Inertial Effects on Fluid Flow Through Natural Porous Media

We investigated the nonlinear effects of gravity‐driven fluid flow through a two‐dimensional, moderately low‐porosity, packed bed of stubby stone grains in Darcy, and post Darcy regimes. We focused on preferential channel formation, tortuosity, spatial distribution of kinetic energy, and vortex formation. We show that nonlinear effects dominate at relatively high Reynolds numbers, even though the deviation from Darcy's law is not visible in friction factor measurements. A backward‐flow fraction captures the earliest formation and growth of recirculation zones; the participation number increases monotonically, indicating a progressive delocalization of kinetic energy; and tortuosity exhibits a non‐monotonous trend—initially flat/slightly decreasing, then rising in the inertial regime. The apparent permeability decreases with . These results explain why friction‐factor‐only indicator can obscure the onset of inertial effects in the real porous rocks with moderate porosity, lower than of those studied previously and identify as an early, robust indicator of recirculation. We further notice an increased asymmetry of the flow field revealed by vorticity analysis and surprising correlation between tortuosity and apparent permeability in the inertial flow regime, where the relation holds.