Influence of Darcy and Reynolds numbers on flow past a porous circular cylinder

This study employs a unified one-domain immersed boundary method to explore the wake behavior of flow past a porous circular cylinder across a broad span of Darcy (Da) and Reynolds (Re) numbers. A detailed mode diagram identifies four wake regimes: steady flow, recirculation without shedding, classical vortex shedding with recirculation, and a previously unreported far-wake shedding mode lacking a recirculation bubble. The interaction between Da and Re is examined: increasing Re extends the shear layer, promoting instability and vortex shedding, while also enhancing through-flow, which stabilizes the wake and attenuates drag and lift oscillations. In contrast, increasing Da reduces flow resistance, strengthens bleed-through, delays separation, shortens the recirculation zone, alters the separation angle, and induces a nonlinear drag response with significant lift suppression. Pressure fields and force analyses clarify the underlying mechanisms of each transition. The results advance the understanding of unsteady flows around porous bluff bodies and inform strategies for drag management and flow control in engineering systems.