# Aerodynamic Window Sealing of a Large-Aperture Channel for High-Power Laser Transmission
## 3 Numerical Simulation  
We used ANSYS software to simulate the motion of gas and dust particles under three different blowing schemes. A larger volume of cylindrical extension domain was added at the channel port to simulate the effect of the external environment on the large-aperture channel. The structure of the large-aperture channel is complex, and the calculation of the flow field and the discrete phase in the channel should be considered. The coupling analysis of high-power laser and flow field will become the focus of future research. To ensure the efficiency and accuracy of the calculation, the finite volume method is used to discretize the computational domain space. At the same time, the SIMPLE algorithm is used to solve the governing equations of each volume element. During the numerical simulation, we assumed that the gas normal and tangential velocities are zero at the fluid-solid interface. Any change in the motion of the gas will not affect infinity. Furthermore, on both sides of the interface of different gases, the gases have equal normal and tangential velocities and stresses. The fluid simulation model of the large-aperture channel is shown in Figure 2. Figure 2 presents a schematic diagram of the model boundary conditions. It can be observed that there are three gas inlets in the channel, and the corresponding faces are set as the velocity inlet boundary. Among them, \(v_{\mathrm{z}}\) indicates the purge gas speed in the axial blowing scheme, \(v_{\mathrm{r}}\) denotes the purge gas speed in the radial blowing scheme, and \(v_{\mathrm{out}}\) indicates the velocity of ambient gas and dust particles. Notably, it is assumed that the velocity of dust particles moving in the environment is equal to the wind speed. In the axial blowing scheme, the \(v_{\mathrm{r}}\) blowing device is removed. The outlet area of the channel is integrated with the cylindrical extension domain, and the bottom surface of the cylindrical extension domain is set as the outflow boundary. The inner wall of the channel is considered the non-slip static wall. The cylindrical surface of the extension domain is set as the symmetry boundary. Suppose that the z-coordinate of the end face of the channel outlet is \(Z_{1}\), the z-coordinate of the monitoring surface is \(Z_{2}\), and the z-coordinate of the end face position at the bottom of the radial blowing is \(Z_{3}\). Accordingly,  
Figure 1: Three blowing scheme models for large-aperture channel sealing. (**a**) The overall structure scheme model; (**b**,**c**) the structure and location of the outlet of the radial blowing scheme. and \(l=Z_{3}-Z_{1}\), where \(L\) denotes the monitoring distance and \(l\) denotes the radial wind distance. The relative position of the coordinates is shown in Figure 2b. The environmental conditions of the numerical simulation are consistent with the experimental, which helps to better compare with the experimental data. The environmental conditions of the numerical model are: (1) The volume flow of purge gas at the outlet of air purification equipment is 0.03 m\({}^{3}\)/s; (2) the wind speed of the external environment is 6 m/s; (3) the mass concentration of the ambient dust particles is 6.32 \(\times\) 10\({}^{-8}\) kg/m\({}^{3}\); (4) the minimum diameter of the ambient dust particles is 0.3 \(\upmu\)m, the maximum diameter is 10 \(\upmu\)m, the average diameter is 1.8 \(\upmu\)m, and the propagation coefficient is 0.553. When comparing different blowing scheme models, the change from the axial to the radial blowing mode is the problem of purge gas volume flow distribution. According to the conditions of axial and radial blowing cross-sectional area and volume flow of purge gas, the value range of axial wind speed \(v_{\rm a}\) is 0-1.6 m/s. Therefore, it can be considered that the radial blowing scheme is \(v_{\rm a}=0\) m/s, the axial blowing scheme is \(v_{\rm a}=1.6\) m/s, and the axial-radial blowing scheme is 0 m/s \(<v_{\rm a}<1.6\) m/s.