## 3 Experimental Results and Discussion
### Mechanisms for Increasing Lift Using DBD-PA Actuation  
The two mechanisms of increase in the lift with DBD-PA actuation are assumed to explain all appearances of the three flow phenomena for the increase in \(C_{L}\) and the three trends for the changes in \(C_{p}\) distribution that contributed to the increase in \(C_{L}\) in the present experiment.  
In the first mechanism, the DBD-PA sheds high-energy vortices with a very low pressure area at the center of the vortex into shear flow on the suction side of the wing. Enhancing the low pressure on the suction side of the wing reduces a downward force as integrating pressure over a surface. The vortex with a very low pressure area rolled downstream with the flow on the suction side, causing an increase in \(C_{L}\). The low pressure area explains the first phenomenon and the first trend. Simultaneously, the TKE of the shear layer is increased by the rolling motion of the vortex, and momentum is transported into the flow near the wing surface, corresponding to the enhanced mixing between the recirculation region and freestream. Consequently, an increase in \(C_{L}\) occurs with velocity recovery above the wing. This increase in TKE caused by the high-energy vortex explains the second phenomena and the second trend.  
The second mechanism involves introducing a disturbance into the boundary layer at the leading edge of the wing. This disturbance enhances the laminar-turbulent transition of the boundary layer [66], and it makes the attached distance of the turbulent boundary layer longer than that of the laminar boundary layer, thereby increasing \(C_{L}\). This increase in the attached distance explains the third phenomenon and the third trend. Simultaneously, the turbulent boundary layer causes an increase in the TKE of the shear layer and promotes momentum transport from the mainstream to the flow near the wing surface, increasing \(C_{L}\). This increase in the TKE caused by the disturbance in the boundary layer explains the second trend and second phenomena. These descriptions of the two mechanisms do not contradict the discussion based on Figures 11-17. These descriptions are indeed consistent with the independence of the trends discussed in Section 3.5.  
Considering the relationship between the results in Figures 13 and 17, an increase in \(C_{p}\) on the pressure side of the wing occurs when the ratio of the shear layer height is relatively large. In other words, this result implies that an increase in circulation around the wing can occur despite the absence of momentum recovery in the shear flow on the suction side of the wing. The abovementioned mechanisms cannot explain these results; thus, a third mechanism exists.  
[PERSON] et al. investigated the effect of DBD-PA actuation on a low \(Re\) number of \(6.3\times 10^{5}\) via numerical analysis [61; 67]. They found a two-dimensional strong vortex with a large size and a small disturbance related to the unstable mode of the shear layer as the lift increase mechanism, corresponding to the first and second mechanisms explained above in this section, respectively. Moreover, they proposed a third mechanism, momentum injection by induced flow; however, the applicability of this mechanism was not confirmed for a flow with a high Reynolds number or with the burst actuation of DBD-PA, as in the present experiment, because the effect of momentum injection by the induced flow appears significant only when the velocity ratio of the induced flow by DBD-PA actuation to the mainstream is relatively large, as in the case of the continuous-mode actuation of DBD-PA. Thus, further investigation is required to clarify this third mechanism.