## 2 Materials and Methods
### Regime of the Wind Tunnel Test  
Wind tunnel tests were conducted with fine silica sand as the substitute for snow particles in this paper. The physical properties of the snow particles and fine silica are shown in Table 1.  
To study the interference effects of a high-rise building on the snow load on a low-rise building with a flat roof, two models were adopted: one is the interfering building and the other is the target building. The model scale ratio is 1:50, and the size of the target building model is 15 cm \(\times\) 15 cm \(\times\) 8 cm. The influences of the height of the interfering building and the distance between buildings on the snow distribution of the target building under three different wind directions are discussed. A schematic diagram of the wind tunnel tests is shown in Figure 2. The height of the target building is defined as \(H0\), the height of the interfering building is defined as \(H\), and the distance between the target building and the interfering building is defined as \(D\). The interfering building height is set to be 1, 2, 3, or 4 times that of the target building, and the distance between buildings is set to be 1, 2, or 3 times the height of the target building. The length of the wind tunnel is 6m, the section size is 1.2m\(\times\)1m, and the blocking rate of the wind tunnel is less than 5%. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Snow Particles** & **Fine Silica** \\ \hline Density \(\rho_{\text{s}}\) (kg/m\({}^{3}\)) & 250 & 2650 \\ Diameter \(d_{\text{s}}\) (mm) & 0.15 & 0.2 \\ Settling velocity \(W_{f}\) (m/s) & 0.2-1.0 m/s & 0.6 \\ Threshold friction velocity \(u^{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{ \For comparison, a test on the isolated target building was also carried out; hence, there are 3 \(\times\) 4 \(\times\) 3 + 1 = 37 wind tunnel tests in total. First, 9-mm-thick fine silica sand particles are laid on the roof of the target building model before the wind tunnel tests, corresponding to a 0.45-m-thick snow depth for the prototype. If the bulk density of snow is 150 kg/m\({}^{3}\), the snow depth of 0.45 m corresponds to the basic snow pressure in Harbin, China. The wind velocity at the eave height of the low-rise building model is set as 7 m/s, and the profiles of the mean wind velocity and turbulent intensity are shown in Figure 3. The reference height \(H_{\text{ref}}\) is 0.08 m, and the reference wind velocity \(U_{\text{ref}}\) is 7 m/s. The average wind velocity profile follows the logarithmic rate distribution. The friction velocity is 0.21 m/s, and the roughness height is 0.000205 m.  
The parameters of the wind tunnel tests and prototypes are shown in Table 2. The eave height of the target building of the prototype is 4 m, and the time duration of the prototype is 29.1 min. The similarity criteria are listed in Table 3. Due to the limitation of the particle properties, not all similarity criteria are matched. The Reynolds number of the aerodynamic roughness height of the tests \(u_{t}^{*3}/2 gv>30\) maintains the fully developed turbulent flow. The densimetric Froude numbers of the tests are different from that of the prototype. However, [PERSON] (1984) [2], [PERSON] et al. (2014) [11], and [PERSON] et al. (2016) [12] conducted contrast tests of different particles and pointed out that the Froude number has minimal influence on the final pattern of the redistribution of snow. Thus, the similarity parameters \((\rho/\rho_{\text{s}}-\rho)\big{(}u_{t}^{*2}/gd_{s}\big{)}\) and \((\rho_{\text{s}}/\rho_{\text{s}}-\rho)\Big{(}U(H)^{2}/gH\Big{)}\) could be relaxed. The heavy particle requirement similarity parameter \(\rho_{\text{s}}/\rho>600\) is satisfied. The settling velocity of snow particles may range from 0.2-1.0 m/s, thus the similarity criteria \(W_{f}/U(H)\) are satisfied. As mentioned before, the main purpose of this paper was to investigate snow load interference effects rather than reproduce a specific prototype, thus it is acceptable to relax some of the similarity criteria.