A Primer on Inertial Flows in Porous Media

The influence of the inertia on the behavior of flow in porous media has been studied for more than 60 years, particularly within the chemical engineering community where high Reynolds number flows within porous materials are not uncommon. Because in hydrology the focus has been conventionally on the low-Reynolds number (“creeping”) flow regimes, there has been some confusion in hydrology as to the importance and impact of inertial effects on flow in porous media. In particular, the term turbulence has been frequently invoked when discussing inertial flows in porous media, when, in most practical instances, true turbulence is not present. In this presentation, a discussion of the flow regimes possible in porous media flows will be discussed, and some examples of how the inertial component influences the microscale flow dynamics in porous media will be provided. A connection between the microscale inertial regimes and the macroscale constitutive law (i.e., Darcy’s law and its extensions) will be discussed. One important facet of this discussion will be the regime where the Reynolds number is greater than 1, but the flow is still laminar. In these cases the the macroscopic model deviates from Darcy’s law, indicating that laminar flow at the microscale does not necessarily imply that the flow at the macroscale is Darcian.