## 6 Simulation Analysis and Performance Comparison (Discussion)  
### Shutters' Influence on Side Wing  
The shutter-like fairing structure with the optimized parameters in Table 6 is used under the condition of 15 m/s incoming flow velocity. When the overall negative lift of side wing and shutters increases by 8.5 N (9.7%), the negative lift of side wing increases by 15.61 N (17.6%), the negative lift of the whole vehicle increases by 26.4 N (5.7%), the drag of the whole vehicle increases by 1.136 N (0.51%), the efficiency of side wing increases by 10.1%, and the efficiency of the whole vehicle increases by 4.78%, as shown in Table 7. The comparison of effects before and after the use of shutters can be found in Figures 20-22. As shown in Figure 20, in the original plan, a jet of vortex above the side wing generated by passing through the front suspension linkage is weakened rapidly after installing the shutters, and its influence on the side wing and side wing flaps is weakened. With the decrease in vorticity, the pressure rises, thereby increasing the high-pressure \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \(C_{L}\) & \(C_{L}^{\prime}\) & **Change Rate/\%** & \(C_{D}\) & \(C_{D}^{\prime}\) & **Change Rate/\%** \\ \hline front wing & \(-4.81\) & \(-5.24\) & 8.90 & 0.96 & 0.99 & 3.1 \\ rear wing & \(-2.50\) & \(-2.42\) & \(-3.20\) & 1.24 & 1.22 & \(-1.6\) \\ diffuser & \(-2.82\) & \(-3.26\) & 15.6 & 0.18 & 0.19 & 5.6 \\ side wing & \(-1.87\) & \(-2.2\) & 17.6 & 0.61 & 0.65 & 6.5 \\ vehicle & \(-2.61\) & \(-2.76\) & 5.70 & 1.25 & 1.26 & 0.51 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of coefficients before and after implementing the shutters. Figure 21: Comparison of vorticity at 400 mm offset section plane of vehicle longitudinal symmetrical plane. (**a**) Original condition, the vorticity above the upper surface of side wing is relatively high, that is, in a low-pressure turbulent condition; (**b**) the vorticity on the side wing upper surface is reduced significantly after implementing the shutters, indicating a transition to a more organized flow field. Figure 20: Comparison of vorticity above the side wing. (**a**) Original condition, a jet of strong vortex is generated; (**b**) the strong jet is cut into two weaker parts after implementing the shutters. area in the middle of the upper surface of side wing and the upper surface of side wing flaps. The average pressure is similar, but the high-pressure area increases, as shown in Figure 23. The shutters improve the low-pressure turbulent flow field above the side wing. Specifically, the part close to the side wing surface (including the upper and lower wing surfaces) is transformed into an ordinary flow field, and the average vortex on the upper surface of side wing is reduced from more than 125/s to less than 50/s. The change in flow field of the side wings is extremely small, as shown in Figure 21. Figure 22 shows the velocity vector diagram at the 400 mm offset section of the longitudinal symmetry plane, revealing the role of the leading edge fins and other fins. As shown in Figure 22, the free flow of the leading edge fin of the side wing is smoothly divided into upper and lower parts. The air flow obviously accelerates after passing through the shutters, from less than 4 m/s to about 10 m/s after installing the shutters, thereby filling the speed vacuum area above the upper surface of side wing of the original one. On the one hand, this change greatly reduces the negative pressure area on the upper surface of the front part of side wing. On the other hand, it guides more air to flow under the side wing, strengthening the negative pressure area below the side wing. The two sides work together to enhance the overall negative lift. Figure 23: Surface pressure comparison of side wing. Figure 22: Comparison of velocity at 400 mm offset section plane of vehicle longitudinal symmetrical plane.