A PIV/PTV experiment on sediment transport in a horizontal open channel flow

In this paper, sediment transport in a turbulent open channel flow is studied using a combined PIV-PTV technique. We introduced 350 mu m polystyrene particles at three different streamwise locations near the free surface in a Re= 10, 000 flow. It is shown that a distance of the order h < u >/v(rms) is needed for the sediment profile to become completely developed. At smaller distances, gradient diffusion modeling cannot be applied. In this situation, the downward transport of sediment is governed by sweeps with a vertical scale of the order of the water depth, whereas ejections are the main contributor to the upward flux of sediment in the fully developed situation. Because of this, the particle streamwise velocity is higher than the fluid velocity when the particles are still adapting, but lower than the fluid velocity in the fully developed situation. Some examples of instantaneous flow structures transporting the particles are shown.