Thrust variations in small rotors due to corner and vertex effects on the ground side

Abstract Thrust changes near walls and the ground plane are influenced by the rotor’s position in indoor flight environments. This study evaluates variations in rotor thrust near a corner, which includes one wall and the ground plane, as well as a vertex, which involves two walls and the ground plane; these phenomena are referred to as the corner and vertex effects, respectively. Additionally, the rotor wake in the vertex effect was visualised using the laser sheet method, and wake velocity was measured with a hot-wire probe. The thrust change in the corner effect on the ground side was minimal, primarily depending on the ground effect. In the vertex effect, thrust decreased to 93% of the thrust outside the vertex effect when the rotor height above ground was 2.5 times the rotor radius, and the rotor was distanced from the two walls by 1.5 times the rotor radius. Flow visualisation and hot-wire velocimetry results suggest that the thrust decrease was caused by the flow recirculation structure between the fountain flow developed along the vertical corner and rotor inflow. The thrust decreases under conditions where the circulation structure appears, and fountain flow velocity accelerates the recirculation. These findings aid in planning the flight path of small multirotors in indoor flight conditions by providing guidance on distances that do not alter rotor thrust near corners and vertices.