# Correction of Aero-Optical Effect with Blow-Suction Control for Hypersonic Vehicles
## 1 Introduction  
When a missile flies at high speed in the atmosphere, the optical guidance hood of the missile interacts strongly with the surrounding gas, resulting in the formation of turbulent boundary layers, shock waves, and expansion waves around the optical hood. These complex flow structures create density gradients in the flow field outside the missile hood. When the missile-borne imaging system captures and identifies targets while tracking them, light waves passing through this non-uniform refractive index gradient in the flow field cause optical distortion, leading to the migration, blurring, jittering, and energy attenuation of the target images. This phenomenon is known as aero-optical effect [1, 2]. However, during high-speed flight, aero-thermal factors cause a rapid rise in temperature on the outer surface of the optical window of an optical seeker. This leads to a gradient distribution and may cause shape change or even structural damage of the optical window [3]. Therefore, it is crucial to develop effective cooling measures for hypersonic vehicles' optical windows to reduce aerodynamic thermal radiation effects and improve optical imaging. In recent years, there has been increasing attention to aero-optical effects due to the development of airborne laser communication platforms, high-speed missiles with optical seekers, and laser weapon systems. The correction of aero-optical effects mainly focuses on flow control and image processing. Many scholars have made significant advancements in the correction of aero-optical effects within the mixing layer [4, 5]. [PERSON] et al. [6, 7] proposed a backward ray-tracing method for the aero-optics simulation of a typical blunt-nosed vehicle,which has improved the convenience of calculation. [PERSON] et al. [8; 9; 10] conducted an extensive investigation into the temporal and spatial development of the supersonic mixing layer and proposed a correction strategy through flow control by periodic pulse forcing. In 1966, [PERSON] [11; 12; 13] provided a definitive elucidation of jet cooling, while also investigating the empirical formulation for gas film cooling efficiency and the impact of slit shape on gas film cooling. [PERSON] and [PERSON] [14] used a two-dimensional Shack-Hartmann wavefront sensor to study aero-optical distortion in turbulent boundary layers at transonic and hypersonic speeds, with and without gas injection. [PERSON] et al. [15] analyzed the characteristics of optical beams propagating through a shock wave resulting from supersonic motion of a conical body in a turbulent atmosphere. It was shown that the aero-optical effects caused by a shock wave are suppressed with an increase in optical turbulence. [PERSON] et al. [16] used the ray tracing method to study the effects of different altitudes, attack angles, beam incidence angles, and Mach numbers on beam propagation in the study of aero-optics effects caused by the flow field around hypersonic vehicles in near-space. It was found that the aero-optical effects become more serious in the presence of jet compared to the absence of jet. Later, [PERSON] et al. [17] investigated the influence of altitude on aero-optic imaging quality degradation of the hemispherical optical dome. The results showed that under the same flight conditions, with the increase in altitude, the peak signal-to-noise ratio (PSNR) of the distorted image and the SR result increased, and the radiuses of dispersion spots, including 80% energy, decreased. [PERSON] et al. [18; 19] investigated the aero-optics of the external jet cooling and shock wave in a shock-wave wind tunnel. Moreover, [PERSON] [20] employed the DSMC method to investigate the impact of different jet modes on aero-optics-induced image migration, and the results demonstrated that the horizontal jet mode yields superior results in terms of window cooling. Experimental research conducted by [PERSON] et al. [21] revealed that the utilization of micro-vortex generators has significantly contributed to enhancing wavefront stability.