## 4 Conclusions  
This study attempted to present the concept of a propeller that injects jets the propeller surface and predict its performance through experiments and computations. Experimental equipment including propellers was directly designed for jet injection, and we performed model tests and computations to compare the results. Experiments were performed with advance coefficients of 0.1 to 0.6, and in the results, it appeared that the thrust and torque decreased for all advance coefficients. When the jet injected, a flow that is induced into the internal structure from the suction side of the propeller occurs, appearing in thrust and torque. However, the jet injection velocity does not reach a higher value than the relative velocity of a propeller in experiment conditions, resulting in relatively reduced thrust and torque. This trend was observed similarly in both the computation and experiment, so it is judged that the result of computations can be reliable. After that, the performance change according to the height of the slit was analyzed through computation. For all slit heights, the thrust tended to increase as the jet injection volume increased. This is the result of changing the pressure distribution on the blade surface due to the Coanda effect when jetting from the blade surface. According to the height of the slit, the pattern of jets injected from the slit was different. When the height of the slit was low, a jet with high speed was injected throughout the slit, and the increase in thrust was high at low \(C_{j}\). However, due to the inject pattern, the moment generated by the jet was small, and the torque reduction was small. When the height of the slit was high, the injected jet was concentrated at high r/R. In addition, the jet concentrated at high r/R led to an effect of increasing the moment arm, resulting in a significant decrease in torque. Also due to wide area of the slit, the jet speed was relatively small, and thus, the power required of the pump was small, resulting in an increase in the efficiency of the propeller, even when considering the efficiency of the pump. Comparing the change in lift and drag according to \(C_{j}\), as \(C_{j}\) increased, the decrease in torque increased, and the increase in thrust decreased. In other words, considering the power of the pump, it can be expected that if \(C_{j}\) is too high, it will not be efficient. The efficiency was compared by identifying thrust with the normal propeller for two cases of thickness. In the case of the NACA66 (MOD, t/c = 0.24) propeller with a relatively high thickness, the volume of the jet required to identify the thrust was small because the curvature of hydrofoil was large. In the case of \(h_{S}\) = 1.0 mm, it was confirmed that the efficiency increases compared to the normal propeller, even when the power of the pump is included. In the case of the NACA66 (MOD, t/c = 0.12) propeller with reduced thickness, the behind side of the hydrofoil has to be cut out due to the inner structure geometry of the hydrofoil, and as a result, the curvature decreased, and the induced downwash flow decreased due to the jet. As a result, the required jet injection volume was increased, but the torque reduction was larger at \(h_{S}\) = 1.0 mm, which greatly increases the efficiency in (MOD, t/c = 0.06) propeller. Through these results, the possibility of improving the efficiency through jet injection on the propeller surface was confirmed. Limitations of this study also exist. The computation results of this study will be less than the expected propeller efficiency when considering the margin or efficiency of the pump. In addition, the jet injection creates region where the pressure drop appears larger than that of the normal propeller in area with high curvature, and the cavitation performance is expected to decrease significantly.