# Correction of Aero-Optical Effect with Blow-Suction Control for Hypersonic Vehicles
## 4 Results and Discussion
### Aero-Optical Effect Correction with Jet Flow
Subsequently, the impact of different jet angles and flow rates on the reduction of window temperature is compared under decreased inlet pressure conditions, as depicted in Figure 14 below. Figure 14a illustrates the temperature distribution across the window when a jet flow rate of 0.05 kg/s is employed at Mach 5 flight speed and an altitude of 30 km. The figure clearly demonstrates a significant cooling effect on the window, with minimal temperature fluctuations, which can be attributed to reduced total pressure resulting in diminished external interference from cooling gas and facilitating efficient heat absorption near the window surface. In Figure 14b, where a perpendicular jet mode is utilized, it becomes evident that temperatures near the rear step are higher, due to vertical jets disrupting the normal free flow and causing increased separation zones, along with larger return regions at the back step, consequently leading to elevated temperatures. Excessive cooling gas carried downstream by free flow enhances cooling effectiveness for downstream windows compared to upstream positions. The temperature distribution of the window gradually increases in Figure 14c,d as the jet flows decrease, while still maintaining directionality towards flow progression. In summary, both jet modes improve the wall temperatures of windows compared to back-step flow fields without jets. Among them, tangentially parallel window jet cooling exhibits superior performance over vertical axis jet cooling. The objective of this section is to investigate the correction method for mitigating the aero-optical effect, which arises from the combined influence of temperature variations in the optical window wall and flow field development. Essentially, the aero-optical-induced optical transport effect is caused by density fluctuations in the flow field. In theory, suppressing density fluctuations in the flow field can effectively suppress the aero-optical effect. Figure 15 presents density pulsation information along the symmetric surface of the optical hood for different flow conditions. Based on our analysis, jet cooling proves effective in reducing aerodynamic heat radiation through windows. However, as shown in Figure 15a, under the Case0 and the Case1(without jet) conditions, there is minimal density pulsation, along with negligible additional disturbance effects. Conversely, after introducing jet flow (Case2 and Case3), due to disturbances induced by jet flow, density pulsations increase noticeably upstream within the flow mixing zone but rapidly decrease downstream, along with fluid motion directionality. Comparing Case4 (\(P=5529\)and Case6 (\(P=1197\)) reveals that increasing flight altitude significantly reduces density fluctuation at identical Mach numbers. Figure 15b compares how decreasing jet flow affects density pulsation levels; it becomes evident that only reducing jet flow leads to significant reductions in density pulsation under similar jet patterns--thus indicating an expected weakening of aero-optical transmission effects as well. Further comparison between Case8 (\(\theta=15^{\circ}\)) and Case9 (\(\theta=90^{\circ}\)) demonstrates that changes in jet angle also result in reduced impact on fluid field densities owing to the cooling gas reduction. The density pulsation information in the flow field is directly associated with the aero-optical effect problem. Figure 16 illustrates the RMS density distribution in the lateral direction of the optical window at \(y/\delta=6.25\). Based on the aforementioned analysis, jet cooling proves effective in mitigating the aerodynamic heat radiation phenomena on the window surface. However, as depicted in Figure 16a, under the Case0 and Case1 (without jet) conditions, there is relatively uniform \(\rho_{\rm rms}\) distribution in the lateral direction, with minimal influence from additional disturbances.