Research on Ground Effect of Ducted Fans of VTOL UAVs

In recent years, ducted fans, as a kind of propeller with excellent performance, have been widely used in various vertical take-off and landing(VTOL) unmanned aerial vehicles(UAVs). However, there is less research on its ground effect in China. Therefore, in this paper, a solution method based on Reynolds mean Navier-Stokes (RANS) equations and multiple reference coordinate system(MRF) was used. Through numerical simulation, the force and torque changes of each part of the ducted fans with three different blade numbers at different elevations were calculated. The changing mechanism of aerodynamic characteristics was analyzed by calculation results of computational fluid dynamics. The results show that when the altitude near the ground reaches a certain value, the aerodynamic characteristics of the ducted fans change significantly. The lift force of the propeller increases, but that of the duct decreases, and the reverse torque of the whole system increases, which were finally quantified as the variation of lift coefficient, power coefficient, and quality factor. The power coefficient increases significantly with the decrease in the elevation, and the variation of lift coefficient and quality factor of the ducted fans is related to the number of propeller blades. A preliminary conclusion on the influence of ground effect on the aerodynamic characteristics of ducted fans is thus obtained.