## 3 Discussions of Experimental Results
### Effect of the Relative Unit Length  
The _OF_ is fixed to 1/2. The DCFJ312-OF1/2 airfoil is selected as the reference to study the effect of the _RUL_. As shown in Figure 13, the _RUL_ of DCFJ rotor airfoil, which is named DCFJ312-OF1/2B, is adjusted from 0.025 (the blocking unit length is 20 mm) to 0.05 (the blocking unit length is 40 mm). Figure 14 shows the aerodynamic coefficient comparisons of DCFJ312 airfoils with various _RULs_. Table 11 shows the maximum lift coefficients and stall _AoA_s of DCFJ312 airfoils with various _RUL_s. It can be seen from Table 11 that the maximum lift coefficient and stall _AoA_ of the DCFJ312-OF1/2B airfoil are smaller than that of the DCFJ312-OF1/2 airfoil. The maximum lift coefficient increment of the DCFJ312-OF1/2 airfoil over the OA312 airfoil is 2.7% smaller than that of the DCFJ312-OF1/2 airfoil over the OA312 airfoil. The stall _AoA_ of the DCFJ312-OF1/2B airfoil is 2\({}^{\circ}\) smaller than that of the DCFJ312-OF1/2 airfoil. Thus, the smaller the _RUL_, the greater the maximum lift coefficient and stall _AoA_. Figure 14: _Cont._  
Figure 13: Injections of DCFJ312 airfoils with various _RUL_s. (**a**) _RUL_ = 0.025; (**b**) _RUL_ = 0.05. Table 12 shows the lift coefficients of DCFj312 airfoils with various \(RUL\)s at \(AoA=10^{\circ}\) and \(20^{\circ}\). Table 13 shows the drag coefficients and lift-to-drag ratios of DCFJ312 airfoils with various \(RUL\)s at \(AoA=20^{\circ}\). It can be seen from Tables 12 and 13 that the \(RUL\) has little effect on the aerodynamic characteristics of the DCFJ312 airfoil. The lift coefficients, drag coefficients and lift-to-drag ratios of DCFJ312-OF1/2 and DCFJ312-OF1/2B airfoils are almost equal at the same \(AoA\), respectively. At \(AoA=10^{\circ}\), the lift coefficients of DCFJ312-OF1/2 and DCFJ312-OF1/2B airfoils are both 25.4% greater than that of the OA312 airfoil. At \(AoA=20^{\circ}\), the lift coefficient increment of the DCFJ312-OF1/2 airfoil over the OA312 airfoil is 3.8% greater than that of the DCFJ312-OF1/2B airfoil over the OA312 airfoil. The drag coefficient decrement of the DCFJ312-OF1/2 airfoil over the OA312 airfoil is 2.2% smaller than that of the DCFJ312-OF1/2B airfoil over the OA312 airfoil. The lift-to-drag ratio increment of the DCFJ312-OF1/2 airfoil over the OA312 airfoil is 0.8% smaller than that of the DCFJ312-OF1/2B airfoil over the OA312 airfoil. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Airfoils** & \(C_{Lmax}\) & \(\triangle C_{Lmax}\) & \(AoA_{stall}\) & \(\triangle AoA_{stall}\) \\ \hline OA312 & 1.13 & — & 22\({}^{\circ}\) & — \\ DCFJ312-OF1/2 & 1.89 & 67.3\% & 34\({}^{\circ}\) & 12\({}^{\circ}\) \\ DCFJ312- & 1.86 & 64.6\% & 32\({}^{\circ}\) & 10\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Comparisons of maximum lift coefficients and stall \(AoA\)s of DCFJ312 airfoils with various \(RUL\)s at \(AoA=10^{\circ}\). Figure 14: Aerodynamic coefficients comparisons of DCFJ312 airfoils with various \(RUL\)s. (**a**) Lift coefficient; (**b**) lift-to-drag ratio; (**c**) moment coefficient. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Airfoils**} & \multicolumn{2}{c}{\(C_{L}\)} & \multicolumn{2}{c}{\(\triangle C_{L}\)} \\ \cline{2-5}  & \(AoA\) = 10\({}^{\circ}\) & \(AoA\) = 20\({}^{\circ}\) & \(AoA\) = 10\({}^{\circ}\) & \(AoA\) = 20\({}^{\circ}\) \\ \hline OA312 & 0.63 & 1.06 & — & — \\ DCFJ312-OF1/2 & 0.79 & 1.33 & 25.4\% & 25.5\% \\ DCFJ312- & 0.79 & 1.29 & 25.4\% & 21.7\% \\ OF1/2B & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Comparisons of lift coefficients of DCFJ312 airfoils with various \(RUL\)s at typical \(AoA\)s.  
Table 14 shows the moment coefficients of DCFJ312 airfoils with various _RULs_ at \(AoA=10^{\circ}\) and \(20^{\circ}\). It can be seen from Table 14 that the moment coefficient of DCFJ312-OF1/2 and DCFJ312-OF1/2B airfoils are almost equal. When compared with the OA312 airfoil, the absolute values of the moment coefficients of DCFJ312 airfoils with various _RULs_ are between 15% and 22%.