Numerical study of coupled sidewall–crosswind effects on hovering unmanned aerial vehicle rotors

The aerodynamic stability of unmanned aerial vehicles (UAVs)operating in urban environments is critically challenged by the sidewall effect and crosswind disturbances. This study numerically investigates the unsteady aerodynamic response of a hovering rotor subjected to the influence of a vertical sidewall and crosswind. Under the influence of the sidewall, results indicate that the sidewall induces a distinct asymmetry in lateral aerodynamic characteristics, while the axial thrust and torque remain relatively insensitive to wall proximity. A significant wall-directed lateral aerodynamic response emerges when the non-dimensional wall distance (d/r) falls below 0.6, which is attributed to the premature dissipation of the wall-side tip vortex. The introduction of crosswind (0–20 m/s) at a critical proximity of d/r = 0.2 fundamentally alters the flow field. Increasing crosswind velocity significantly amplifies the unsteady fluctuations of the aerodynamic response, while concurrently reducing the mean torque magnitude. Flow field analysis reveals that this dynamic load response originates from the distinct spanwise asymmetry of the wake evolution. The crosswind and the sidewall drive a lateral deflection of the rotor hub wake and trigger strong mutual induction between tip vortices. The findings of this study offer theoretical insights for ensuring the operational safety and stability of UAVs in urban environments.