Thrust Characteristics of a Ducted Fan of a Quadcopter in Various Flight Modes

Ducted fans are widely used in vehicles with a high engine power per unit swept area, including hovercraft propulsors and vertical take-off aircraft. Computational fluid dynamics (CFD) is a powerful tool for selecting the aerodynamic configuration of new aircraft and engines and for determining their optimal operating conditions. The full Navier–Stokes equations, closed by the Shear Stress Transport (SST) and Spalart-Allmaras (SA) turbulence models, are used to simulate airflow induced by the rotating blades of quadcopter ducted-fan propulsors. Thrust characteristics of the ducted fan are analyzed based on numerical simulations in different flight modes, such as hovering and oblique inflow. Tip clearance and inner-wall effects on thrust and power are reported. For the studied four-blade ducted fan, varying the blade angle of attack from 16∘ to 32∘ raises the thrust coefficient from 0.27 to 0.84 and the power coefficient from 0.18 to 0.50. At a constant shaft power of 3750 W, the optimal relative tip clearance for moderately loaded blades is 1.5% (16∘ angle). For heavily loaded blades (32∘ angle), maximum thrust occurs at zero clearance. However, even at 0.8% clearance, losses are less than 0.1% compared to the closed-tip configuration. For technological reasons, a small clearance is generally preferred.