Methodological Proposal for the Selection and Analysis of the Performance of Rigid Sails Considering Pre-stall and Post-stall Aerodynamic Conditions

The shipping industry is increasingly considering the issues of "green shipping" and "zero-emission shipping", which are closely related to reducing the consumption of fossil fuels to mitigate its environmental impact. In this way, the use of renewable energies is increasingly perceived as part of the energy mix, with the use of rigid sails (wind energy) being one of the tested alternatives as auxiliary propulsion systems. This work studied the fluid-mechanical optimization of the airfoil that defines the cross section geometry of the rigid sail. A methodology was developed to obtain the aerodynamic coefficients of the rigid sail for any position of the sail with respect to the wind depending on the tested airfoil. Once the aerodynamic coefficients were modeled for several angles of attack, the thrust and overturning components generated by the sail force on the boat were computed from before and after airfoil stalling predictive models of the aerodynamic coefficients. From the obtained results, the following two main conclusions can be stated. i) The use of the sail in post-stall conditions for higher angles of incidence (from approximately 90°) substantially improved the thrust generated on the boat. For the case of small incidence angles, it is recommended to set the sail at an angle of attack less than the airfoil stall. ii) Within the symmetrical four-digit NACA series, the symmetrical NACA 0015 airfoil turned out to be the best choice for geometrically defining the rigid sail cross section, as it provided the highest possible thrust while minimizing the overturning force. Key Words: rigid sails, wind powered, airfoil, aerodynamic coefficients, CFD