Generally, the lower surface of the aircraft is a high-pressure region, composed of shock waves; the upper surface is a low-pressure region, composed of expansion waves.

[0004] Shock waves and expansion waves propagate at the local sound speed along their respective back Mach cone directions. The waveforms are distorted during propagation. The gas temperature where the shock wave is located is high, resulting in a fast propagation speed and a large propagation angle. Weak shock waves are swallowed up to form strong shock waves. Upon propagating to the far field, the wave system converges to both sides, forming an N-type wave. The "far field" is the region where the wave system evolution is essentially complete, and the sonic boom signal morphology does not change significantly. Generally, the ground falls into this category.

[0005] Among the publicly available and limitedly published literature retrieved both domestically and internationally, some papers proposed two-dimensional calculation formats for two-dimensional atmospheric medium changes, but none proposed calculation methods or simulation testing techniques for three-dimensional changing media. Other papers proposed high-oscillation integral calculation methods for the scattering characteristics of arbitrarily continuously changing media. Still other papers only proposed specific calculation methods for special change forms, failing to address the problem of coherent electromagnetic scattering testing for arbitrarily and continuously changing low-scattering media. Furthermore, no publicly available literature discloses radar coherent detection simulation testing techniques for aircraft shock fields. Summary of the Invention

[0006] The purpose of this invention is to provide a method for simulating, predicting, and measuring the shock field of an aircraft, predicting the RCS of the simulated shock field, intuitively reflecting the physical scattering process, and applicable to the radar detection principle verification simulation test of the shock field of supersonic aircraft.

[0007] To achieve the above objectives, the present invention provides a method for simulating, predicting, and measuring the shock field of an aircraft. The method uses a horn antenna to simulate a typical aircraft shock field, predicts the radar cross section (RCS) of the simulated aircraft shock field, and uses the principle of radar coherent detection to measure the simulated aircraft shock field.

[0008] The simulation method includes:

[0009] Perform transient three-dimensional external flow field simulation modeling for an aircraft under supersonic cruise;

[0010] The three-dimensional external flow field is subjected to spectral analysis to obtain the dominant frequency, and the dielectric constant of the dominant frequency component is obtained by dielectric constant analysis of the three-dimensional external flow field.

[0011] Set the frequency range of the horn antenna with the main frequency of the aircraft shock field as the center frequency.

[0012] The power of the horn antenna is set to the sound pressure of the shock field of the aircraft as the transmission power;

[0013] Set the frequency range of the measuring radar, calculate the acoustic wavelength of the dominant frequency of the shock field, and set the center frequency of the measuring radar to satisfy the Bragg condition. The expression for the Bragg condition is:

[0014] λ=2nλ a

[0015] Where λ is the wavelength of the electromagnetic wave emitted by the measuring radar, λ a The wavelength of the sound wave emitted by the horn antenna is n = 1, 2, ..., taking natural numbers, and generally n = 1.

[0016] The estimation method includes:

[0017] The formula for calculating the RCS of the measurement area is:

[0018]

[0019] Among them, R a θ is the distance from the acoustic antenna to the center of the sound field packet. 3dB N is the 3dB beamwidth of the horn antenna, N is the number of sound field layers in the measured area, and P is... a G is the power at the sound field being measured. a This is the gain of the horn antenna, λ. a The wavelength of the sound wave emitted by the horn antenna;

[0020] Sound pressure level (SP) and power P a The relationship between them is:

[0021]

[0022] Where ρ is the air density, v a It refers to the speed of sound, and Area is the spherical surface area determined by the width of the sound wave beam. Sound pressure level is the logarithm of the ratio of sound pressure to reference sound pressure, SPL = 20log 10 (SP / P ref ), P ref =2×10 -5 Pa.

[0023] The measurement method includes:

[0024] When the audio signal generator is turned on, the broadband sound wave signal generated by the audio signal generator is radiated into the atmosphere by the horn antenna. At the same time, the measuring radar emits electromagnetic waves in the direction of relative sound wave propagation and intercepts the reflected electromagnetic waves of the sound field.

