Objective  Divert and attitude control system's side jet flow is ejected along the normal direction of the projectile during operation, which will form a series of complex structural flow fields called jet interference effects. The high-temperature jet not only generates infrared radiation but also affects the temperature distribution on the surface of the projectile, which ultimately affects the radiation characteristics of the target. In particular, the DACS operation is often accompanied by a change in the angle of attack. The change in the angle of attack causes a significant change in the jet interference effect, which can cause significant changes in the infrared radiation characteristics of the target. In the field of attack-defense mutual countermeasures, both for the stealth and surprise defense of interceptors and for the evasion and identification of interceptors, the urgent concern for the infrared radiation characteristics of targets under high-speed jets is raised. The paper analyzes the effects of the angle of attack on the reignition of the thermal jet field at typical altitudes, and the effects of the angle of attack on the infrared radiation characteristics of the projectile in different spectral bands and at different observation angles.

  Methods  With the typical cone-cylinder-flare elastomer as the research object (Fig.1), the three-dimensional N-S equation with chemical reaction source terms is solved. The reaction thermal jet field and the wall temperature of the projectile are calculated in conjunction with the radiative equilibrium wall. The radiative transfer equations are solved based on the statistical narrow band model and the apparent light method from the high temperature database. A Cartesian coordinate system is used to describe the radiation distribution at all possible angles, and the observed angles are represented by the zenith angle θ and the circumferential angle φ (Fig.3).

  Results and Discussions   Compared to α=0°, the Mach disk increases at α=10°, the jet expands upward and the high-temperature area increases. However, the Mach disk decreases at α=−10°, the jet is compressed into a limited area of elongated shape, and the local wall temperature at the tail of the projectile increases by about 500 K (Fig.5). The reignition effect increases the intensity of infrared radiation in the MWIR band of the target by about 3.5%, and the degree of radiation intensity increase at α=−10° is enhanced by about 145% compared with α=0° and reduced by about 31.5% at α=10° (Fig.8). The peak radiation intensity of the near-space aircraft proper spectrum is concentrated in the MWIR band, and is strongest in the top view and weakest in the back view, 1 836.6 W/sr and 7.6 W/sr at α=0°, respectively; The total radiation spectrum has two peaks of 2.7 μm (H₂O) and 4.3 μm (CO₂). The integrated intensity of radiation in the two bands of the same detection surface shows a similar distribution pattern with the change of observation angle and angle of attack, but the difference of radiation intensity values is obvious, which is approximately in line with the pattern that the integrated intensity in the MWIR band is 4 times higher than that in the LWIR band. 4 times the law. In the detection surface 1 described by the zenith angle θ, when α =−10°, the total radiation integral intensity in the top view is enhanced by about 40.2% compared with α = 0°, and reduced by about 28.1% in the top view; When α = 10°, the total radiation integral intensity in the top view is reduced by about 8.6% compared with α = 0°, and enhanced by about 27.8% in the top view; In the detection surface 2 described by the circumferential angle φ, when α =−10°/10°, the total radiation integral intensity is reduced by about 7.5%, and when α =−5°/5°, the total radiation integral intensity is reduced by about 4.8% (Fig.9-14).

  Conclusions  When the side jet stream acts, a local hot spot is formed on the wall surface of the projectile. Changes in the angle of attack cause changes in the jet pattern, the temperature distribution at the wall, and the concentration distribution of the gas components, which change the re-ignition level and the radiation intensity. The radiation intensity of the projectile is strongly dependent on the waveband and the observation angle. The total radiation intensity is mainly derived from body radiation. The change of the angle of attack affects the radiation intensity of the target at each observation angle as follows. The radiation intensity of the target in the top view decreases with the negative to the positive angle of attack, and the radiation intensity of the target in the horizontal plane normal to the jet decreases with the increasing value of the angle of attack. This study can provide a theoretical reference for the identification of the target characteristics of the near-space aircraft side jet flow.