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The paper reports an experimental investigation of flow through model porous medium adjacent to open flow in a two-dimensional channel. The model consists of circular cylindrical rods installed vertically on the bottom wall of the channel in regular square arrays. The channel height was kept constant but the ratio of rod height to channel height was varied to simulate different filling fractions. Various combinations of rod diameter and rod spacing were chosen to achieve solid volume fractions (ϕ) in the range 0.01⩽ϕ⩽0.50. A viscous fluid having a refractive index similar to that of the rods was selected as the working fluid. Particle image velocimetry was used to conduct detailed velocity measurements between the rods and in the open flow between the top edges of the rods and the top wall of the channel. From these measurements, values of the slip velocity at the interface between the rods and the open flow were determined. It was found that values of the slip velocity normalized by the maximum velocity in the open flow depend on solid volume fraction, rod spacing, and fraction of channel filled by rods. The slip velocity made dimensionless by the shear rate at the interface were higher for the larger filling fraction but independent of solid volume fraction and rod spacing.

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