## 3 Experimental Results and Discussion
### Change in the Velocity Field Caused by DBD-PA Actuation
Figure 16h shows that the shear layer shifts further toward the wing surface than in Figure 16g and at _Re_ = 5.7 \(\times\) 10\({}^{5}\) with \(F^{+}\) = 50, whereas the increase in TKE is smaller than that in Figure 16g. Similar to Figure 16e,g, the boundary layer separation at the leading edge was prevented. Figure 16j presents the result obtained for _Re_ = 9.4 \(\times\) 10\({}^{5}\) with \(F^{+}\) = 1. The position of the shear layer moved slightly away from the wing surface with DBD-PA actuation in a different manner from the other conditions with a low _Re_ number. The TKE of the shear layer increased, similar to that under the other conditions. The figure also indicates that the separation point of the boundary layer hardly changes, suggesting that DBD-PA has little effect on the enhancement of momentum exchange and separation suppression in the turbulent boundary layer in high-Reynolds-number conditions. Figure 17 shows \(C_{p}\) distributions on the wing surface under the same conditions as those shown in Figure 16. The red arrows in this figure denote the separation point of the boundary layer, i.e., the starting position of the recirculation region evaluated based on the PIV results. Without actuation, a flat distribution was observed in most areas on the suction side surface with a negative \(C_{p}\) because the flow separates, and a separate area with recirculation is formed in the downstream region of the separation point on the suction side surface. The upstream edge of the flat region indicates the separation point; therefore, the flow is separated at the leading edge, as shown in Figure 17a _Re_ = 1.9 \(\times\) 10\({}^{5}\), (b) 4.2 \(\times\) 10\({}^{5}\), and (c) 5.7 \(\times\) 10\({}^{5}\), and the separation point moves downstream, as shown in Figure 17d 9.4 \(\times\) 10\({}^{5}\). The change in the \(C_{p}\) distribution with DBD-PA actuation was characterized by considering the relationship between the three indices shown in Figures 12-14 and the \(C_{p}\) distributions shown in Figure 17. Three trends of change correspond to the three phenomena described in the previous sections. Figure 17: \(C_{p}\) distribution on the wing model surface with changes in flow pattern by DBD-PA actuation on each _Re_ number. The first trend is observed in the cases of Figure 17a with \(F^{+}\) = 1, (b) \(F^{+}\) = 0.5, and (c) \(F^{+}\) = 1.0, in which a large increase in the TKE is observed in Figure 12. Under these conditions, the negative \(C_{p}\) was enhanced over the entire chord of the suction side surface of the wing. In contrast, the distribution did not exhibit a negative \(C_{p}\) peak at the leading edge. This result corresponds with the first phenomena. The DBD-PA actuation shed high-energy vortices on the suction side surface of the wing, contributing to the growth of the negative \(C_{p}\) on it. The second trend was observed under all conditions with DBD-PA actuation, as shown in Figure 17, in which the pressure coefficient increased on the pressure side of the wing. This result indicates an increase in circulation around the wing by DBD-PA actuation. All the results cannot be explained in this study; however, one reason for this increase is that the DBD-PA actuation increases the momentum in the flow near the wing by attracting a shear layer to the wing surface, as shown in Figure 13. The increase in \(C_{p}\) at the trailing edge suggests a reduction in the recirculation region in the wake caused by momentum recovery on the wing surface. Furthermore, the prominent variation on the pressure side was considered affected by the second phenomenon; however, further research that considers the relationship between the changes in the pressure side \(C_{p}\) distribution and the trailing edge flow field is necessary to fully clarify the mechanism behind this trend.