## 3 Results and Discussion
### Local Force Coefficient  
Figure 11 shows the mean local force coefficient of low-aspect-ratio cylinders in the smooth flow, as well as previous studies, and the value of \(\overline{C}_{D}\) and \(\overline{C}_{L}\) are at 0.5 H of finite length cylinders. For the 2D cylinder [5; 8; 19], a significant \(Re\) effect can be seen. A total of three regimes, subcritical (\(Re\leq\) 2.0 \(\times\) 10\({}^{5}\)), critical (2.0 \(\times\) 10\({}^{5}\) < \(Re\leq\) 4.0 \(\times\) 10\({}^{5}\)), and supercritical (\(Re>\) 4.0 \(\times\) 10\({}^{5}\)), could also be approximately identified according to the curves. However, the \(Re\) effect decreased with decreasing \(AR\) for finite length cylinders due to the three-dimensional flow [1], especially when \(AR\) = 0.323, where almost no \(Re\) effect was observed. For low-aspect-ratio cylinders, the value of \(\overline{C}_{D}\) was smaller than that of \(AR\) = 5.5 [19] and 2D cylinders in subcritical regime, and the variation of \(\overline{C}_{D}\) also did not change as much as other cylinders under the critical regime. However, the extreme value of \(\overline{C}_{L}\) could still be observed, which corresponded to the formation of the separation bubble on one side of the cylinder [40]. The local force coefficients at each height of cylinders varying with \(Re\) are shown in Figure 12. As can be seen in Figure 12a, for M1, the value of \(\overline{C}_{D}\) and \(\overline{C}_{L}\) did not change with \(Re\) = 1.4 \(\times\) 10\({}^{5}\)-2.2 \(\times\) 10\({}^{5}\), indicating that the flow on both sides showed subcritical laminar separation, and that the separation points were in fixed position. With \(Re\) = 2.2 \(\times\) 10\({}^{5}\)-2.6 \(\times\) 10\({}^{5}\), one side went to the critical regime, the separation point moved backward, and the leeward pressure decreased. The other side was also in laminar sep  
Figure 11: The comparison of the mean local force coefficient of circular cylinders in the smooth flow. (**a**) The mean local drag coefficient; (**b**) The mean local lift coefficient. Figure 10: The variation of positive pressure range with \(Re\) under different wind fields. aration. This resulted in a decrease for \(\overline{C}_{D}\), and since the distribution of wind pressure on both sides was asymmetrical, \(\overline{C}_{L}\) increased and reached a maximum at \(Re\) = 2.6 \(\times\) 10\({}^{5}\). With the further increase in \(Re\) = 2.6 \(\times\) 10\({}^{5}\)-4.7 \(\times\) 10\({}^{5}\), the other side also went to the critical regime; while \(\overline{C}_{D}\) was decreasing continuously, the wind pressure on both sides was gradually symmetrical and \(\overline{C}_{L}\) decreased. In the case of \(Re\) = 4.7 \(\times\) 10\({}^{5}\)-5.5 \(\times\) 10\({}^{5}\), \(\overline{C}_{D}\) and \(\overline{C}_{L}\) eventually remained constant under the supercritical regime. Furthermore, by comparing the value at each height of M1, \(\overline{C}_{D}\) and \(\overline{C}_{L}\) in the middle-upper parts of M1 were larger than at other heights. The value of \(C_{ID}\) and \(C_{L}\) is given in Figure 12b. \(C_{L}\) was completely larger than \(C_{ID}\), and had a greater value in the middle-lower part of M1, while \(C_{ID}\) did not change significantly with the height of M1. Meanwhile, \(C_{ID}\) and \(C_{L}\) reached their maximum at around \(Re\) = 2.6 \(\times\) 10\({}^{5}\), corresponding to one side of M1 went to the critical regime. For M2 in Figure 12c, the \(Re\) effect of M2 was not as apparent as that of M1: the value of \(\overline{C}_{L}\) decreased with \(Re\) = 1.5 \(\times\) 10\({}^{5}\)-3.2 \(\times\) 10\({}^{5}\), and then remained stable at nearly 0 while \(\overline{C}_{D}\) was almost unchanged with \(Re\). In addition, \(\overline{C}_{D}\) and \(\overline{C}_{L}\) had a larger value in the middle-upper and middle-lower parts of M2, respectively. The value of \(C_{L}\) decreased with height and reached its maximum at \(Re\) = 1.9 \(\times\) 10\({}^{5}\) (Figure 12d), but \(C_{ID}\) had no significant change with \(Re\) and height.