[0025] The audio signal generator is turned off, and the measuring radar emits electromagnetic waves in the direction of relative sound wave propagation and intercepts the reflected electromagnetic waves of the sound field;

[0026] The test data were compared and analyzed to obtain sound field scattering data.

[0027] The horn antenna and the measuring radar antenna are placed side by side on the ground, with both antennas oriented perpendicular to the ground. The center frequency and frequency scanning range of the horn antenna are set based on the dominant frequency obtained from the spectral analysis of the external flow field and the Bragg condition; the radiated sound pressure level of the horn antenna is set based on the sound pressure intensity of the aircraft shock field.

[0028] The experimental method for simulating shock fields and verifying coherent detection principles of aircraft provided by this invention uses a horn antenna to simulate the physical characteristics of shock fields and a high-power radar to detect them at the Bragg matching frequency, obtaining characteristic quantities such as power spectrum, RCS, and frequency shift. This method can intuitively reflect the physical scattering process and is easy to understand. It provides a principle verification method for detecting the external flow field of supersonic aircraft and is applicable to the electromagnetic scattering detection problem of atmospheric flow fields. Attached Figure Description

[0029] Figure 1 This is a flowchart of the present invention.

[0030] Figure 2 This is the experimental layout diagram of the present invention.

[0031] Figure 3 This is a schematic diagram of the shock field of a certain aircraft.

[0032] Figure 4 Yes Figure 3 The obtained characteristic spectrum was analyzed. Detailed Implementation

[0033] The following is based on Figures 1-4 The preferred embodiments of the present invention will be described in detail below.

[0034] As a mechanical wave, the shock wave from an aircraft compresses the air as it propagates through the atmosphere, creating a sound field with continuously varying density. When detecting the electromagnetic scattering characteristics of this atmospheric sound field as a scatterer, it can be considered as a medium with extremely low and continuously varying dielectric constant. This invention uses a horn antenna to simulate the shock wave field of an aircraft and designs a high-power radio frequency test system (including conventional radar components such as transmitters, receivers, antennas, and amplifiers) to simulate the radar coherent detection principle of the shock wave field for testing. The method proposed in this invention is applicable to the radar detection principle verification simulation test of supersonic aircraft shock waves and is suitable for electromagnetic scattering detection problems in atmospheric flow fields.

[0035] like Figure 1 As shown, this invention provides a method for simulating, predicting, and measuring the shock field of an aircraft. It uses a horn antenna to simulate a typical aircraft shock field and measures the simulated shock field using a high-power radio frequency test system based on the principle of radar coherent detection. The simulation method includes:

[0036] Step S1 Figure 3 The diagram shows a shock field of a certain aircraft. The transient three-dimensional external flow field simulation model of the aircraft under supersonic cruise is carried out. The transient flow field modeling and transient flow field characteristic calculation of the aircraft are studied. The pressure intensity and characteristic frequency of the transient flow field of a typical supersonic aircraft are obtained, which provides data support for the simulation and verification test of the electromagnetic scattering characteristics of the accompanying sound field of the aircraft.

[0037] Step S2 Figure 4 The figure shows the characteristic spectrum obtained from the analysis. The three-dimensional external flow field obtained in step 1 is subjected to spectrum analysis to obtain the main frequency. The three-dimensional external flow field obtained in step 1 is subjected to dielectric constant analysis to obtain the dielectric constant of the main frequency component.

[0038] Step S3: Set the frequency range of the horn antenna, with the main frequency of the aircraft shock field as the center frequency. In this example, the main frequency is 3kHz.

[0039] Step S4: Set the power of the horn antenna, using the sound pressure of the shock field of the aircraft as the transmission power. In this embodiment, the sound pressure is 125W, which corresponds to a sound pressure level of 119dB.

[0040] Step S5: Set the frequency range of the measuring radar system, test the weather conditions such as wind speed and temperature on the day, calculate the sound wave wavelength of the main frequency of the shock field, and set the center frequency of the measuring radar to meet the Bragg condition (the Bragg condition is that the wavelength of the electromagnetic wave is 2n times the wavelength of the sound wave, where n is an integer).

