The effects of the aerodynamic interaction on the performance of two Flettner rotors

Flettner rotors are nowadays becoming a widespread solution for wind-assisted propulsion. To increase the fuel savings of the ship on which they are installed, multiple devices are typically used. However, in the performance estimate of these hybrid ships, it is currently assumed that Flettner rotors operate independently, regardless of the number of devices employed and their relative position on the ship's deck. The present investigation deals with a wind-tunnel experimental campaign aimed at understanding the aerodynamic interaction effects on the performance of two similar Flettner rotors. The study indicates that the aerodynamic performance of the two Flettner rotors is affected by their interaction, and, generally, this is most noticeable when the devices are set closer to each other and when they are aligned with the wind direction. It is demonstrated that, depending on the apparent wind direction, the layout of the Flettner rotors on the ship's deck has a remarked influence on the driving and heeling force coefficients of the entire rig. Lastly, the velocity ratio is found to play a key role in the determination of how the interaction affects the Flettner rotor aerodynamic performance.