Porous Medium Flow and an Overlying Parallel Flow: PIV Interrogation Area and Overlaps, Interfacial Location, and Depth Ratio Effects

This paper presents an experimental work aimed at studying the effects of particle image velocimetry (PIV) interrogation area and overlaps, location of the interface, as well as depth ratios on the flow at the interface between a model porous medium and an overlying free flow. The porous media were modeled using square arrays of circular rods of diameter and porosity 0.88, filling fraction ranging from 0.47 to 0.75, and depth-to-porous medium pore ratio ranging from 5.75 to 13.69. Using a pressure-driven refractive-index matched viscous fluid, the bulk Reynolds number was kept approximately constant at a regime in which inertia was not a factor. PIV measurements were made across various streamwise-transverse planes of the test section. For the present tests, it was observed that PIV interrogation area (IA) and overlap effects on the interfacial velocities are negligible when the IA sizes in dimensionless units ranged from 0.017 to 0.145 in flow parameters and 0.036 to 0.300 in porous media parameters. Other dimensionless slip parameters are however significantly affected. Interfacial slip parameters of porous media models were found to change by as much as 120 % with change in the interfacial location. The interfacial location sensitivity was also found to be dependent on the direction of deviation, the type of porous medium, and depth ratios. Volume averaged results showed that for flows over models of porous media, the depth-to-porous medium pore ratio effects are more prominent compared with the filling fraction effects, for both two- and three-dimensional porous media.