Objective   Driven by military applications, the new generation of precision-guided weapons continues to develop toward improved guidance and strike accuracy. Imaging deviation is an important indicator of the aero-optics effect, which portrays the deflection effect of the aero-optics flow field on light propagation. The study of the imaging deviation of aero-optics can improve the guidance and strike accuracy of aircraft and provide support for the development of high-end military equipment in China, so it is necessary to conduct an in-depth study of its related problems.

  Methods   A typical blunt-headed vehicle was modeled and meshed using software (Fig.2) and a large number of flow field calculations were made based on the computational fluid dynamics software Fluent to obtain the flow field density around the vehicle under different operating conditions (Fig.5). The corresponding refractive index distribution was obtained by the correspondence between density and refractive index. The light transmission equation was solved using the fourth-order Runge-Kutta method, and the imaging deviation data were obtained using the inverse ray tracing method and the stopping criterion.

  Results and Discussions   The analysis of the refractive index distribution at different altitudes in the reverse light tracing (Fig.6) shows that the refractive index increases and then decreases along the propagation path as the light enters the aerodynamic optical flow field. The light tracing starts from the starting point inside the window, and the refractive index increases and then decreases against the direction of light incidence through the non-uniform flow field and finally reaches the free flow refractive index decreases until the end of the tracing. The refractive index of the non-uniform flow field near the optical window decreases with increasing altitude, and although the refractive index distribution of the light propagation path at different altitudes has the same trend, it has a different degree of change. As the altitude increases, the refractive index distribution on the light propagation path becomes flatter and the imaging shift becomes smaller (Fig.7, Fig.9, and Fig.11). Within 0-25 km, the slope of the imaging deviation increases in the negative direction of 0 as the angle of attack increases, indicating that a larger change in angle of attack results in a larger imaging deviation. The slope of 0° angle of attack is closer to 0 for the same altitude condition, which indicates that 0° angle of attack is the least sensitive to changes in deviation values. Also as the altitude increases, the slope of the deviation at the same angle of attack gradually approaches 0 in the negative direction of 0, which also indicates that a change in lower altitude causes a larger imaging deviation (Fig.8, Fig.10, and Fig.12).

  Conclusions  The effect of different altitudes of 0°-15° angle of attack on the aero-optical imaging deviation of the blunt-headed vehicle was investigated. The computational analysis of the imaging deviation for every 1° angle of attack in the 0°-15° range was carried out one by one. The results of the study show that as the altitude increases, the refractive index distribution of the light propagation path at different altitudes becomes flatter and the imaging deviation value becomes smaller. As the angle of attack increases, the refractive index distribution on the light propagation path becomes more uneven, and thus the imaging deviation increases. The slope of the imaging deviation approaches 0 at higher altitudes and increases in the negative direction of 0 at larger angles of attack. This indicates that the imaging deviation value will show a large variation at low altitudes and a large angle of attack. The results show that the effect of a high Mach number at 25 km on the imaging deviation is greater than that of atmospheric density, and this result is going to be analyzed in the future in a comprehensive analysis of the results of high Mach number calculations for more different operating conditions, and then to explore the influence of related factors on practical applications. The results are expected to give a reference for theoretical calculations for the integrated design of flight altitude, velocity, and imaging attitude of infrared-guided vehicles.