Numerical study on dynamic performance of a ducted fan moving in proximity to ground and ceiling

Ducted fans are widely employed in unmanned aerial vehicles (UAVs) for civil and military uses because they offer low noise and high efficiency. However, dynamic motions in close proximity can disrupt the flow patterns and aerodynamic behaviors of ducted fans, posing a significant stability risk. In this research, numerical simulations were performed using the unsteady Reynolds-averaged Navier–Stokes method and dynamic mesh technique to assess the dynamic performance of ducted fans when rising and descending in proximity effects. The findings reveal that, on the one hand, the rising motion enhances ground effects and diminishes ceiling effects. The thrust losses in ground effect can reach up to 80% of the hovering thrust, while the thrust gains in the ceiling effect can decrease to as low as zero as the translational velocity rises from 1 to 8 m/s. Karman vortex streets are observed in the fan wake at high-speed rise. On the other hand, the descending motion enhances both ground and ceiling effects, leading to increased losses and gains in thrust. The maximum changes account for 63% and 165% of the hovering thrust, respectively. Evolving vortex ring structures are observed during descent. These insights are crucial for optimizing ducted-fan aerodynamic designs and enhancing UAV flight control to ensure safe and efficient operations in varying dynamic conditions.