Numerical simulation of the quadcopter flow field in the vertical descent state

Abstract

Quadcopters will possibly enter the vortex ring state (VRS), which may jeopardize flight safety of the aircraft, in descending as helicopters do. But aerodynamic characteristics of the quadcopter in the VRS are quite different with the helicopter due to the aerodynamic interference between the rotors, and they were hardly studied. In this paper, the flow fields of a quadcopter and a single rotor in vertical descending are studied through CFD simulation, and the variation laws of lift and power are analyzed. The results show that the single rotor and the quadcopter will enter the VRS like helicopters. Compared with the single rotor, the quadcopter enters the VRS at a smaller decent speed (0.65 v h vs. 0.785 v h). The single rotor reaches its largest lift loss at 19.6% in the middle stage of the VRS, while the rotor of the quadcopter reaches it at 10.6% in the late stage. When the quadcopter enters the late stage of the VRS, its lift variation between rotors is up to 5%. For flight safety, the maximum speed of the quadcopter in vertical descending should be limited to a safe speed ( V c = 0.65 v h). This study can provide a reference for the safety of quadcopter flight.