Aerodynamic efficiency and wake evolution of a rotating cylinder at Re = 1.438 × 106

Flettner rotors are capable of converting wind energy into effective propulsion, offering both economic and environmental benefits for commercial ships. This study investigates the aerodynamic characteristics of a rotating cylinder under supercritical Reynolds number conditions using a numerical simulation approach based on the Magnus effect. The simulations are conducted at a Reynolds number of 1.438 × 106, with rotation ratios ranging from 0 to 16. Results indicate a strong correlation between the aerodynamic forces and the rotation ratio. A critical rotation ratio of α = 2.3 is identified, at which the lift-to-drag ratio reaches its maximum, signifying optimal aerodynamic performance. Furthermore, the evolution of wake vortex structures is analyzed in detail. It is observed that as the rotation ratio increases, the flow separation point shifts downstream, and the wake undergoes five distinct structural transitions. These findings provide a quantitative foundation for the aerodynamic assessment of Flettner rotor sails and offer valuable insight for improving rotor design and enhancing wind energy utilization efficiency. The study holds significant theoretical and practical implications for the development of sustainable wind-assisted propulsion systems.