Particle image velocimetry (PIV) has been used to investigate transitional and turbulent flow in a randomly packed bed of mono-sized transparent spheres at particle Reynolds number, 20 < Re p < 3220. The refractive index of the liquid is matched with the spheres to provide optical access to the flow within the bed without distortions. Integrated pressure drop data yield that Darcy law is valid at Re p ≈ 80. The PIV measurements show that the velocity fluctuations increase and that the time-averaged velocity distribution start to change at lower Re p . The probability for relatively low and high velocities decreases with Re p and recirculation zones that appear in inertia dominated flows are suppressed by the turbulent flow at higher Re p . Hence there is a maximum of recirculation at about Re p ≈ 400. Finally, statistical analysis of the spatial distribution of time-averaged velocities shows that the velocity distribution is clearly and weakly self-similar with respect to Re p for turbulent and laminar flow, respectively.

Stereoscopic particle image velocimetry has been used to investigate inertia dominated, transitional and turbulent flow in a randomly packed bed of monosized PMMA spheres. By using an index-matched fluid, the bed is optically transparent and measurements can be performed in an arbitrary position within the porous bed. The velocity field observations are carried out for particle Reynolds numbers, Re p , between 20 and 3220, and the sampling is done at a frequency of 75 Hz. Results show that, in porous media, the dynamics of the flow can vary significantly from pore to pore. At Re p around 400 the spatially averaged time fluctuations of total velocity reach a maximum and the spatial variation of the time-averaged total velocity, u tot increases up to about the same Re p and then it decreases. Also in the studied planes, a considerable amount of the fluid moves in the perpendicular directions to the main flow direction and the time-averaged magnitude of the velocity in the main direction, u x , has an averaged minimum of 40% of the magnitude of u tot at Re p about 400. For Re p > 1600, this ratio is nearly constant and u x is on average a little bit less than 50% of u tot . The importance of the results for longitudinal and transverse dispersion is discussed.

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The transition from laminar to turbulent flow in porous media is studied with a pore doublet model consisting of pipes with different diameter. The pressure drop over all pipes is recorded by pressure transducers for different flow rates. Results show that the flow in the parallel pipes is redistributed when turbulent slugs pass through one of them and six different flow zones were identified by studying the difference between the Re in the parallel pipes. Each flow zone starts when the flow regime of one of the pipe changes. Transitional flow of each pipe increases the correlation between different pipes pressure drop fluctuations. Frequency analysis of the pressure drops show that the larger pipe makes the system to oscillate by the presence of turbulent patches in its flow. However, when the flow in the smaller pipe enters into the transitional zone the larger pipe starts to follow the fluctuations of the smaller pipe.