Capillary Action (wicking): Water Flows in a Porous Media

Capillary Action (Wicking), Water Flows in Porous Media, ANSYS Fluent Simulation Training

Description

This project simulates water flow in porous media driven by capillary action using ANSYS Fluent. Capillary action is the process by which a liquid moves through a narrow space without external assistance — and sometimes even against opposing forces like gravity — a phenomenon relevant to plant vessel transport, wicking materials, and various porous flow applications.

The 3D geometry was designed in Design Modeler, consisting of three sections: a lower region containing resident water, an upper region containing resident air, and a middle vertical pipe defined as a porous zone connecting the two. The domain was meshed in ANSYS Meshing, totaling 178,325 elements.

Methodology

This simulation models simple porous and capillary flow behavior through a vertical, plant-vessel-like pipe. The porous media model is broadly applicable across single-phase and multiphase problems, including flow through packed beds, filter papers, perforated plates, flow distributors, and tube banks — in each case, incorporating an empirically determined flow resistance within a designated "porous" cell zone, functioning essentially as an added momentum sink within the governing momentum equations.

The Eulerian multiphase model was used to represent the air and water phases, applying the Brooks-Corey model to capture capillary pressure-saturation behavior within the porous zone. Gravitational effects were included at -9.81 m/s² along the y-axis.

Conclusion

Results include 3D velocity fields, air and water volume fraction contours, and simulation animation. The results confirm the expected capillary behavior: resident water begins rising upward through the vessel toward its top, driven purely by the capillary effect within the porous zone — despite acting against gravity, illustrating the core physical mechanism this simulation set out to capture.