Flow‐Dependent Inertial Permeability Defines Crossover Between Darcy and Forchheimer Flow Regimes

We present mechanistic evidence that the Forchheimer inertial permeability coefficient () is flow‐dependent in the weak‐to‐intermediate inertia crossover regime, governed by pore‐scale eddy growth‐to‐confinement dynamics. In contrast to classical theory, attains steady‐state () asymptotically in the dominant inertial regime, marking the validity of Forchheimer law. This highlights a hydrodynamic gap between Darcy and Forchheimer regimes, which is addressed using a physics‐based Eddy‐Growth Dynamics–Inertial Permeability (EG‐DIP) model. The EG‐DIP model contributes to ongoing discussions on inertial permeability by providing a framework to determine , integrate it into Forchheimer law, and suggest a physical basis for estimating . This supports predictive modeling of flow across regimes and identifies as the characteristic medium‐specific property for reliable correlation with porosity, permeability, and grain size. By unifying inertial flow theory through eddy growth dynamics, the EG‐DIP model has direct implications for injection‐induced seismicity, CO 2 storage security, and geothermal energy recovery.