# 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)
It can be observed that the addition of MVGs leads to a more uniform temperature distribution across the entire window, reducing the temperature difference between the highest and lowest points to only 4.5 K. In contrast, without MVGs, temperatures gradually increase along the flow direction, resulting in a significant difference of 42.8 K. This non-uniform temperature distribution induces stress-induced deformation in the window material, exacerbating both the elastic and aero-optical effects. Thus, it can be concluded that micro-vortex generators effectively enhance temperature uniformity within cooled jets. The turbulent boundary layer plays a crucial role in generating the aero-optics effect. In flow fields with higher Mach numbers, the stratification of the flow field becomes more pronounced due to increased compressibility. As shown in Figure 24, the addition of MVGs can still inhibit the formation of large-scale vortex structures. Figure 23: Comparison of optical window temperature distribution under \(Ma=5\) with jet cooling: (**a**) without MVGs, (**b**) with MVGs. Figure 22: Comparison of refractive index distribution near the optical window at \(Ma=3\) with jet cooling. The comparison of wavefront aberration with and without MVGs is depicted in Figure 25 below. It can be observed from Case10 (\(Ma=3\), without jet, with MVGs) that MVGs do not modify the amplitude of wavefront distortion. This can be attributed to the fact that the overall density gradient in the shock layer remains unchanged during downstream airflow development, transitioning solely from a large-scale vortex structure to a small-scale one. Moreover, it demonstrates that passive flow control fails to effectively mitigate aero-optical-induced wavefront aberration. After cooling with jet flow, it is evident that wavefront aberration increases uniformly along the flow direction, as depicted in Case2 (without MVGs). However, when MVGs are added, a series of \"gullies\" appear on the distorted surface due to their arrangement upstream of the window, as an array. The small vortices generated after airflow passes through MVGs affect optical transmission in the downstream flow field, leading to this phenomenon observed in Case11 (\(Ma=3\), jet flow = 0.05 kg/s, with MVGs). It is noteworthy that comparing Case0 (\(Ma=3\), without jet) and Case2 (\(Ma=3\), jet flow = 0.05 kg/s) reveals an overall improvement in wavefront distortion values after incorporating the jet flow. This finding further supports the notion that a significant portion of imaging distortion arises from contributions by mixed layers and turbulent boundary layers. When investigating higher Mach numbers' impact on wavefront distortion with added MVGs, it was found that the aforementioned \"guilly\" phenomenon occurs due to their inclusion--resulting in waveform distortions seen under Case12 (\(Ma=5\), without jet, with MVGs) conditions. As \(Ma\) increases, relative to the results obtained under Case1 (\(Ma=5\), without jet, without MVGs) conditions, there is approximately a 21.7% decrease observed at peak distortions.