Numerical analysis on the ducted propeller aerodynamics in sidewall-ground effect

Owing to their compact structure and robust protective features, unmanned aerial vehicles (UAVs) equipped with ducted propellers are particularly suited for search and detection missions in confined environments. However, in such spaces, proximity effects can lead to pronounced instability in the aerodynamic performance of the UAV, particularly under the influence of multiple wall interactions. This study employs a sliding mesh technique and the Unsteady Reynolds-Averaged Navier-Stokes method to perform computational fluid dynamics simulations, analyzing the ground-sidewall effect's impact on ducted propeller aerodynamic performance across various hovering positions. Research shows that sidewall effects remain largely unaffected by ground effects. However, when the ground height is less than 2r and the sidewall distance is less than r, the ground effect noticeably alters the strength of the sidewall effect. In this region, sidewall suction effects increase sharply as ground height decreases; however, once the ground height falls below 1r, the mean side force diminishes rapidly. Based on the simulation results, this study proposes an empirical formula for side force under coupled sidewall-ground effects, with a mean absolute percentage error of approximately 10% compared to simulation results. Through an analysis of the unstable motion of vortex structures, this study further explains the causes of substantial transient force fluctuations observed near the walls. The findings of this study provide theoretical guidance for the design of flight controllers and the planning of safe flight paths in confined environments.