## 3 Experimental Results and Discussion
### Change in the Velocity Field Caused by DBD-PA Actuation  
Under the experimental conditions indicated by the triangular marks in Figures 11-14, the four indices presented in the previous section have relatively large values; therefore, these conditions are selected for the following discussion. Table 2 summarizes the values of \(Re\), \(F^{+}\), and the four indices under these conditions. Figure 16 shows the time-averaged velocity field obtained using the PIV method, and Figure 17 shows the \(C_{p}\) distribution under the same conditions as those in Figure 16.  
Figure 16a,c,f,i show the results without DBD-PA actuation. These results indicate that the boundary layer is separated near the leading edge of the wing, and almost the entire suction side surface of the wing is covered by a recirculation region for (a) \(Re=1.9\)\(\times\)\(10^{5}\), (c) \(4.2\)\(\times\)\(10^{5}\), and (f) \(5.7\)\(\times\)\(10^{5}\). The boundary layer separates once at the leading edge of the wing for (i) \(Re=9.4\)\(\times\)\(10^{5}\); however, the formed separation bubble is very small, and the boundary layer immediately reattaches near the leading edge. Figure 16i also shows that the boundary layer attaches to approximately 20% of the chord length from the leading edge of the wing, where the attached flow region is longer than that under other conditions. These results imply that the boundary layer may be turbulent downstream of the reattachment point [39]. Figure 16: Comparison of PIV results that show changes in flow pattern by DBD-PA actuation. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Re** & \(F^{+}\) & \(K_{CL}\) & \(K_{TKE}\) & \(K_{h}\) & \(\mathbf{ND_{SP}}\) \\ (\(\times 10^{5}\)) & \(F^{+}\) & \(K_{CL}\) & \(K_{TKE}\) & \(K_{h}\) & \(\mathbf{ND_{SP}}\) \\ \hline
1.9 & 1.0 & 0.709 & 3.28 & 0.382 & \(-\)0.005 \\
4.2 & 0.50 & 1.06 & 3.32 & 0.149 & 0.150 \\
4.2 & 10 & 0.511 & 0.778 & \(-\)0.573 & 0.190 \\
5.7 & 1.0 & 1.14 & 1.47 & \(-\)0.115 & 0.145 \\
5.7 & 50 & 0.501 & 0.509 & \(-\)0.383 & 0.190 \\
9.4 & 1.0 & 0.151 & 0.213 & 0.274 & \(-\)0.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Values of \(Re\), \(F^{+}\), and the four indices for the conditions indicated by the triangle marks in Figures 11–14. The other panels in Figure 16 present the typical results with the DBD-PA actuation; the characteristic phenomena can be observed in these figures. For example, Figure 16b presents the result at _Re_ = 1.9 \(\times\) 10\({}^{5}\) with \(F^{+}\) = 1. The shear layer generated by the boundary layer separation at the leading edge shifted slightly toward the wing surface, and the shear layer thickness increased because of DBD-PA actuation. In addition, the TKE in the recirculation region increased significantly. Figure 16d presents the result at _Re_ = 4.2 \(\times\) 10\({}^{5}\) with \(F^{+}\) = 0.5. The trends in change caused by actuation shown in this figure are similar to those in Figure 16b; however, they are emphasized further, i.e., the shear layer thickness increases significantly and the TKE shows a very high value occupying the entire recirculation region. Figure 16e presents the result obtained when _Re_ = 4.2 \(\times\) 10\({}^{5}\) with \(F^{+}\) = 10, and the shear layer clearly shifts toward the wing surface. The recirculation zone cannot be observed in the average velocity distribution in the area between the wing surface and shear layer, and the TKE in the same area increases slightly. Furthermore, the position of the boundary layer separation moved downstream, and no boundary layer separation was observed at the leading edge. Figure 16g shows the results obtained when _Re_ = 5.7 \(\times\) 10\({}^{5}\) and \(F^{+}\) = 1. The shear layer clearly shifted toward the wing surface, and the thickness increased slightly. The TKE in the area overlapping the shear layer also increased. The position of the boundary layer separation moved downstream from the leading edge.