In the process of target re-entry, since the target enters the atmosphere at a high speed, the violent friction between the target and the atmosphere generates aerodynamic heat, which makes the target surface heat up rapidly and generates a strong radiation signal. It is an important factor in the target detection process. In order to calculate the surface temperature caused by the aerothermal effect quickly, a rapid prediction model of temperature characteristics is proposed in this paper. Based on the temperature of stagnation point and the surface temperature distribution obtained by the summary analysis with accurate simulation calculation, The surface temperature distribution characteristics during the target re-entry process can be estimated quickly.
In order to study the variation law of radiation characteristics of high temperature gas with altitude in medium and low altitude environment, the spectral radiation characteristics of three mixed gases containing H2O, CO2 and CO at different temperatures and pressures were calculated by LBL (Line by line) method, so as to analyze the corresponding changes of spectral radiation intensity of high temperature gas with the change of overall temperature and pressure, and explain the reason why the radiation spectrum changes with altitude. The results showed that the influence of temperature on the radiation intensity was more significant than that of pressure; at the same time, with the decrease of temperature, the peak value of spectral radiation gradually moved to the middle wave band, and the radiation intensity at 4.3 μm, which is the radiation band of CO2, and 4.7 μm, which is the radiation band of CO, gradually increased. However, due to the greater sensitivity of CO to the change of pressure, the relative radiation intensity at 4.7 μm after the pressure was reduced.
Photon is an ideal carrier of quantum information, which can carry spin angular momentum and orbital angular momentum. In recent years, orbital angular momentum has shown great application prospects in quantum communication, quantum radar and other fields. It has gradually become a research hotspot in the field of detection. It is necessary to calibrate and measure the orbital angular momentum before it is applied to the detection field. Based on the interference principle and aperture diffraction theory, the measurement of orbital angular momentum is realized indirectly, and the experimental platform is built to verify part of the simulation results. It provides technical support for the subsequent implementation of quantum detection technology.
In order to study the transmission characteristics of orbital angular momentum in the atmosphere, MATLAB software is used to simulate it. The power spectrum inversion method and subharmonic compensation theory are used to construct a random phase screen to simulate the atmospheric turbulence effect. The effects of different topological charges, turbulence intensity and transmission distance on the orbital angular momentum intensity, phase and spiral spectrum distribution are studied. It provides support for the new quantum detection technology.
In order to study the infrared target characteristics of "low slow small" aircraft, the infrared target characteristics of six rotors unmanned aerial vehicle (UAV) are studied by numerical calculation. Considering the aerodynamic heating effect of rotor, and the radiation effect of the sun and the earth's atmosphere on the target, the changes of the target's radiation intensity in the three infrared bands of 1 ~ 3 μ m, 3 ~ 5 μ m, 8 ~ 12 μ m at night and in the daytime are studied under different observation angles. The results show that in the medium / long wave band, the target's infrared radiation mainly comes from the reflection of its own radiation and the earth's atmosphere, so its radiation characteristics change little in the daytime and at night, while for the short wave, the target's radiation intensity in the daytime is greater than that in the evening; the target's radiation intensity is directly related to the observation area, and the radiation intensity is the smallest in the positive and lateral observation, while the radiation intensity in the upward and The radiation intensity is the highest when looking down.
Aiming at the problem that infrared detectors can only measure the surface radiation of a target while flying in space. And it is difficult to obtain the hollow scale of the target. This paper designs a method for inverting the hollow scale based on the dynamic change of radiation energy. Taking a hollow sphere as an example, the relationship between the target radiation intensity and the hollow scale and time is given. Analyzed the relationship between the target radiation amount its influencing factors. On this basis, the ralationship feature between radiation and hollow scale under different time conditions is given. Through the method in this paper, hollow scale of the target can be estimated to support target detection and recognition analysis.
The measurement of radiant heat flux in flame tube is usually non-contact, so various factors should be considered in the actual measurement process. In order to improve the accuracy of measuring radiant heat flux on the inner wall of the flame tube, a flame tube model was used as the research object in this paper. A high temperature gas radiant heat flux wind tunnel measurement system was established to measure the wall radiant heat flux under different combustion conditions. The results of the test and numerical simulation were compared, and the relative error between the revised test and numerical simulation results was kept between -38.89% and 32.54%.
Exhaust plume from the rocket engine produces strong infrared radiation signals, widely used for target diagnosing, detecting and identifying. Exhaust plume flow field have the characteristics of high temperature, high speed and multi-species reacting flow. The radiation mechanism is very complex in the flow field. Infrared spectrum of exhaust plume involving complex gaseous kinetic and thermodynamic processes, which makes the exhaust plume have a complex spectral structure. On the base of a rocket motor, the two-dimensional axisymmetric and Reynolds Averaged Navier-Stokes equations (RANS) coupled with chemical reactions are solved. With the flow field of the exhaust plume, line-by-line method and LOS method are used to calculate the infrared radiation of the exhaust plume. The spectral radiation characteristics of H2O, CO2, CO and HCL in 2μm to 8.6μm band are analyzed in detail, and the characteristics of radiance distribution in typical gas emission bands are studied.
In order to study the infrared radiation characteristics of the solid rocket plume at high altitude, a numerical method is used to simulate the infrared spectral radiation intensity of a solid rocket plume at three altitudes, which are 120km, 150km and 180km, and the cause of the phenomenon is produced from the flow and radiation transmission views. It is confirmed that the peak value of infrared radiation intensity of the plume is within the range of 4~5 μm, due to the influence of high altitude diffusion effect. At the high altitude, the infrared radiation intensity of the plume increases rapidly at 4.7μm, which is at the CO absorption band. It can be within the same magnitude as the radiation intensity at the 4.3μm, which is at the CO2 absorption band. And the radiation intensity varies slowly with height, there is no severe fluctuation.
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