Investigation of bottom boundary layer dynamics of movable bed by using enhanced PIV technique

The behavior of the bottom boundary layer of a natural rippled bed and plane bed is investigated utilizing PIV technique. An enhanced approach of the PIV is developed on the basis of the Minimum Quadratic Difference, (MQD), which is better compared with the conventional cross-correlation method. Information of pixels below the instantaneous unmoved level is expelled from the calculation process so that the velocity close to the bed is computed accurately. The flow field over the natural rippled bed is measured with the enhanced approach and comparison with the LDV measurements showed that the measurements of flow field by the enhanced PIV axe in a good agreement with the LDV measurements. Having verified the technique, the technique is utilized to measure the net volume flux of sand transported in sheetflow under asymmetric oscillation. The net mass transport is measured to be compared with the PIV measurement. The sand concentration is estimated from brightness through a calibration relationship. The velocity is measured and then the volume flux is integrated. It was found that the technique predicted net onshore transport although it slightly underestimated the volume flux.