# Aerodynamic Window Sealing of a Large-Aperture Channel for High-Power Laser Transmission
## 3 Numerical Simulation
### Prediction of Window Sealing Performance for Axial Blowing Scheme  
As shown in the previous section, when the ambient gas wind speed is 6 m/s, and the dust particle mass concentration is \(6.32\times 10^{-8}\) kg/m\({}^{3}\), the axial blowing scheme effectively seals the large-aperture channel; however, sometimes, high-power laser emission systems are used in harsh environments. Therefore, the design requirement of the aerodynamic window sealing scheme is: that in the environment of seven-force wind (13.9-17.1 m/s) and sandstorm (\(4\times 10^{-3}\) kg/m\({}^{3}\)), the large-aperture channel can resist ambient gas and dust particles entering the sealing area. That is, when the ambient wind speed is less than 18 m/s, and the dust particle mass concentration is less than \(4\times 10^{-3}\) kg/m\({}^{3}\), the minimum non-zero z-directional wind speed of the monitoring surface is \(v_{\mathrm{z}}>0\) m/s at the position where the monitoring distance \(L=100\) mm; and the maximum particle mass concentration \(c=0\) kg/m\({}^{3}\). The axial blowing scheme is used as the aerodynamic window to seal the large-aperture channel. The sealing performance is primarily related to the ambient wind speed and dust particle mass concentration. Therefore, the sealing performance of the axial blowing scheme is predicted from two perspectives. The first: under the assumption that the ambient dust particle mass concentration is \(4\times 10^{-3}\) kg/m\({}^{3}\), the minimum non-zero z-directional wind speed \(v_{\mathrm{z}}\) variation curves with the monitoring distance \(L\) at \(v_{\mathrm{out}}\) of 14 m/s, 16 m/s, 18 m/s, 20 m/s, 22 m/s, and 24 m/s is analyzed as shown in Figure 6. It can be observed that the larger the \(v_{\mathrm{out}}\), the smaller the \(v_{\mathrm{z}}\) at the same monitoring distance position, and the curve stabilizes more slowly. However, at \(L=60\) mm, the \(v_{\mathrm{z}}\) of all curves can fundamentally stabilize in some positive range. At different \(v_{\mathrm{out}}\) values, the pressure distribution at the \(x=0\) mm section position of the large-aperture channel is shown in Figure 7, where Figure 7a illustrates \(v_{\mathrm{out}}=14\) m/s and Figure 7b shows \(v_{\mathrm{out}}=24\) m/s. When comparing the two figures, it is clear that despite the large difference in ambient wind speed, the relative positive pressure can be consistently maintained inside the large-aperture channel to the external environment, and the ambient gas cannot be blown into the deeper position of the channel, but only from channel port around the outflow. Therefore, the larger the \(v_{\mathrm{out}}\), the smaller the pressure at the outlet. Combining Figures 6 and 7, the axial blowing scheme can achieve sealing for the wind speed of 24 m/s or even greater in the sealing area of \(L\geq 100\) mm for the continuous phase of the ambient gas. Second, with \(v_{\mathrm{out}}\) and \(c_{\mathrm{out}}\) as variables, where \(c_{\mathrm{out}}\) denotes the ambient dust particle mass concentration, we analyze whether the axial blowing scheme can achieve the sealing of the discrete phase of dust particles for the area of channel mm under different dust particles velocities and mass concentration environments. Let \(v_{\mathrm{out}}\) be three wind speed levels of 20 m/s, 22 m/s, and 24 m/s, and \(c_{\mathrm{out}}\) be eight mass concentration levels equally divided between \(1\times 10^{-3}\) and \(8\times 10^{-3}\) kg/m\({}^{3}\). The variation curve of the maximum particle mass concentration \(c\) with ambient dust particle mass concentration \(c_{\mathrm{out}}\) at the  
Figure 5: Variation curves of the large-aperture channel sealing indicators for three blowing schemes. (a) The \(v_{\mathrm{z}}\) variation curves with \(L\) for different \(v_{\mathrm{z}}\); (b) the \(c\) variation curves with \(L\) for different \(v_{\mathrm{z}}\).