Experimental studies of wind and aerodynamics for wind-powered commercial ships

QC240909

Abstract

The wind is emerging again as a viable source of energy to propel commercial ships. This renewal is partially driven by new regulations aiming at cutting down the greenhouse gas emissions from the shipping industry, and partially by some actors who are willing to take a step towards this paradigm shift. Many different technological solutions have been developed or are under development since the past few years, some aiming at assisting the engines with extra wind energy and others aiming at vessels fully wind-powered. 

Although sailing has existed since a long time, transitioning from a tall ship or a leisure yacht to a sailing commercial vessel is complex. Some aspects of the physics of sailing are not fully understood yet, at least not when applied to ships that are so different from existing sailing ships. Large cargo vessels will require several sails or wings, to ensure enough propulsive force. The interaction effects between lifting surfaces placed so close to each other are only partially understood, and have only been little studied when it comes to arrays of wings. The impact of the hull on the flow is something rarely studied, partly because conventional sailing boats do not have such large hulls, and partly because it only matters for fast racing yachts. The interaction effects, both wing-wing and wing-hull are studied in this thesis with different methods: a potential flow numerical code, wind tunnel experiments and with a free-sailing 7 meter long model equipped with different types of sensors. 

Another question arises from the heights that wind propulsion devices reach above sea level, which are higher than any existing sailing boat, with the exception of few leisure super-yachts. The wind at these heights is partially unknown, at least offshore where ships operate. Both the evolution of wind with height and its unsteadiness have rarely been measured at heights relevant for wind propulsion. This thesis presents unique wind measurements of the Atmospheric Boundary Layer over the North-Atlantic Ocean, performed from a commercial ship in operation with a wind lidar, in an attempt to provide better knowledge of the wind conditions at sea.  

In order to ensure that sailing ships will be operated in an efficient and safe manner, automation systems and control algorithms need to be developed, both for the wings and the whole vessel. These control systems will need to be able to account for all interaction effects and the unsteadiness of the wind. This thesis presents results from tests performed at sea, in real conditions, on a 7 m long scale model wind-powered car carrier, and highlights the effects of unsteadiness. The results presented in this thesis pave the way towards the development of these efficient control systems.

Throughout the thesis, different methods, with varying complexity and fidelity have been used. The results and the discussions presented in this thesis showcase the importance of mixing and combining different methods, experimental and numerical, with low and high fidelity, in order to fully understand the new questions raised by the development of sailing cargo vessels.

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