Research of effect of aerodynamic interference between rotors on vortex ring state of quadrotor aircraft

To investigate the impact of the aerodynamic interference among multirotors on the characteristics of vortex rings and their underlying mechanisms, a combination of detached eddy simulation (DES) and overset grid methods to simulate the unsteady aerodynamic load variations of quadrotor aircraft under vortex ring conditions is employed. The results indicate that for the quadrotor drone used in this study, in the early stage of the vortex ring state, due to aerodynamic interference between the rotors, a large-scale circulation structure covering the entire rotor disk is formed. The rotor thrust increases by 17% comparing to the average value of isolated rotors, and the magnitude of unsteady fluctuations decreases by 28%. The aerodynamic interference between the rotors alleviates the adverse effects of the vortex ring state. In the mid-stage, the circulation structure shifts upward and becomes more symmetrical, with the positive effects of aerodynamic interference weakening; however, it still results in a thrust increase of 11% comparing to isolated rotors and a drop of 21% in unsteady fluctuations. In the later stage, the circulation phenomenon above the rotor disk disappears, resulting in a 27% thrust increase comparing to isolated rotors and a drop of 40% in unsteady fluctuations. The interference effects between the rotors accelerate the aircraft's escape from the vortex ring circulation. Aerodynamic interference between the rotors plays a significant role in the performance of the quadrotor drone at different stages of the vortex ring state, particularly showing a remarkable positive effect in the later stage.