Experimental study on the slip velocity of turbulent flow over and within porous media

Abstract

The phenomenon of coupled flow between free flow and porous media is characteristic of fluid flowing across porous media, but the slip characteristics at the coupling interface need to be further studied. The purpose of this work is to investigate the velocity distribution of turbulence with a high Reynolds number above and in porous media. In this paper, a visual flume test bench is built to simulate porous media as an accumulation of spherical glass beads with a diameter of 10 mm. The free flow velocity of fluid crossing the porous media and the velocity inside the porous media are measured by ultrasonic Doppler velocimetry. The effects of Reynolds number, relative water depth, and porosity parameters on the slip velocity and momentum transfer near the interface are studied. The results show that the slip coefficient of a porous-media bed with 0.331 porosity ranges from 0.000 082 to 0.000 594, while that of a porous-media bed with 0.476 porosity ranges from 0.000 034 to 0.001 068. The slip velocity increases with the increase in Reynolds number but decreases with the increase in relative water depth and porosity. The thickness of the transition layer in the porous-media region is insensitive to the Reynolds number and relative depth, but sensitive to porosity and increases with the increase in porosity. In this study, the influence of effective parameters on turbulent velocity is studied by experiments, which provides an important reference value for the development of a theoretical model in turbulent flow.