## 3 Reynolds Number Effects on Static Aerodynamic Characteristics  
### Mean Aerodynamic Force Coefficients  
Aerodynamic force coefficients are dimensionless parameters that describe wind loads and provide an intuitive representation of the overall forces acting on the model. The drag coefficient \(C_{\mathrm{D}}\), lift coefficient \(C_{\mathrm{L}}\), and pitching moment coefficient \(C_{\mathrm{M}}\) of the main beam are expressed as follows:  
\[C_{\mathrm{D}}=\frac{2F_{\mathrm{D}}}{\rho L^{2}B} \tag{3}\]  
\[C_{\mathrm{L}}=\frac{2F_{\mathrm{L}}}{\rho L^{2}B} \tag{4}\]  
\[C_{\mathrm{M}}=\frac{2M_{\mathrm{M}}}{\rho L^{2}B^{2}} \tag{5}\]  
where \(\rho\) represents the air density, \(U\) represents the mean wind speed, \(F_{\mathrm{D}}\) represents drag, \(F_{\mathrm{L}}\) represents lift, \(M_{\mathrm{M}}\) represents the pitching moment, and \(B\) represents the width of the main beam cross-section. By integrating the local pressure on the surface of the main beam, the overall drag \(F_{\mathrm{D}}\), lift \(F_{\mathrm{L}}\), and pitching moment \(M_{\mathrm{M}}\) per unit length are obtained. Figure 3: Model installation diagram. Figure 4 shows the variations in the mean aerodynamic force coefficients of the static main beam with respect to the Reynolds number. As shown in Figure 4, the drag coefficient has an obvious Reynolds number effect. In the Reynolds number range of 1.6 \(\times\) 10\({}^{4}\) < \(Re\) < 4.3 \(\times\) 10\({}^{4}\), the drag coefficient decreases significantly upon increasing the Reynolds number. At \(Re\) = 1.6 \(\times\) 10\({}^{4}\), it is around 0.44, and at \(Re\) = 4.3 \(\times\) 10\({}^{4}\), it is around 0.38, which is a reduction of 0.06 or approximately 14%. In the range of 4.3 \(\times\) 10\({}^{4}\) < \(Re\) < 1.2 \(\times\) 10\({}^{5}\), the drag coefficient remains relatively stable upon increasing the Reynolds number, maintaining a value between 0.38 and 0.39. The change law of the drag coefficient is the same as that obtained by other scholars, with only minor numerical differences [9; 12; 19; 23], which indicates that this study is credible. As shown in Figure 4, the lift coefficient is negative across the range of Reynolds numbers tested, indicating that the overall force on the main beam is directed downward. This is similar to the results obtained by [PERSON] et al. [14] and [PERSON] et al. [19] but different from the results obtained by [PERSON] et al. [12], which may be caused by different factors, such as the aerodynamic shape, the wind attack angle, and the Reynolds number. The lift coefficient exhibits a weak Reynolds number effect. In the range of 1.6 \(\times\) 10\({}^{4}\) < \(Re\) < 8.0 \(\times\) 10\({}^{4}\), the lift coefficient slightly increases with the Reynolds number by approximately 0.01. In the range of 8.0 \(\times\) 10\({}^{4}\) < \(Re\) < 1.2 \(\times\) 10\({}^{5}\), the lift coefficient does not significantly change upon increasing the Reynolds number. As shown in Figure 4, the pitching moment coefficient does not change significantly upon increasing the Reynolds number, indicating that the main beam's pitching moment coefficient is unaffected by the Reynolds number. Overall, within the range of Reynolds numbers tested, the drag and lift coefficients of the main beam show a Reynolds number effect. As the Reynolds number increases, the drag coefficient decreases significantly, whereas the lift coefficient increases slightly. The pitching moment coefficient remains unaffected by the Reynolds number. The drag coefficient is positive, and the lift coefficient is negative, indicating that the main beam experiences drag in the backward direction in the crosswind direction and lift in the downward direction. The results show that there is a Reynolds number effect on the mean aerodynamic force coefficients of the static beam and reveal the laws of variation with the Reynolds number, which provides a reference for relevant research of the mean aerodynamic force coefficients.