# Correction of Aero-Optical Effect with Blow-Suction Control for Hypersonic Vehicles
## 4 Results and Discussion
### Aero-Optical Effect Correction with Jet Flow  
This section focuses on investigating the impact of different jet modes on the aerodynamic heating effect of the seeker's optical window and analyzing the disparities in aero-optical effects caused by two nozzle modes with varying orientations. The thermal radiation of the infrared window is a crucial factor that limits infrared imaging. Therefore, the primary issue addressed by the cooling jet is the degradation of imaging quality caused by aerodynamic heat, resulting in a decrease in window temperature. Figure 13 illustrates the distribution of window temperature under four different operating conditions. Figure 13a represents the temperature distribution without jet cooling. As velocity increases, the flow field experiences stronger compression, leading to higher peak pressure and density on the optical window. Simultaneously, the shock layer at the front end of the hood becomes thinner, with a smaller shock angle. Due to this compression effect, as well as an increased flow-field temperature and heat flux on the optical window, the friction between the air medium and the wall intensifies, while imposing higher material requirements for optical windows with elevated wall temperatures. Consequently, higher speeds necessitate greater reliance on jet cooling to mitigate aerodynamic effects and safeguard optical windows from damage. It can be observed that at 5 Ma, aerodynamic heating causes an increase in window temperature up to 900 K. When the airflow encounters a step in its direction of flow, its velocity decreases, causing the conversion of kinetic energy into internal energy and a subsequent rise in temperature occurs. Upon leaving the optical window surface, encountering a compression corner further reduces the airflow speed while generating additional heat energy. Henceforth, this results in a high-low-high trend within the surface temperature distribution; however, these variations are minimal, with an approximate difference of only 30 K.  
The temperature distribution of the window during jet cooling parallel to the window at a speed of 5 Ma is illustrated in Figure 13b. It is evident that an effective reduction in window temperature can be achieved when the jet flow rate is 0.05 kg/s, resulting in an average temperature decrease to 150 K. However, as the cooling gas gradually dissipates along the direction of flow due to its parallel nature with respect to the window, the cooling effect diminishes and consequently leads to a gradual increase in window temperature. In Figure 13c, we observe the window temperature distribution when employing a perpendicular jet relative to the seeker axis under identical flight Mach number conditions. It becomes apparent that direct exposure of the cooling gas on the window surface is absent compared to the Case3 (\(\theta\) = 15\({}^{\circ}\)) mode, resulting in a weaker reduction in window temperature. This discrepancy primarily arises from significant changes in incoming flow velocity, caused by expansion waves formed upon encountering vertical jets, leading to  
Figure 13: Comparison of optical window temperature distribution under 5 Ma, \(P\) = 5529 Pa conditions: (**a**) without jet; (**b**) jet flow = 0.05 kg/s, \(\theta\) = 15\({}^{\circ}\); (**c**) jet flow = 0.05 kg/s, \(\theta\) = 90\({}^{\circ}\); (**d**) jet flow = 0.01 kg/s, \(\theta\) = 15\({}^{\circ}\). substantial reflux near the nozzle and dissipation of gas kinetic energy. Consequently, this results in inferior temperature drop effects compared to those observed with parallel jets. Figure 13d primarily investigates whether reducing jet flow has a notable impact on window cooling performance. As depicted in this figure, even when utilizing a reduced jet flow rate of 0.01 kg/s, there remains some degree of reduction in window temperature; however, due to limited amounts of cooling gas available at such low rates, rapid consumption occurs, along with diminishing effectiveness along the direction of flow.