[0041] Set the frequency range of the measuring radar, calculate the acoustic wavelength of the dominant frequency of the shock field, and set the center frequency of the measuring radar to satisfy the Bragg condition. The expression for the Bragg condition is:

[0042] λ=2nλ a

[0043] Where λ is the wavelength of the electromagnetic wave emitted by the measuring radar, λ a The wavelength of the sound wave emitted by the horn antenna is n = 1, 2, ..., taking natural numbers, and generally n = 1. In the embodiment, the corresponding electromagnetic wave wavelength λ = 0.22m corresponds to a center frequency of 1.36GHz.

[0044] Step S6, the formula for calculating the RCS of the measurement area is:

[0045]

[0046] Among them, R a θ is the distance from the acoustic antenna to the center of the sound field packet. 3dB N is the 3dB beamwidth of the horn antenna, N is the number of sound field layers in the measured area, and P is... a G is the power at the sound field being measured. a This is the gain of the horn antenna, λ. a The wavelength of the sound wave emitted by the horn antenna;

[0047] Sound pressure level (SP) and power P a The relationship between them is:

[0048]

[0049] Where ρ is the air density, v a It refers to the speed of sound. Area is the spherical surface area determined by the width of the sound wave beam. (See reference...) Figure 2 Experimental layout diagram, Sound pressure level is the logarithm of the ratio of sound pressure to reference sound pressure, SPL = 20log 10 (SP / P ref ), P ref =2×10 -5 Pa;

[0050] In this embodiment, R a With a depth of 100m, a sound wave layer number N of 200, and a beamwidth of 10° for the horn antenna, the RCS of the sound field obtained using the above estimation formula is -29dBm. 2 ;

[0051] The measurement method includes:

[0052] Step S7: A broadband sound wave is generated by an audio signal generator, and the sound is radiated into the atmosphere by a directional horn antenna. At the same time, the radar emits electromagnetic waves in the direction relative to the sound wave propagation and measures the reflected electromagnetic waves intercepted by the radar from the sound field. The audio signal generator is tested in two states, when it is off and when it is on, and the results are compared and analyzed.

[0053] Step S8: Analyze the test data.

[0054] In one embodiment of the present invention, such as Figure 2 As shown, the experimental setup involves placing the horn antenna and the measuring radar antenna side-by-side on the ground. Both the horn antenna and the measuring radar antenna are oriented perpendicular to the ground, meaning they emit sound and electromagnetic waves directly into the sky. Figure 2 The angular separation of the mid-sound horn antenna and the measuring radar antenna indicates their illumination range. This invention proposes a radar coherent detection principle verification test method for the shock field generated during supersonic cruise of an aircraft. The specific steps are as follows:

[0055] Step 1: Conduct transient three-dimensional external flow field simulation modeling for the supersonic cruise of the aircraft, carry out transient flow field modeling and transient flow field characteristic calculation research for the aircraft, obtain the pressure distribution of the transient flow field of a typical supersonic aircraft, and provide data support for the simulation verification test of the electromagnetic scattering characteristics of the accompanying sound field of the aircraft.

[0056] Step 2: Perform spectrum analysis on the three-dimensional external flow field obtained in Step 1 to obtain the main frequency. In the preferred embodiment, the frequency is 3kHz and the sound pressure level is 120dB.

[0057] Step 3: Set the center of the horn antenna to 3kHz and the frequency scanning range to 2.5kHz~3.5kHz;

[0058] Step 4: Set the radiated sound pressure level of the horn antenna to 120dB;

[0059] Step 5: Set the frequency of the measuring radar to 1.3 GHz;

[0060] Step 6: Assemble the horn antenna and measuring radar system as follows. Figure 2 The experimental setup shown is as follows: an audio signal generator produces broadband sound waves, which are radiated into the calm atmosphere by a directional horn antenna. Simultaneously, a radar emits electromagnetic waves relative to the direction of sound wave propagation and measures the reflected electromagnetic waves intercepted by the radar from the sound field. The test involves two states: the audio signal generator is off and on. The specific test steps are as follows:

[0061] Step 6.1: Install and debug the electromagnetic testing system, focusing on testing the performance of the microwave high-speed switch and whether it has the ability to capture targets within 60m of the background at a depth of -30dBsm.

