## 3 Results and Discussion
The mass of particles blown off from the target building in case \(D/H0=1\)--\(H/H0=2\)--\(WD\)\(0^{\circ}\) is the least amongst all wind tunnel tests, which is around 33% of \(m0\). An interesting phenomenon is observed that there are two erosion areas on both sides of the target building, and the eroded area decreases first and then increases instead of decreasing all the time with the increase of the height of the interfering building. Generally speaking, the snow distribution on the roof of the target building tends to be more uniform when the interfering building is positioned upstream of the target building. It can be seen from Figure 6 that when the wind direction is \(90^{\circ}\), the interfering building is positioned at the side of the target building; the friction velocity on the target building significantly increases due to the interference. It results in a more eroded area on the target building, and the snow distribution on the target building roof tends to be more uneven. The part of the target building roof near the interfering building is seriously eroded, and particles are blown to the center of the target building and then accumulated, leading to a larger snow depth at the position where \(x/L\) is around 0.5 when compared with the isolated case, such as case \(D/H0=1\)--\(H/H0=1\)--\(WD\)\(90^{\circ}\) and case \(D/H0=2\)--\(H/H0=1\)--\(WD\)\(90^{\circ}\). However, the part of the target building away from the interfering building is not affected. Thus, the snow distribution of the crosswind direction is seriously uneven; hence, the snow layer on the target building for the 90-degree cases is highly three-dimensional. With the increase of the height of the interfering building (\(H\)), the interference effect becomes more powerful, and according to Figure 6d, more particles are blown off the target building roof. The mass of particles blown off from the target building in case \(D/H0=1\)--\(H/H0=2\)--\(WD\)\(90^{\circ}\). However, the part of the target building away from the interfering building is not affected. Thus, the snow distribution of the crosswind direction is seriously uneven; hence, the snow layer on the target building for the 90-degree cases is highly three-dimensional. With the increase of the height of the interfering building (\(H\)), the interference effect becomes more powerful, and according to Figure 6d, more particles are blown off the target building roof. The mass of particles blown off from the target building in case \(D/H0=1\)--\(H/H0=2\)--\(WD\)\(90^{\circ}\) is the least among the two cases. Figure 5: Experiment results of cases under the \(0^{\circ}\) wind direction: (**a**) building spacing: \(D/H0=1\); (**b**) building spacing: \(D/H0=2\); (**c**) building spacing: \(D/H0=3\); (**d**) normalized mass of particles blown off the target building. 1--\(H/H0\) = 4--\(WD\) 90\({}^{\circ}\) is the heaviest amongst all the wind tunnel tests, which is 2.67 times that of the case isolated. In this case, the normalized snow depth of the central line shows two peak values, and both the peak values are lower than 0.4. With the increase of the building spacing, the disturbance of the interfering building is weakened, fewer particles are blown off the target building roof, the snow distribution on the target building roof becomes more similar to that of the isolated case, and the form of the normalized snow depth changes from a bimodal distribution to a single peak distribution, as shown in Figure 6.  
It can be seen from Figure 7 that when the wind direction is 180\({}^{\circ}\), the interfering building is positioned downstream of the target building, and the flow separation form of the target building is unchanged; hence, the form of the snow distribution on the target building is nearly the same as the isolated case. However, the wind velocity of the target building is somewhat lower than the isolated condition because the wind is blocked by the interfering building; hence, the normalized snow depths are slightly amplified compared to the isolated case.