# Fast Prediction and Optimization of Building Wind Environment Using CFD and Deep Learning Method
## 3 Results and Discussions
### Optimization of Wind Environment  
This section discusses the overall assessment of the building wind field. Because the mean velocity of the flow field as an evaluation metric is not able to reflect the flow characteristics, we introduced the wind speed acceptable coefficient \(A_{uni}\) as a measure of the quality of the building wind field. The coefficient \(A_{uni}\) is calculated by  
\[A_{uni}=\frac{S_{accp}}{S} \tag{10}\]  
where \(S_{accp}\) refers to the area with the range 0.3 < \(K\) < 1.2 of the acceptable wind speed region, and \(S\) represents the total area of the flow field. In this study, where the dimensionless velocity range is defined as the acceptable wind speed range, a larger \(A_{uni}\) value indicates a higher proportion of uniform wind speed areas in the flow field. Figure 10 compares the \(A_{uni}\) results obtained from CFD simulations and the predictions of the CNN model. It can be observed that the predictions from the CNN model exhibit good consistency with the CFD results, indicating accurate prediction of the details of the building wind field by the model. Figure 10 also demonstrates that different wind speeds lead to varying levels of uniformity in the building wind field. Within the range of 4 m/s to 7 m/s, the uniformity of the building wind field decreases with increasing wind speed. Among the 196 cases studied, the case with the highest uniformity of the building wind field is observed at a wind speed of 4 m/s, a wind direction angle of 90\({}^{\circ}\), and a building spacing of 45 m. On the other hand, the case with the lowest uniformity of the building wind field is found at a wind speed of 7 m/s, a wind direction angle of 90\({}^{\circ}\), and a buildingspacing of 70 m. Under the same incoming wind speed, the uniformity of the building wind field also varies due to changes in the building layout and wind incidence angle. Specifically, at a wind speed of 4 m/s, the variation in the building layout results in the largest difference in the uniformity of the building wind field, \(A_{uni}\), decreases from the highest value of 0.84 to the lowest value of 0.44, representing a 40% reduction in the area of the acceptable wind speed region, which corresponds to a 48% decrease. At a wind speed of 5 m/s, the building wind field uniformity is significantly affected by the building layout, with \(A_{uni}\) decreasing from 0.45 to 0.16. This corresponds to a 29% reduction in the area of the acceptable wind speed region, representing a 64% decrease. Table 2 presents the optimized building layouts under four different incoming wind speeds. The optimal wind direction angle is 90\({}^{\circ}\) at a wind speed of 4 m/s and 0\({}^{\circ}\) at the other three wind speeds. The optimal building spacing for the four wind speeds is 45 m, 50 m, 70 m, and 55 m, respectively. Figure 11 illustrates the dimensionless wind velocity fields of the optimal building layouts at 4 inflow velocities. It can be observed that at a wind speed of 4 m/s, the optimal building layout is in a series arrangement. There is a small area of wind velocity amplification at the windward corner of the front building, and a low-velocity region forms behind the buildings. The downstream buildings are heavily influenced by the wake of the upstream buildings and are almost completely covered by it, resulting in a low-velocity region in the rear. Under the other wind speeds, a parallel arrangement is the optimal layout, where distinct wind velocity amplification and low-velocity regions form at the windward corners and behind the buildings, respectively. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Velocity (m/s)** & **Case** & **H (m)** & **\(\theta\) (\({}^{\circ}\))** & \(A_{uni}\) \\ \hline
4 & A & 45 & 90 & 0.84 \\
5 & B & 50 & 0 & 0.45 \\
6 & C & 70 & 0 & 0.38 \\
7 & D & 55 & 0 & 0.32 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of optimization of building layouts with different inflow wind velocities. Figure 10: Comparison between CFD simulation and model predictions results of \(A_{uni}\).