## 3 Discussions of Experimental Results
### Effect of the Obstruction Factor
It can be seen from Figure 12b and Table 9 that when compared with the OA312 airfoil, the drag coefficients of DCFJ312 airfoils with various \(O\)Fs are significantly decreased, and the drag coefficients are even decreased to negative values at low \(AoA\). As the \(OF\) increases, the drag coefficient of the DCFJ312 airfoil first increases and then decreases. The DCFJ312-OF1/2 airfoil has the smallest drag coefficient and highest lift-to-drag ratio among the three DCFJ312 airfoils. At \(AoA=20^{\circ}\), the drag coefficient decrement of the DCFJ312-OF1/2 airfoil over the OA312 airfoil is 3.8% greater than that of the DCFJ312-OF1/3 airfoil over the OA312 airfoil, and 12.8% greater than that of the DCFJ312-OF2/3 airfoil over the OA312 airfoil. At \(AoA=20^{\circ}\), the lift-to-drag ratio increment of the DCFJ312-OF1/2 airfoil over the OA312 airfoil is 20.9% greater than that of the DCFJ312-OF1/3 airfoil over the OA312 airfoil, and 42.7% greater than that of the DCFJ312-OF2/3 airfoil over the OA312 airfoil. Table 10 shows the moment coefficients of DCFJ312 airfoils with various \(O\)Fs at \(AoA=10^{\circ}\) and \(20^{\circ}\). It can be seen from Figure 12c and Table 10 that when the \(AoA\) is less than \(15^{\circ}\), the absolute value of the moment coefficient of the DCFJ312-OF1/2 airfoil is smallest among the three DCFJ312 airfoils. As the \(OF\) increases, the absolute value of the moment coefficient of the DCFJ312 airfoil first increases and then decreases when the \(AoA\) is greater than \(15^{\circ}\). At \(AoA=10^{\circ}\), the absolute value of the moment coefficient of the DCFJ312-OF1/2 airfoil is decreased by 21.2% when compared with the OA312 airfoil, while that of the DCFJ312-OF1/3 airfoil is increased by 13.1% and that of the DCFJ312-OF2/3 airfoil is increased by 3.0%. At \(AoA=20^{\circ}\), the absolute value decrement of the moment coefficient of the DCFJ312-OF1/2 airfoil over the OA312 airfoil is 30.7% smaller than that of the DCFJ312-OF1/3 airfoil over the OA312 airfoil, and 28.1% smaller than that of the DCFJ312-OF2/3 airfoil over the OA312 airfoil. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Airfoils**} & \multicolumn{2}{c}{\(C_{\mathbf{M}}\)} & \multicolumn{2}{c}{\(\triangle\,\,\mathbf{I}\,\mathbf{C_{M}}^{\dagger}\)} \\ \cline{2-5}  & \(AoA\) = \(10^{\circ}\) & \(AoA\) = \(20^{\circ}\) & \(AoA\) = \(10^{\circ}\) & \(AoA\) = \(20^{\circ}\) \\ \hline OA312 & \(-0.0099\) & \(-0.0310\) & — & — \\ DCFJ312-OF1/3 & \(0.0112\) & \(-0.0156\) & \(13.1\%\) & \(-49.7\%\) \\ DCFJ312-OF1/2 & \(0.0078\) & \(-0.0251\) & \(-21.2\%\) & \(-19.0\%\) \\ DCFJ312-OF2/3 & \(0.0102\) & \(-0.0164\) & \(3.0\%\) & \(-47.1\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Comparisons of moment coefficients of DCFJ312 airfoils with various \(O\)Fs at typical \(AoA\)As. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Airfoils** & \(C_{Lmax}\) & \(\triangle\,\mathbf{C_{Lmax}}\) & \(AoA_{stall}\) & \(\triangle\,AoA_{stall}\) \\ \hline OA312 & \(1.13\) & — & \(22^{\circ}\) & — \\ DCFJ312-OF1/3 & \(1.83\) & \(61.9\%\) & \(34^{\circ}\) & \(12^{\circ}\) \\ DCFJ312-OF1/2 & \(1.89\) & \(67.3\%\) & \(34^{\circ}\) & \(12^{\circ}\) \\ DCFJ312-OF2/3 & \(1.83\) & \(61.9\%\) & \(34^{\circ}\) & \(12^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Comparisons of maximum lift coefficients and stall \(AoA\)s of DCFJ312 airfoils with various \(O\)Fs. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Airfoils** & \(C_{\mathbf{D}}\) & \(\triangle\,\mathbf{C_{D}}\) & \(\mathbf{L/D}\) & \(\triangle\,\mathbf{L/D}\) \\ \hline OA312 & \(0.1819\) & — & \(5.83\) & — \\ DCFJ312-OF1/3 & \(0.1269\) & \(-30.2\%\) & \(9.85\) & \(69.0\%\) \\ DCFJ312-OF1/2 & \(0.1201\) & \(-34.0\%\) & \(11.07\) & \(89.9\%\) \\ DCFJ312-OF2/3 & \(0.1434\) & \(-21.2\%\) & \(8.58\) & \(47.2\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparisons of drag coefficients and lift-to-drag ratios of DCFJ312 airfoils with various \(O\)Fs at \(AoA=20^{\circ}\).