## 3 Results
### Comparison with Normal Propeller
#### 3.3.1 NACA66 (MOD, t/c = 0.24) Propeller  
By adjusting the jet injection volume for the height of each slit, the difference from the thrust produced by the normal propeller was identified within 1%. Table 7 shows a comparison between the computation results of the normal propeller and the change in performance after and before jet injection of the Coanda propeller. A comparison of the propeller performance changes through jet injection showed an increase in thrust and a decrease in torque at \(h_{S}\) = 1.0 mm and \(h_{S}\) = 0.6 mm, similar to the previous results. At \(h_{S}\) = 0.6 mm, the efficiency increased by about 1.7% compared to the efficiency of the normal propeller. However, when \(h_{S}\) = 0.2 mm, the thrust increased, but the torque also increased. The reason for this result is that the thrust that have to be increased to identify the normal propeller is small, so the thrust can be identified even with a low injection volume. Therefore, the increase of the blade surface torque caused by the jet is larger than the moment generated by the jet. However, in the case of \(h_{S}\) = 0.6 mm, the thrust increases, and the torque decreases, as in the case of \(h_{S}\) = 1.0 mm, but \(\Delta K_{T}/C_{j}\) is the lowest compared to other propellers. As a result, the required power of the pump was also the largest, and the efficiency of the propeller was reduced the most. In order to inject a jet and increase the thrust by the Coanda effect, it is necessary for the jet speed to be higher than the relative speed of the propeller. From the previous results, it was confirmed in Figures 7 and 10 that the thrust decreases when the jet velocity is less than the propeller's inflow velocity. Looking at Table 7 and Figure 20a, it can be seen that the jet velocity is injected faster the relative velocity of the propeller even at low \(C_{j}\) when \(h_{S}\) = 0.2 mm, and it is injected all over the slit. That is, the area of the slit is small, and it is easy to increase the speed of the jet, so the effect of improving the thrust through the jet can be seen even at al low injection volume. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline _Type_ & \(C_{j}\) & \(K_{T}\) & \(\Delta K_{T}/C_{j}\) & \(10K_{Q}\) & \(\Delta 10K_{Q}/C_{j}\) & \(in\)(kg/s) & \(V_{jet}\)(m/s) & \(P_{\mathrm{pump}}\)(W) & \(\eta_{0}\) \\ \hline Normal & - & 0.073 & - & 0.087 & - & - & - & - & 0.534 \\ \hline \(h_{S}\) = 1.0 mm & 0.034 & 0.073 & 0.505 & - & 0.077 & - & - & - & 0.454 \\  & 0.034 & 0.073 & 0.505 & 0.057 & \(-\)0.602 & 0.55 & 5.69 & 8.94 & 0.543 \\ \hline \(h_{S}\) = 0.6 mm & 0.0 & 0.060 & - & 0.079 & - & - & - & - & 0.487 \\  & 0.030 & 0.073 & 0.408 & 0.073 & \(-\)0.181 & 0.40 & 6.89 & 9.54 & 0.446 \\ \hline \(h_{S}\) = 0.2 mm & 0.0 & 0.063 & - & 0.079 & - & - & - & - & 0.507 \\  & 0.013 & 0.073 & 0.809 & 0.081 & 0.184 & 0.15 & 7.77 & 4.56 & 0.487 \\ \hline \end{tabular}
\end{table} 
Table 7: Performance comparison of Coanda propeller with thrust identify of normal propeller (NACA66 (MOD, t/c = 0.24)). Figure 20: Comparison of changes in hydrodynamic force on the surface of a normal propeller and Coanda propellers (NACA66 (MOD, t/c = 0.24)). However, in the case of \(h_{S}\) = 1.0 mm and \(h_{S}\) = 0.6 mm with high slit height, it can be expected that there is an injection volume range in which the thrust decreases because the jet velocity is less than the relative velocity of the propeller. In the case of \(h_{S}\) = 0.6 mm, as in the case of \(h_{S}\) = 0.2 mm, a jet is injected across the slit to generate thrust. However, looking at Figure 20a, jet injection hardly occurs around r/R = 0.5. That is, in the case of \(h_{S}\) = 0.6 mm, the propeller efficiency is the lowest at low \(C_{j}\), because the slit area is relatively large, and the additional injection volume is required to increase the jet injection speed at low r/R.