This study examines experimentally the hydrodynamic interaction between a regular porous medium and an adjacent free-flow channel at low Reynolds numbers (Re < 1). The porous medium consists of evenly spaced micro-structured rectangular pillars arranged in a uniform pattern, while the free-flow channel features a rectangular cross-sectional area. The overall arrangement comprises a polydimethylsiloxane microfluidic model where distilled water, doped with fluorescent particles, is the examined fluid. Using micro-particle image velocimetry, single-phase quantitative velocity measurements are carried out at the pore scale to reveal the microscopic characteristics of the flow for such a coupled system. Interfacial velocity-slip and stress-jump coefficients are also evaluated with a volume-averaging method based on the Beavers-Joseph and Ochoa-Tapia-Whitaker models, respectively. The results show that, from a microscopic point of view, parallel flow at the interface is not obtained due to the periodically generated U-shaped flow profile between the interface pillars. However, the interface coefficients show no sensitivity to moderate flow angles. The highly resolved experimental information obtained in this study can also be used for the validation of numerical models providing a unique dataset for free-flow and porous media coupled systems.

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