Experimental Investigation Into The Vortex Ring State Of Multi-Rotor Configurations

Abstract

This paper presents an experimental investigation of the effect of rotor separation on the structure of the flow field produced by a quadcopter operating in axial descent by means of Particle Image Velocimetry (PIV). PIV was used to investigate the flow for a range of quadcopter rotor configurations and descent velocity ratios and results were compared with those produced by a tandem rotor. Time-averaged data was used to characterise the general structure of the flow field, whilst the unsteady features of the flow were investigated using a statistical analysis of the velocity fluctuations. It was found that for low enough rotor spacings, the wakes of the four rotors coalesce as a single wake. In this case, when the descent velocity is increased, the quadrotor undergoes one single, global, vortex ring state instead of four separate ones, one per rotor.