While the awareness of global warming rises, transport over sea remains a large contributor to green house gas emissions. New regulations imposed by the International Maritime Organization (IMO) aim to reduce the emission of green house gasses. Consequently, ship owners turn to technological solutions in order to achieve this. The Ventifoil from Econowind is a promising device in the field of Wind Assisted Ship Propulsion (WASP). By applying boundary layer suction, this airfoil shaped profile can generate large aerodynamic forces, which are
used as additional propulsion to reduce fuel consumption. Often multiple devices are installed on the deck of a vessel.

Literature shows that the aerodynamic interaction between multiple airfoils can significantly influence the local flow conditions in which each individual device operates. Nonetheless, literature agrees that it is possible to mitigate detrimental effects by adapting to the local conditions. The operational guideline of the Ventifoils are based on the far-field wind conditions. Consequently, aerodynamic interaction between Ventifoils is not considered. This leads to the main research question: "To what extend does aerodynamic interaction between two Ventifoils mutually affect aerodynamic performance?". This thesis aims to analyse aerodynamic interaction using a numerical Lifting Line Model (LLM). This method has the potential of evaluating a broad range of operational and environmental conditions in limited computational time.

Aerodynamic interaction between two Ventifoils will be evaluated over a range of apparent wind angles between 0◦ and 180◦, for two different absolute distances. The results fromthe LLM will be validated by means of three dimensional, steady Reynolds Averaged Navier Stokes (RANS) simulations. Five different interaction components will be analysed, being; changes in flow angle, changes in flow velocity, viscous interaction, pressure field interaction,
and boundary layer suction interaction.

The results reveal that aerodynamic interaction can reduce the lift and drag coefficients by multiple tens of percentages. It is found that the reduction ratio of the thrust force coefficient, CX, varies between −16% and −1% relative to a single isolated Ventifoil. The magnitude is mainly depending on the relative position of the devices. It is concluded that the interaction is most significant if the devices are positioned closely near each other and parallel to the flow
direction. Both methods show good qualitative agreement. It is concluded that discrepancies in the magnitude of reduction ratios can be attributed to modelling differences in terms of viscosity, pressure fields and boundary layer suction. Better quantitative agreement is found for larger absolute distances. The LLM is furthermore used to maximize CX by optimizing the angle of attack of each Ventifoil independently. The resulting increase in CX showed to be between +5% and +11% added to the non-optimized reduction ratio.