## 2 Design of the Snow-Wind Combined Experiment Facility
### Introduction of the Main Component  
The facility, as shown in Figure 2, consists of a power section, a flow conditioning section, an experimental section, and a snowfall simulator. Figure 1: (**a**) Photo of the snow–wind combined experiment facility. (**b**) Location of the facility. The power station is the \(3\times 2\) fan-matrix, and the area affected by the model during a snowdrift is thought to be about three times larger than the characteristic length of the model [27]. Therefore, the cross-section of the facility was designed to be \(4.5\times 3.0\) m\({}^{2}\). Considering the fact that there are usually light winds when it is snowing, the facility was designed to be able to produce a stable wind field for a specific duration with a range of speeds from 0.5 to 11.5 m/s. Wind pressure is the main indicator of the output of the fan-matrix and is defined as  
\[P=\frac{\rho k{U_{0}}^{2}}{2}, \tag{2}\]  
where \(P\) is the wind pressure; \(\rho\) is the density of air, and \(\rho\) = 1.395 kg/m\({}^{3}\) when the temperature is \(-20\)\({}^{\circ}\)C; k is the resistance coefficient of pressure of the flow conditioning section, which is defined as the ratio of the outlet area of the facility to the total outlet area of the six airflow fans, and k = 1.734; \(U_{0}\) is the wind speed at the outlet or immediate output from the fan matrix, and \(U_{max}\), which is measured at the section 4 m away from the outlet, is regarded as the available maximal wind speed of the facility and \(U_{max}\) = 11.5 m/s for design purposes. Because the facility is open to the natural environment, a numerical simulation was undertaken to explore the relationship between \(U_{0}\) and \(U\), where \(U\) is the wind speed at the experiment section. Based on the environment of the experimental site, a calculation model of the facility, with a computational domain of \(10\times 10\times 20\) m\({}^{3}\), was formulated. The result showed that when the initial velocity of the wind export of the facility was 15 m/s, the uniform wind speed in the range of 4-20 m was about 11.5 m/s, hence, the value of \(U_{0}\) is approximately equal to 15 m/s. Accordingly, the minimum wind pressure is 272.1 Pa by calculation, and a fan with 286 Pa wind pressure was chosen. The maximum speed measured in the field was 11.5 m/s, which reasonably meets the requirements of the experiments. The flow conditioning section, which stabilizes and smooths the airflow produced by the fan, is a combination of the draft tube, the honeycomb, and the damping net. Two pieces of damping net were stuck on both import and export sections of the honeycomb, and the draft tube served as connection between the power section and the honeycomb. The flow conditioning section was designed to be short to reduce the loss of wind power because of the open experimental environment. Considering the square pattern of the cross-section and the design experience from the wind erosion tunnel designed by [PERSON] [29], a square cross-section with the dimension of \(30\times 30\) mm\({}^{2}\) was chosen as the single unit of the honeycomb with a length of 300 mm. The experimental section is a platform with a circular dial, which is used to fix the model at the required angle. Snowfall suitable for the experiments was not always available, so to accumulate a large amount of data on snow distribution, it was necessary to find a way to simulate snowfall using natural or artificial snow particles. Figure 2: Schematic view of the snow–wind combined experiment facility. In this work, a snowfall simulator situated 1 m away from the wind export was designed to simulate snowfall during the experiments. Before the experiments started, snow, which had been collected in heat-insulation boxes, was placed in a metal box with wire gauze on the bottom. Then, shaking the metal box with an eccentric motor to generate friction between the snow and wire gauze, made snow particles fall from the mesh into the stable wind field caused by the fan-matrix so that a snowfall environment was formed in the test section.