[0062] Step 6.2: Install and test the horn antenna;

[0063] Step 6.3: A broadband acoustic signal is emitted by an audio signal generator, and electromagnetic waves are emitted by a measuring radar to detect and receive the signal.

[0064] Step 6.4: Turn off the audio signal generator source and perform the same comparison test;

[0065] Step 6.5, Calibration Test;

[0066] Step 7: Perform calibration and background removal on the test data to obtain sound field scattering data.

[0067] Step 8: Analyze the test data.

[0068] As can be seen from the preferred embodiments, the aircraft shock field simulation and coherent detection principle verification test method provided by the present invention uses a horn antenna to simulate the physical characteristics of the shock field and uses a high-power radar to detect at the Bragg matching frequency to obtain characteristic quantities such as power spectrum, RCS, and frequency shift. It can intuitively reflect the physical scattering process and is easy to understand, providing a principle verification method for the detection of the external flow field of supersonic aircraft.

[0069] It should be noted that, in the embodiments of the present invention, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0070] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for simulating, predicting, and measuring the shock field of an aircraft, characterized in that, A typical aircraft shock field is simulated using a horn antenna. The radar cross section (RCS) of the simulated aircraft shock field is estimated, and the simulated aircraft shock field is measured using the principle of radar coherent detection. The method for simulating a typical aircraft shock field includes: Perform transient three-dimensional external flow field simulation modeling for an aircraft under supersonic cruise; The three-dimensional external flow field is subjected to spectral analysis to obtain the dominant frequency, and the dielectric constant of the dominant frequency component is obtained by dielectric constant analysis of the three-dimensional external flow field. Set the frequency range of the horn antenna with the main frequency of the aircraft shock field as the center frequency. The power of the horn antenna is set to the sound pressure of the shock field of the aircraft as the transmission power; Set the frequency range of the measuring radar, calculate the acoustic wavelength of the dominant frequency of the shock field, and set the center frequency of the measuring radar to satisfy the Bragg condition. The expression for the Bragg condition is: in To measure the wavelength of electromagnetic waves emitted by radar, The wavelength of the sound wave emitted by the horn antenna. Take a natural number.

2. The method for simulating, predicting, and measuring the shock field of an aircraft as described in claim 1, characterized in that, The method for estimating the radar cross section (RCS) of the simulated aircraft shock field includes: The formula for calculating the RCS of the measurement area is: in, It is the distance from the acoustic antenna to the center of the sound field packet. It is the 3dB beamwidth of the horn antenna. N It is the number of sound field layers in the measured area. It is the power at the sound field being measured. It is the gain of the horn antenna. The wavelength of the sound wave emitted by the horn antenna; Sound pressure level (SP) and power The relationship between them is: in, It is air density. It refers to the speed of sound, and Area is the spherical surface area determined by the width of the sound wave beam. The sound pressure level is the logarithm of the ratio of the sound pressure level to the reference sound pressure level. , Pa.

3. The method for simulating, predicting, and measuring the shock field of an aircraft as described in claim 2, characterized in that, The method for measuring the simulated shock field of an aircraft includes: When the audio signal generator is turned on, the broadband sound wave signal generated by the audio signal generator is radiated into the atmosphere by the horn antenna. At the same time, the measuring radar emits electromagnetic waves in the direction of relative sound wave propagation and intercepts the reflected electromagnetic waves of the sound field. The audio signal generator is turned off, and the measuring radar emits electromagnetic waves in the direction of relative sound wave propagation and intercepts the reflected electromagnetic waves of the sound field; The test data were compared and analyzed to obtain sound field scattering data.

4. The method for simulating, predicting, and measuring the shock field of an aircraft as described in claim 3, characterized in that, The horn antenna and the measuring radar antenna are placed side by side on the ground, with both the horn antenna and the measuring radar antenna facing perpendicular to the ground.

5. The method for simulating, predicting, and measuring the shock field of an aircraft as described in claim 4, characterized in that, The center frequency and frequency scanning range of the horn antenna are set according to the main frequency obtained from the spectral analysis of the external flow field and the Bragg condition; the radiated sound pressure level of the horn antenna is set according to the sound pressure intensity of the shock field of the aircraft.

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