Asymmetric Duct Design for Directional Airflow Delivery in UAV-Assisted Greenhouse Tomato Pollination

UAV-assisted greenhouse tomato pollination requires lateral airflow delivery toward flower clusters distributed along the crop canopy. To address this, an asymmetric duct was designed to passively redirect the rotor wake through geometric modification of three inner-wall curvature parameters (R1, R2, R3). Three-dimensional CFD simulations were conducted to evaluate the effects of these parameters on airflow redirection and aerodynamic performance. Compared with a conventional symmetric duct, the asymmetric duct shifted the high-velocity wake from a predominantly vertical direction toward the canopy side. Among the three parameters, R3 exerted the greatest influence: increasing R3 from 20 to 65 mm improved the lift-to-drag ratio from 24.7 to 184.2 but reduced the airflow velocity delivered to the pollination region from 6.48 to 2.82 m·s−1. The selected configuration (R1 = 11 mm, R2 = 20 mm, R3 = 25 mm) delivered an airflow velocity of 6.03 m·s−1 at an operating height of 1.44 m, with a lift of 7.04 N and a lift-to-drag ratio of 37.0. These results demonstrate that passive geometric asymmetry can redirect rotor-induced airflow toward the canopy side while balancing airflow delivery, operating height, and aerodynamic performance under greenhouse spatial constraints.