## 3 Experimental Results and Discussions
### PIV Measurement Results
The eigenvalues and the eigenvectors of the autocovariance matrix can be obtained. Afterwards, the accumulative energy proportion of  
Figure 7: A time-averaged representation of the flow field behind SBG model. (**a**) \(J_{ij}=0\), (**b**) \(J_{ij}=0.0016\), (**c**) \(J_{ij}=0.0094\), (**d**) \(J_{ij}=0.0409\), \(J_{ij}=0.0802\), and (**f**) \(J_{ij}=0.0094\). (**a**–**e**): plane II, (**f**): plane I.  
each POD mode can be calculated by the eigenvalues of the autocovariance matrix, and the POD modes can be constructed from the basis built up from the snapshots. Figure 9 shows the percentage of the accumulative contribution of every POD mode to the total turbulence kinetic energy of the flow field for the different test cases in PIV measurement. It is observed that the first two POD modes possess 64.6% of the total energy for the case \(J_{yi}=0\). The first two POD modes represent the large-scale coherent structure, and the high-order POD modes represent the small-scale coherent structure as given by [PERSON] et al. [37]. Therefore, the large-scale coherent structure plays an important role in the wake flow behind case \(J_{yi}=0\). When the control method is applied in the SBG model, the energy of each POD mode that is exhibited immensely changes. The total energy of the first two POD modes is slightly decreased, as \(J_{yi}\) is set as 0.0016, indicating that a little strength of the jet flow cannot significantly influence the vortex. The ratio of the energy of the first and second POD modes to the total kinetic energy for cases \(J_{yi}=0.0016\), \(J_{yi}=0.0094\), \(J_{yi}=0.0409\), and \(J_{yi}=0.0802\) are 62.0%, 33.8%, 53.3%, and 53.2%, respectively. Hence, the total energy of the first two POD modes decreases at first and then increases, as shown in Figure 9 when \(J_{yi}\) improves. Moreover, the small-scale coherent structures in the wake flow field behind case \(J_{yi}=0.0094\) occupy most of the energy for the global flow structure, which alleviates the large amplitude of the unsteady aerodynamic force that is being exerted in the SBG model compared to the case \(J_{yi}=0\). Figure 8: Instantaneous vortex shedding behind SBG model. (**a**) \(J_{yi}=0\), (**b**) \(J_{yi}=0.0094\). Figure 9: The cumulation energy proportion for the various POD modes. To identify the characters of the POD modes, the first five POD modes for cases \(J_{sj}=0\) and \(J_{sj}=0.0094\) are plotted in Figure 10. For the case where \(J_{sj}=0\), the first two dominant POD modes are symmetrical about the line Y/B = 0.02 and exhibit alternating vorticity that is distributed in the wake flow. Nevertheless, modes three to five vary from modes one and two: modes three and four are asymmetrical about the line Y/B = 0.02. There are two rows of counter-rotating vorticity concentrations that are displayed in the flow field behind the case \(J_{sj}=0\) closed to the test model and then changed into the arrowhead structures as the flow field moves downstream, as shown in Figure 10c,d. Moreover, mode five shows some a small-scale vorticity concentration behind case \(J_{sj}=0\). The antisymmetric vorticity flow fields that are calculated by POD represent the symmetric features of the vortex flow field. Conversely, the symmetrical vortex flow structures stand for an antisymmetric flow field, as [PERSON] et al. [38] described. In consequence, modes one and two of the case \(J_{sj}=0\) stand for the large-scale alternating vortex shedding forming the Karman vortex street, while modes three and four denote the small spatial scale vortices with symmetric forms, and mode five represents the irregular distribution of the vorticity structures with small geometric scale. For the SBG model with the trailing edge jets, the flow structures of POD modes show noticeable differences that are in contrast to their counterparts of the uncontrolled case.