Experiments on the wake flow behind different configurations of multirotor wind turbines

Abstract

Multirotor wind turbine concepts have recently emerged as a promising alternative to conventional turbines. When arranged in farms, the wake flow behind multirotor assemblies becomes an important factor in the cost-of-energy equation. This paper presents a lab-scale experiment on the effect of rotor number, inter-rotor spacing and yaw-misalignment on the wake development behind a simplified multirotor model. The flow characteristics are investigated by towing different arrangements of porous discs in a large water tank while traversing an Acoustic Doppler Velocimeter in the wake. Results show lower initial velocity deficits in a multirotor’s near wake, whereas its far wake is observed to be similar to the one of a single rotor. The wake’s recovery rate is first stimulated by additional shear stresses in between the single rotors, while flattening off further downstream. Measurements on the wake flow behind individual yaw on the single rotors compared to collective yaw on all rotors show a similar deflection of the mean velocity deficit in the wake.