Microscopic modeling of turbulent flow over and within a porous bed

In this study the characteristics of turbulent flow in an open channel with a porous bed are studied numerically. The Reynolds-Averaged Navier-Stokes equations are solved numerically in conjunction with the low-Reynolds k-epsilon turbulence model of Launder-Sharma above and within the porous bed. The latter is represented by a bundle of cylindrical rods (with the rods' axes being normal to the main flow direction) of certain diameter and spacing resulting in high permeabilities, ranging from 35 to 3300 [mm(2)] and porosities from 0.7 to 0.9. With such an arrangement the microscopic modelling and simulation of flow within and above the porous layer is possible. Main emphasis is given to the effects of relative porous thickness and Darcy number on the flow characteristics over and within the porous bed. Computed velocities indicate the significant influence of the above-mentioned factors on the flow field. Also, computed discharge indicates the capacity of such channels compared to the respective ones with impermeable bed. Computed velocities and turbulence kinetic energy are compared satisfactorily with available experimental measurements taken at the Hydraulics Laboratory of Aristotle University of Thessaloniki.