Using the wind as an additional propelling force for modern cargo ships is on the rise. This is due to the regulations about greenhouse gas emissions. Various wind units are available to create a propelling force for the ship. One of these wind units is the suction wing. A couple of ships are equipped with it, like the Amadeus Saffier. Some reasons for choosing a suction wing are the compactness, controllability from the bridge and the ability to create higher lift than traditional sails.
The suction wing in itself has already been researched. Next to that, the optimal position in terms of counteracting its forces with the ship’s hydrodynamic forces is investigated. In the middle of these two lies the gap of the actual forces and interactions between the ship and the suction wing at sea.
This research investigates the interaction effects between the ship, deckhouse and wind units and how they influence the forces. The goal is to get insight into the interaction effects and their consequences.
Based on that, the suction wings can be positioned on the ship with minimal interaction and on fewer disturbed regions. Moreover, knowing the suction wing forces, which are expected to be generated at sea, leads to better estimations of the engine power reduction and savings in emissions. Additionally, this knowledge can be applied to design the ship and suction wings more effectively for use at sea on a wind-assisted vessel. All of this helps to optimise the wind-assisted ships and reduce emissions.
Computational fluid dynamics (CFD) simulations with the RBVMS (residual-based variational multiscale) code were conducted to get insight into the flow. A simple, real-size model of a ship hull, deckhouse and suction wing was created for the CFD simulation. The ship and suction wing were simulated separately, but also in a combined case. Results were obtained for two wind conditions, respectively a uniform wind of 10 m/s and a logarithmic wind profile in an apparent wind angle of 30∘. Reliable results were achieved based on a mesh size study for the individual cases. Additional studies were done for the suction wing to get reliable results. These included a domain size study and the calculation in 2D and 3D. Moreover, a realistic suction pressure and blowing velocity were identified and matched for each wind condition. The lift and drag coefficients were validated with experiments.
The 2D and 3D simulations of the suction wing showed that the 3D case is not an extrapolation of the 2D case. In the 3D simulation, the lift-induced drag plays a strong role, which is produced by the tip vortices.
The interaction effects were investigated with vector plots, the lift and drag coefficient and frequency spectra. The frequency spectra were realised through a polynomial fit of the forces and the Discrete Fourier Transform. The results showed a strong interaction between the ship and the suction wing. Especially close to the ship deck, more turbulence and a change in wind speed can be seen. For the simulated cases, the deckhouse stayed unaffected.
Superposition was investigated to determine if it is possible to have a faster way of knowing the wind above the ship deck at different angles and ship configurations at sea. Linear superposition was applied to the single simulations to compare them with the full simulation. Linear superposition can not represent the full simulation. Nevertheless, it can be used to get a better approximation of the flow behaviour of the full simulation than using only one single simulation.