Structure of turbulence over non uniform sand bed channel with downward seepage

Experimental investigations were carried out to investigate turbulent flow characteristics in non-uniform sand bed channels for both no seepage and seepage flow. Steady flows over non-uniform sand bed channel were simulated experimentally with downward seepage applied through the boundary. Measures of turbulent parameters such as velocity, Reynolds shear stresses, thickness of roughness sub layer and shear velocities were found increasing with seepage. The turbulent diffusivity and mixing length decrease in presence of seepage. The quadrant analysis suggests that the relative contributions of bursting events increased throughout the flow layer and the thickness of the zone of dominance of sweep event increases with seepage which is responsible for increment in bed material transport. The mean time of occurrence of ejections and sweeps in downward seepage are more persistent than those in no seepage. The analysis of third order moments states that an upward downstream flux of turbulent kinetic energy is observed over the near bed surface giving rise to sweeps with seepage. The turbulent kinetic energy fluxes increase in presence of seepage within the near bed flow. The increased in bed load transport with seepage associated with an increase in flow turbulence production corresponds with decrease in turbulent kinetic energy dissipation, pressure energy diffusion and turbulent diffusion. The traversing length decreases and size of eddies increases with seepage.