Experimental investigation of vortex ring state for multicopters

Abstract

The vortex ring state (VRS) regime for multicopters has been experimentally investigated within GARTEUR AG28: Vortex Ring State via thrust and power measurements as well as stereo particle image velocimetry, at descent angles between 40◦ and 90◦, and normalised descent rates between -0.4 and -1.7, covering the whole area of flight susceptible to VRS. Two different configurations have been investigated: the isolated rotor, used as a reference testcase, and the quadrotor configuration. The objective of the present study is to investigate the configurational effects on the quadrotor configuration in vortex ring state and the deviation of its performance from existing experimental data for conventional helicopters. Thrust data and stereo-PIV fields show that while both the single rotor and multicopter exhibit qualitative similarities to helicopters in their VRS behaviour, the quadrotor configuration proved more susceptible to VRS: based on mean thrust reduction, the quadrotor configuration showed a broader region of the flight envelope affected by VRS compared to the isolated rotor configuration. However, similar mean thrust reduction levels are obtained for the two configurations, with the highest reduction measured at roughly 30% for every configuration. The velocimetry measurements proved that, for the Quadrotor configuration, a single recirculation region wraps around the device when in vortex ring state, forming a unified vortex ring.