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PIV measurement of turbulence over a streamwise preferential porous medium

This study examines the possibility of orthotropic porous medium whose streamwise permeability is larger than the wall-normal permeability to reduce turbulent friction inspired by recent numerical studies of Rosti et al. (2018); G´omez-de Segura and Garc´ıa-Mayoral (2019). Because G´omez-de Segura and Garc´ıa-Mayoral (2019) used Brinkman equation to approximate the flow in the porous media, it is uncertain that such porous media really reduce the friction. We make a layered porous medium, which satisfies the drag reducing condition suggested by G´omez-de Segura and Garc´ıa-Mayoral (2019), and carry out particle image velocimetry measurements of turbulent square duct flows over it and examine the drag reduction probability. From the analyses of the obtained data, it is found that the friction on the porous-wall is nearly the same as that of the smooth-wall at Reb < 10000 and tends to increase at Reb > 10000.