## 3 Results
### Performance Variation with Slit Height and Jet Injection Volume
Due to hydrofoil geometry and the pattern of the jet, which is displayed differently according to the height of the slit, the tendency of thrust increment also appears differently according to the height of the slit. Comparing the thrust generated at the same \(C_{j}\), when \(h_{S}\)= 1.0 mm, high thrust is concentrated in a narrow at high \(r\)/R, and when \(h_{S}\) = 0.2 mm, it is distributed over the entire slit. When \(h_{S}\) = 0.6 mm with a medium slit height, the thrust appears in the entire slit, and at the same time, the thrust is partially concentrated at high \(r\)/R. Figure 15: Distribution of tangential velocity and thrust PUA according to \(C_{j}\) for each slit height (\(J_{A}\) = 0.4)  
r/R. This can be analyzed by the effect of jet thickness due to the centrifugal force as in the previous case. When \(h_{S}\) = 0.2 mm, the speed of the jet is very high, but the thickness of the jet is thin, so it does not induce a large downwash when flowing on a curved surface. On the other hand, when \(h_{S}\) = 1.0 mm, when jet is thick and flow on a curved surface, the downwash is greatly guided, and high thrust is generated at the same time. Such a tendency appears at the same time even when \(h_{S}\) = 0.6 mm. Therefore, as shown in Figure 14, the thrust is the highest at low \(C_{j}\), because the jet induces the downwash of the entire slit at \(h_{S}\) = 0.2 mm. But the higher the mass flow rate, the greater the amount of induced downwash is at \(h_{S}\) = 0.6 mm and \(h_{S}\) = 1.0 mm because of the jet thickness and large curvature, the thrust is higher than at \(h_{S}\) = 0.2 mm. Figure 16 shows the velocity distribution at the center of the slit for each \(C_{j}\). When \(h_{S}\) = 0.2 mm, it can be confirmed that the velocity change is not largely based on r/R, and the jet with the fastest velocity is injected in the entire slit. However, when \(h_{S}\) = 0.6 mm, the jet is injected over the entire slit like at \(h_{S}\) = 0.2 mm, but there is a flow that is absorbed into the inner structure at low r/R. In addition, due to the centrifugal force generated by the rotation of the propeller, the flow velocity of the jet increases as r/R increases. Similarly, when \(h_{S}\) = 1.0 mm, the velocity change due to r/R appears the largest. A high r/R, a jet with a faster speed is generated compared to \(h_{S}\) = 0.6 mm, and there is a flow that is induced into the inner structure until r/R = 0.6. These jet injection patterns are shown in the same way as \(C_{j}\) increases. Figure 17 shows the change of torque by \(C_{j}\). It can be confirmed that the torque on the blade tended to increase at all slit heights as \(C_{j}\) increased in Figure 17b. However, a large decrease in torque appeared in the inner structure, and the total torque tended to decrease as \(C_{j}\) increased. It can be seen that the jet is injected in the direction opposite to the direction of rotation of the propeller, and a moment is generated in the direction of the rotation of the propeller. Therefore, a decrease in torque appears in the inner structure. The  
Figure 16: Tangential velocity distribution at the center of the slit according to \(C_{j}\) for each slit height. decrease in these torques appeared most at \(h_{\text{S}}=1.0\) mm, and it was analyzed by the jet injection pattern. This phenomenon appeared because the jets are concentrated at high r/R, so the jet moment arm is largest. In Figure 18, the torque PUA distribution by jet injection becomes almost the same as the thrust distribution. Similar to the thrust, behind the slit, a large torque increase is shown when jet injection guides the downwash, and the mass flow is concentrated. The jet injected from the slit generates thrust from the surface of the blade while guiding the downwash by the Coanda effect, and at the same time, higher wall shear stress is generated by the jet, so the distribution of thrust and torque is similar. However, in the case of wall shear stress, the flow near the wall is dominated by the influence of velocity particular.