See more from this Session: Connections - the Role of Connectivity In Soil Processes: I
In this presentation, we will show that the instability is a direct consequence of pore scale processes where the contact angle becomes less concave under transient conditions at the wetting front than under static conductions. This phenomenon is known under the general name of dynamic contact angle. Many contradicting theories have been proposed for explaining the dynamic contact angle. In this presentation we will show that by solving the fluid flow equations at the pore scale with the incompressible Navier-Stokes’ equation, the dynamic contact angle is a function of the velocity of the wetting front (and thus the pressure applied) and to lesser degree by the static contact angle as long as it exceeds the pressure needed for water to enter the pore. Our results compare well with the experimental observations of Hoffman in the seventies in which the change in contact angle was measured as a function of flow velocity.