Aerodynamic characteristics and drag reduction mechanisms of cylindrical flow controlled by perforated shrouds

Flow control of cylindrical structures is of significant importance in transportation and aviation, where aerodynamic loading and wake instability directly affect structural safety and aerodynamic performance. The present study aims to elucidate the flow-regime transition mechanisms and aerodynamic response characteristics of a smooth circular cylinder enclosed by perforated shrouds with varying porosities at a Reynolds number of Re = 1.4 × 105. Large-eddy simulation is employed to resolve the unsteady turbulent wake dynamics. The physical configuration consists of a smooth cylinder surrounded by concentric perforated shrouds, and the influence of porosity on wake evolution, force characteristics, and nonlinear aerodynamic behavior is systematically investigated. Results reveal that the perforated shroud induces a transition of the classical cylinder wake from an interference-dominated regime to a through-flow coupling regime. At a critical porosity of approximately 12%, a balance between these two regimes is achieved, corresponding to a drag-transition state. Notably, the lift–drag phase relationship undergoes a reversal, with the phase lag angle shifting from 114° to −118°, indicating a fundamental change in vortex–force interaction mechanisms. Phase-space analysis demonstrates that the aerodynamic trajectories evolve from a triangular to a trapezoidal and eventually to a circular distribution with increasing porosity, reflecting progressively stabilized aerodynamic behavior. These findings provide new insights into the nonlinear wake dynamics and drag-modulation mechanisms of perforated shroud-controlled cylinder flows.