The coupling effects of internal/external flow has a significant impact on the aerodynamic performance of the distributed ducted fan.In order to further reveal the aerodynamic performance and mechanism of the internal/external flow coupling effect during the climbing and cruising of the distributed ducted fan

this problem was discussed in detail through three-dimensional RANS (Reynolds-averaged Navier-Stokes) numerical simulation and experimental methods. Results showed that the rotor blades and lip affected the thrust significantly in different flight conditions. With the increase of dimensionless mass flow rate

the rotor inlet flow direction changed from negative angle of attack to positive angle of attack

and the thrust coefficient increased. There was an optimal air angle of attack

resulting in highest aerodynamic efficiency in the climbing condition. At cruising condition state

the lip friction resistance was the least and the propulsion efficiency was the highest. Either larger or smaller dimensionless mass flow rate could increase the frictional resistance and differential pressure resistance of the lip wall

thereby reducing the propulsive efficiency.