Aerodynamic performance of a rotating cylinder at <i>Re</i> = 8.215 × 105

This study investigates the aerodynamic characteristics of a rotating cylinder under critical Reynolds number condition, aiming to establish a theoretical basis for the optimization of rotary sails and the enhancement of ship-assisted propulsion systems. By improving aerodynamic efficiency, this research contributes to economic benefits and environmental sustainability. Based on the Magnus effect, numerical simulations were conducted using Fluent to analyze the flow around a rotating cylinder at a Reynolds number of Re = 8.215 × 105. The study explores a wide range of rotational ratios from 0 to 16 to compare the wake dynamics and fluid force characteristics under varying conditions. The results demonstrate a clear relationship between the rotational ratio and aerodynamic performance. Specifically, the lift and drag coefficients exhibit distinct trends as the rotational ratio increases, with a critical rotational ratio of 2.5 identified as yielding optimal aerodynamic efficiency. At this rotational ratio, the lift-to-drag ratio reaches its maximum, marking the cylinder's best performance under the studied conditions. Furthermore, the investigation reveals significant changes in the wake structure and separation point position. As the rotational ratio increases, the separation point gradually moves downstream, with its position ranging from 82° to 93° relative to the stagnation point. The wake vortex structure undergoes five distinct developmental regimes, illustrating progressive changes in flow behavior that are closely linked to the rotational ratio.