Comparison of turbulent flow over solid and porous structures mounted on the bottom of a rectangular channel

Abstract

This paper presents the findings of an experimental study on the turbulent flow field in the vicinity of structures mounted on the bottom of a rectangular open channel. Three model structures used in this study have geometric porosities ( ε ) of 0%, 34.9% and 47.5%. Detailed measurements of the time-averaged velocity components, turbulent intensity components, turbulent kinetic energy and Reynolds stress were taken by the acoustic Doppler velocimeter (ADV) at different locations around the structures. Measurements obtained with the electro-magnetic micro-velocimeter were used to observe the velocity distributions within the porous structures. As the structure porosity increases, the turbulence intensity, turbulent kinetic energy and Reynolds shear stress over the structure all decrease. Among the structures used in this study, the porous structures show the elongating of the recirculation region in the downstream direction due to bleed flow passing through the gaps of the structures. Significant maximum streamwise turbulent intensity of the porous structure with ε = 47.5 % decreases by about 37% compared to that of the solid structure ( ε = 0 % ). The data presented in this paper would be useful to develop and verify mathematical models for flow both over and within a porous structure.