Rapid Aerodynamic Method for Interacting Sails

Licentiate thesis, 2023

Rapid performance prediction tools are required for the evaluation, optimization, and comparison of different wind propulsion systems (WPSs). These tools should capture viscous aerodynamic flow effects in 3D, especially the maximum propulsion force, stall angles and interaction effects between the lift-generating units. This thesis presents such a rapid aerodynamic calculation method that combines viscous pre-tabulated data with an inviscid lifting line/potential flow model to account for 3D sail–sail interaction effects.

The proposed method was evaluated in two validation studies; in the first study, validation data was obtained via CFD simulations and in the second via wind tunnel tests. The WPS test case consisted of multiple wingsails.

The results showed that the interaction model improved the prediction considerably compared to when interaction was not accounted for. The interaction affected the generated total driving force and especially the moment, which was well predicted by the method. The angle sweep studies indicated that the method could predict the maximum driving force and the stall angles of the sails with acceptable accuracy. Compared to 3D CFD simulations or wind tunnel testing the computational cost of the method was negligible.

This thesis concludes that the proposed rapid method is a suitable complement to more costly high-fidelity tools. Its ability to predict how the forces and moments change due to sail–sail interaction effects is important because it impacts the overall performance of the ship. Future work will include further validation studies for different WPS configurations, evaluation of possible method improvements and investigations on how to implement of the method in the ship design process.