Experimental and Numerical Study on Aerodynamic Characteristics of Distributed Ducted Fans in Ground Effect

The aerodynamic characteristics of distributed electric propulsion (DEP) aircraft change significantly in the near-ground hovering state. In this paper, we employed a combination of experimental and numerical methods to investigate aerodynamic characteristics induced by ground effect for both isolated and distributed ducted fan configurations. The steady-state results indicate that the ground effect significantly influences the outlet pressure of the ducted fan. As the distance to the ground decreases, the thrust contribution from the duct decreases, while the thrust from rotor and stator blades increases, resulting in an overall increase in total thrust. At the distance to the ground of 0.8 D ( D is the ducted fan diameter), the total thrust increases by 3.2% for the isolated ducted fan and by 1.9% for the distributed ducted fans. Steady-state flow analyses further show that the ground effect leads to a decrease in the outlet velocity and a reduction in the effective flow area, thereby lowering the duct thrust. Concurrently, the increased blade angle of attack raises the aerodynamic loads on the rotor and stator blades, enhancing the blade thrust. Transient analyses reveal that for the isolated ducted fan, ground effect induces a tip vortex driven by tip leakage and a ground vortex triggered by shear layer instability, resulting in transient aerodynamic force fluctuations with a standard deviation of 9.1% of the time-averaged thrust. For the distributed ducted fans, aerodynamic interference between fans causes vortex superposition, forming a highly complex three-dimensional vortex structure and leading to a standard deviation in transient force fluctuation as high as 59.9% of the time-averaged thrust.