# Correction of Aero-Optical Effect with Blow-Suction Control for Hypersonic Vehicles
## 4 Results and Discussion
### Aero-Optical Effect Correction with Micro Vortex Generators (MVGs)  
The temperature distribution of the optical window under \(Ma=3\) without jet cooling is compared in Figure 18 below. It can be observed that the temperature at the upstream position of the optical window is slightly higher with MVGs than without MVGs. Overall, there is little difference in the surface temperature between the two windows, which also indicates that MVGs will not play a role in cooling the windows without jet cooling measures. Figure 17: \(\rho_{\rm rms}\) distribution in longitudinal direction under different flow field conditions: (**a**) \(y/\delta=6.25\); (**b**) \(y/\delta=18.75\). Figure 18: Comparison of optical window temperature distribution under \(Ma=3\) without jet cooling: (**a**) without MVGs, (**b**) with MVGs. In order to directly compare the flow field with and without MVGs, Figure 19 illustrates the refractive index distribution near the optical window at \(Ma=3\) without jet cooling. Similarly, Figure 20 depicts the refractive index distribution near the optical window at \(Ma=5\) without jet flow. During high-speed flight, the flow field near the seeker undergoes compression into layers, resulting in air flow adherence to the seeker wall and the formation of a shock layer. The flow in the shock layer exhibits a narrow front and wide rear distribution. Considering the overall shape depicted in Figure 1a and the installation position shown in Figure 3 for MVGs, it can be concluded that their presence does not affect the bow shock wave present on the outer layer of the seeker. Additionally, due to turbulent boundary layer effects and associated low density, there is also a decrease in the refractive index near walls. However, regardless of whether \(Ma=3\) or \(Ma=5\), both cases exhibit similar distribution patterns for refractive indices without significant gradients. The temperature distribution in the optical window with jet cooling (\(Ma=3\), flow jet = 0.05 kg/s) is compared in Figure 21, where (a) is without MVGs and (b) is with MVGs. Due to the concave structure of the optical window, resistance is encountered when high-speed air flows through the vortex generator, resulting in a reduction in air velocity and transfer of heat from \"extra\" kinetic energy into the turbulent boundary layer, leading to a diminished cooling effect. The average surface temperature of the window with MVGs is approximately 30 K higher compared to that without MVGs, yet it generally satisfies the requirement for window cooling. However, the addition of MVGs results in a gradual increase in the window temperature distribution along the flow direction (\(\gamma\)-axis). Figure 19: Comparison of refractive index distribution near the optical window at \(Ma=3\) without jet cooling. Figure 20: Comparison of refractive index distribution near the optical window at \(Ma=5\) without jet cooling. The introduction of the cooling jet leads to a highly non-uniform refractive index distribution within the investigate area, primarily characterized by slight variations along the flow direction parallel to the wall (\(y\)-axis). Along the direction perpendicular to the window surface (\(z\)-axis), there is an initial increase, followed by a decrease in refractive index distribution, as illustrated in Figure 22. The addition of jet gas significantly enhances the complexity of flow field structure, resulting in distinct shear layer, mixing layer, and turbulent boundary layer structures near the window. Furthermore, both density and density gradient experience substantial increments within the flow field. A comparison between Figure 22a,b reveals that after incorporating micro-vortex generators, the pulsations in proximity to the window are considerably reduced, as indicated by the red dashed circle in the figure below. The comparison of temperature distribution in the optical window at \(Ma=5\) for jet cooling is illustrated in Figure 23 below.