# Aerodynamic Window Sealing of a Large-Aperture Channel for High-Power Laser Transmission
## 3 Numerical Simulation
### Comparison of Sealing Performance of Three Blowing Schemes  
Since the axial blowing and the radial blowing scheme is fixed, while the axial-radial blowing scheme has a variety of \(l\) and \(v_{\rm a}\) options, it is important to choose the scheme  
Figure 3: Velocity vector of section \(x=0\) mm, and the z-directional wind speed and particle mass concentration of \(L=20\) mm monitoring surface for the large-aperture channel under the three blowing schemes. (**a**) Axial blowing; (**b**) radial blowing; (**c**) axial–radial blowing (\(l=0\) mm, \(v_{\rm a}=1\) m/s).  
with the best parameters in the axial-radial blowing scheme to compare with the other two blowing schemes. Using the control variable method, the effect of the variation of the \(l\) value in the axial-radial blowing scheme on the channel sealing performance is first analyzed. When the axial wind speed \(v_{\rm a}=1\) m/s, the variation curves of sealing indicators for the large-aperture channel with different \(l\) are shown in Figure 4. More specifically, Figure 4 illustrates the \(v_{\rm z}\) variation curves with \(L\) for different \(l\). Evidently, \(v_{\rm z}\) is greater than 0 m/s at \(L>20\) mm in all six curves with different \(l\), indicating that the ambient gas can be stopped from blowing in. When \(L<60\) mm, the \(v_{\rm z}\) of \(l=0\) mm curve is always positive, and when \(L\geq 60\) mm, the curves of different \(l\) tend to be stable and slightly different. Figure 4 presents the \(c\) variation curves with \(L\) for different \(l\). It can be observed that the \(c\) of different \(l\) curves gradually converge to a stable value with the increase of \(L\). At \(L=80\) mm, \(c\) is reduced to zero, so the dust particles can be stopped from blowing in. However, at \(L<80\) mm, the \(c\) of \(l=0\) mm curve is the smallest. Generally, for different radial wind distance \(l\), when the monitoring distance \(L>80\) mm, the large-aperture channel can stop both ambient gas and dust particles from blowing in, thereby achieving a good sealing effect. However, at different monitoring distances, the \(l=0\) mm curve can always maintain \(v_{\rm z}>0\) m/s, \(c\) is minimum, and the curve stabilizes at the fastest rate. Therefore, among the six different \(l\) values, the sealing performance is relatively better when \(l=0\) mm.  
The axial-radial blowing scheme at \(l=0\) mm is considered to compare the sealing performance with the other two blowing schemes. The variation curves of the sealing indicators for the large-aperture channel with different \(v_{\rm a}\) are shown in Figure 5 to better analyze and compare the sealing performance of the three blowing schemes. Figure 5 illustrates the \(v_{\rm z}\) variation curves with \(L\) for different \(v_{\rm a}\). It can be observed that at the same \(L\) position, \(v_{\rm z}\) increases when \(v_{\rm a}\) increases. When \(v_{\rm a}\geq 0.8\) m/s, \(v_{\rm z}\) gradually stabilizes with the increase of \(L\), and they are all greater than 0 m/s after \(L>20\) mm. In other words, the large-aperture channel can achieve the sealing of the ambient gas. Figure 5 depicts the \(c\) variation curves with \(L\) for different \(v_{\rm a}\). It can be observed that \(c\) converges to a stable value faster as \(v_{\rm a}\) increases. When \(v_{\rm a}\geq 0.8\) m/s and \(L\geq 80\) mm, all \(c\) values decrease to 0 kg/m\({}^{3}\). It indicates that the large-aperture channel can achieve the sealing of dust particles. In conclusion, the larger the axial wind speed \(v_{\rm a}\), the better the sealing effect of the large-aperture channel on the ambient gas and dust particles. Therefore, the axial blowing scheme is the best choice for aerodynamic window sealing.  
Figure 4: Variation curves of sealing indicators for the large-aperture channel with different \(l\) when \(v_{\rm a}=1\) m/s. (**a**) The \(v_{\rm z}\) variation curves with \(L\) for different \(l\); (**b**) the \(c\) variation curves with \(L\) for different \(l\).