Fluid Inertia in Laminar Porous Media Flows: A Critical Driver of Mixing and Reaction

Mixing and reaction in porous and fractured media are widely assumed to occur under slow, viscosity-dominated conditions where fluid inertia is negligible and pore-scale transport is limited by diffusion. I will show that this assumption breaks down even at weak inertial levels, well before any transition to turbulence. Even under laminar conditions, weak inertia triggers 3D vortices, braided streamline paths, and symmetry-breaking topologies that eliminate transport barriers and produce global chaotic advection. These flow structures lead to non-monotonic mixing behavior, dramatic increases in transverse dispersion, and localized reaction and mineral precipitation hotspots that reshape permeability from the pore to network scale. Together, these results establish weak fluid inertia as a governing and tunable control parameter for mixing and reaction in porous media—revealing new pathways for manipulating reactive transport in geologic and engineered systems.