Electric vertical takeoff and landing aircraft frequently operate within confined areas in urban environments. This paper investigates the complex interactions induced by a coaxial rotor hovering in proximity to a cubical building model. Simulations were conducted using the Detached Eddy Simulation method and overset mesh, coupled with a high-efficiency hybrid trim model. Various rotor positions over the ground and adjacent to the cubical obstacle were analyzed. Results indicate that the lower rotor experiences greater thrust gain than the upper rotor in ground effect. This is primarily because the blocking effect originates from the ground and diminishes gradually upward. For the lower rotor, ground effect attenuates thrust fluctuations caused by the blade-meeting interaction but amplifies the periodic up-and-down fluctuations. When the rotor hovers adjacent to the obstacle, the sidewall exerts a flow-guiding effect, inducing a high-velocity region near the sidewall and causing blade thrust loss. The rotor–obstacle interaction exhibits two primary effects: a thrust gain resulting from the blocking effect caused by the obstacle-ground corner, and a thrust loss caused by the wake recirculation flow, inducing downwash across the rotor disk. This downwash initially acts on the upper rotor, exerting a dominant thrust loss primarily on the upper rotor rather than the lower rotor. Compared to flat ground, the corner blocking effect is enhanced due to its dual-path blockage in both axial and radial directions. The strengths of the corner blocking effect and the recirculation flow depend on the rotor position relative to the obstacle.
Qi et al. (2025) studied this question.