Flow Structure Identification in Unsteady Flow in Porous Media

This study is an experimental investigation of the turbulent flow structure in randomly packed porous bed made with uniform sized spheres. Results are based on time resolved, two component PIV measurements in individual pore spaces of the bed. Data are presented for pore Reynolds number range of 54–3964. Three different flow regimes are identified, steady laminar, and unsteady transitional and turbulent flows. Small scale coherent vortical structures are visualized, by performing large eddy scale decomposition, for pore Reynolds number of greater than 1000. Quantative analysis of vortical coherent structures was performed using swirl strength analysis. The number density of vortical structures is found to monotonically increase gradually with pore Reynolds number. The rotation rate of these vortical structures is found to increase linearly with pore Reynolds number. The stretching rate (linear deformation) of the eddies were calculated using continuity to determine the out of plane stretching. The ratio of stretching rate to swirl strength (rotation rate) shows a normal distribution which collapsed onto a single curve. The convective velocities of the structures show a symmetric distribution with a peak value close to 0.8 times the average pore velocity.