# Correction of Aero-Optical Effect with Blow-Suction Control for Hypersonic Vehicles
## 4 Results and Discussion
### Aero-Optical Effect Correction with Jet Flow
Nevertheless, upon introducing jet flow (Case2 condition), significant density fluctuations are observed upstream of the flow mixing zone due to the disturbance caused by jet flow interaction. Figure 16b compares how reduced jet flow impacts density pulsation. It can be observed that when comparing Case5 (jet flow = 0.05 kg/s) with Case8 (jet flow = 0.01 kg/s) under similar jet modes, reduced jet flow significantly diminishes density pulsation while also weakening aero-optical transmission effects accordingly. Furthermore, compared to Case8 (\(\theta=15^{\circ}\)) and Case9 (\(\theta=15^{\circ}\)), decreased gas injection leads to a reduction in \(\rho_{\rm rms}\), influenced by different jet modes. It can be seen from Figure 17 that the RMS of optical window density varies greatly along the longitudinal direction, mainly in the vicinity of the near-wall turbulent boundary layer and shock wave in the flow field. The parameters of the flow field in the turbulent boundary layer near the wall of the (high) supersonic flow field have a large gradient due to the influence of  
Figure 16: \(\rho_{\rm rms}\) distribution in spanwise direction under different flow field conditions: (**a**) Case0 to Case6; (**b**) Case4 to Case9. Figure 15: \(\rho_{\rm rms}\) distribution in flow direction under different flow field conditions: (**a**) Case0 to Case6; (**b**) Case4 to Case9. turbulence, so there will be a large deflection phenomenon when the ray passes through the flow field of the turbulent boundary layer. Since the density field of the (hypersonic) supersonic flow field has a great gradient when passing through the shock wave, the refractive index field determined by the density field will naturally have a large gradient near the shock wave, so the ray will also have a large deflection when passing through the shock wave. The comparison of Case1 (without jet) and Case3 (jet flow = 0.05 kg/s) in Figure 17a shows that, due to the difference between the two conditions, only with or without jet flow, it can be seen that when the jet flow is tangent parallel to the window, a great gradient value appears near the window wall, and the root mean square of density rises sharply, reaching a maximum value of \(\rho_{\rm rms(max)}=0.7\) kg/m\({}^{3}\). It can be concluded that the light will have a large deflection here. However, after \(z/\delta=5\), the \(\rho_{\rm rms}\) values under the two conditions tend to be consistent due to the weakening of the near-wall flow field interference. Case4 (jet flow = 0.05 kg/s, \(\theta=90^{\circ}\)) is the case of jet flow perpendicular to the axis, and the root mean square of density near the wall also has an extreme value of \(\rho_{\rm rms}\approx 0.27\), but because it is upstream of the window, it is close to the shock wave. In Figure 17a, the dimensionless distance along the longitudinal direction is denoted as \(z/\delta\). Here, \(z/\delta=0\) corresponds to the window surface, while \(z/\delta\approx 7\) is in close proximity to the shock layer of the seeker's outflow field. It can be observed that \(\rho_{\rm rms}\) exhibits an extreme state under all working conditions at this location. Due to the perpendicular orientation of Case4 jet with respect to the seeker axis, the emitted cooling gas encounters and interacts with the shock layer of the seeker's flow field, resulting in the formation of an interference structure. Consequently, the \(\rho_{\rm rms}\) near the shock wave tends to be slightly larger compared to its state without jet.