In this study, unsteady RANS simulations are performed to investigate the effect of over-the-wing (OTW) propeller inclination on the aerodynamic interaction with a wing featuring a plain flap. A comparison to experimental data shows that the numerical approach is capable of modeling the wing and propeller separately and can capture the effect of the wing on the propeller in the OTW configuration, but under-predicts propeller-induced flow separation over the flap. The results show that, if the propeller is installed over the flap hinge and aligned with the freestream velocity (baseline configuration), the slipstream and blade tip-vortices generate additional adverse pressure gradients on the wing surface, leading to a local increase in flow separation downstream. However, if the propeller is tilted and aligned with the flap surface (inclined configuration), the slipstream increases the momentum in the boundary layer and the flow remains attached. The propeller alters the pressure distribution of the wing such that higher lift is generated in the baseline case, while a larger drag reduction is achieved in the inclined case. However, combined with the thrust vector of the propeller, the baseline configuration is found to have the largest combined axial force in thrust direction, while the inclined configuration presents the highest effective lift. These results indicate that inclining the propeller can enhance the low-speed performance of OTW distributed-propulsion systems.
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