## 3 Experimental Results and Discussions
### Aerodynamic Force  
The aerodynamic force can be obtained by integrating the surface pressure distributed around the SBG model. Afterward, the lift coefficient (\(C_{l}(t)\)), drag coefficient (\(C_{d}(t)\)), and the moment coefficient (\(C_{m}(t)\)) are calculated by Equation (5).  
\[C_{l}(t)=\frac{F_{l}(t)}{\frac{1}{2}\rho\mathcal{U}_{0}{}^{2}B},\ C_{d}(t)= \frac{F_{d}(t)}{\frac{1}{2}\rho\mathcal{U}_{0}{}^{2}B},\ C_{m}(t)=\frac{F_{m}(t )}{\frac{1}{2}\rho\mathcal{U}_{0}{}^{2}B^{2}} \tag{5}\]  
where \(F_{l}(t)\), \(F_{d}(t)\), and \(F_{m}(t)\) are the time-variant of the lift, drag, and moment force, respectively.  
The aerodynamic coefficients that are acting on the SBG model that are equipped with and without control are displayed in Figure 5. The mean value of the drag coefficient of the case where \(J_{sj}=0\), which was consistent with the experimental results of 0.064 that were presented by [PERSON] et al. [28], 0.061 by [PERSON] et al. [9], and the numerical simulating result of 0.060 given by [PERSON] [29], was obtained as 0.062. With the increase of the \(J_{sj}\), both the mean value of the drag and lift coefficient shows a decrease at first and then an increase. However, the mean value of the moment coefficient of the controlled case maintained a closing value that was slightly large than the case where \(J_{sj}=0\), indicating that the different \(J_{sj}\) can not influence the moment force that is acting on the SBG model. Note that the main reason for the wind-induced vibration on the main girder is a large fluctuation of the aerodynamic force. The results of the fluctuation of the drag, lift, and moment coefficients that are acting on the SGB model with different \(J_{sj}\) are displayed in Figure 5d-f, respectively. The fluctuation of the aerodynamic coefficients were descending at first and then ascending with the increasing of \(J_{sj}\). Therefore, an optimal \(J_{sj}\) for alleviating the unsteady aerodynamic force that is being exerted in the SBG model is required. This saturation phenomenon was also found by [PERSON] et al. [20], [PERSON] et al. [27], and [PERSON] et al. [30]. When the \(J_{sj}\) equals 0.0094, the best control ability was possessed in the present investigation. The control effect for the drag, lift, and moment coefficient fluctuation was 16.23%, 36.34%, and 38.74%, respectively. That conclusion agreed well with the results of the surface pressure analysis.  
Figure 6 gives the time series and the power spectral density analysis of the lift coefficient being exerted in the SBG models with and without the trailing edge jets. The lift coefficient when \(J_{sj}=0\) shows a significant fluctuation during the experiment, as shown in Figure 6a. When the trailing edge jets were conducted in the SBG model with \(J_{sj}=0.0094\)  
Figure 5: Aerodynamic forces that are acting on the SBG model. The mean value of the drag coefficient (**a**), lift coefficient (**b**), and moment coefficient (**c**). The fluctuation of the drag coefficient (**d**), lift coefficient (**e**), and moment coefficient (**f**).  
the fluctuation of the lift coefficient was reduced compared to the case \(J_{sj}=0\). The peak value of the reduced frequency for the case \(J_{sj}=0\) was obtained to be 0.285 based on the fast Fourier transform (FFT) analysis, which was similar to that of 0.28 that was presented by [PERSON] et al. [28] and [PERSON] et al. [18]. The amplitude of power spectral density analysis of the case \(J_{sj}=0.0094\) was lower than that of the case \(J_{sj}=0\), and the peak value of reduced frequency of the lift force was also changed to 0.279, given in Figure 6b. This indicates that the trailing edge jets that were equipped in the SBG model can modify the frequency and the strength of the vortex shedding behind the test model.