PIV Investigation of Aerodynamic Flow Interaction between Eppler 61 Wing Sails and a Cargo Ship Deck

The maritime industry is increasingly adopting wind-assisted ship propulsion (WASP) systems to displace fossil fuel dependency, reduce operational fuel consumption, and curtail greenhouse gas emissions in compliance with international environmental mandates. Among these technologies, rigid wing sails offer exceptional potential for enhancing propulsive efficiency due to their high lift-to-drag characteristics. This work presents a comprehensive experimental investigation exploring the aerodynamic flow patterns generated over a simplified mid-sized cargo ship deck equipped with three rigid wing sails arranged in a tandem configuration. Moving beyond traditional marine geometries, the sails are based on the high-performance Eppler 61 aeronautical airfoil, selected for its advantageous characteristics within low Reynolds number regimes. Experimental data were registered through a Particle Image Velocimetry (PIV) system in the T1 low-speed wind tunnel facility at the National Institute for Aerospace Technology (INTA), Spain, using a 1:150 scaled model. Flow diagnostics were performed at a freestream velocity of 15 m/s. The experimental tests evaluated five apparent wind angles (𝛽= 15°, 30°, 45°, 65°, 80° ) under wing-sails angle of attack (𝛼= 0°, 5°, 10°, 15°). The PIV analysis characterized the non-dimensional velocity fields and turbulence intensity contours to capture sail-to-sail aerodynamic interactions. The results confirmed that the array contributes positively to propulsive generation, generating velocity peaks on the suction side of the wing-sails. However, some aerodynamic interferences have been founded, resulting in a velocity peak reduction between 2.1% and 13.3% for the second sail. At the highest angle of attack (𝛼= 15°), flow detachment and stall were captured on the rear part of the first sail's suction side. These experimental data provide essential information for maximizing multi-sail propulsive efficiency and optimizing future sustainable commercial vessels.