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Suction Effects on Flow Behavior and Sediment Transport in Closed-Conduit Flows

Author(s): Cao Deping; Chiew Yee-Meng

Linked Author(s): Yee Meng Chiew

Keywords: Suction; Sediment transport; Flow behavior; Closed-conduit flow

Abstract: Many studies have been carried out to investigate suction effects on flow behaviour and sediment transport. Published literature has shown that suction has a significant impact on bed erosion and deposition in a fluvial system. In the present study, experiments are conducted to investigate suction effects on sediment transport in a 9 m long closed conduit with a 50-cm long zone that is subjected to uniform suction. Cohesionless sediment particles with medium diameter = 0. 80 mm were used in the study. A 50-cm long sediment recess with a sand trap is constructed to collect the sand transported from the suction zone in the experiments, allowing the amount of sand transported to be measured directly. The results show that an increase in suction rate leads to an increase in bedload transport rate. The results are consistent with some published results of suction effects on sediment transport in open channel flow. A possible explanation is proposed to account for the reason of increasing qb with increasing suction rate. Increasing suction rate leads to both increasing horizontal velocity ub and vertical velocity vb at the bed level. It is, therefore, surmised that increasing ub will increase the drag force, causing the sediment particles to move more easily or faster while increasing vb will increase the frictional force between particles, thus decelerate sediment transport rate. To verify this explanation, the Particle Image Velocimetry (PIV) was used to measure the flow behavior with different suction rates in this study. The experimental measurement shows that both the horizontal and vertical approach velocities increase with increasing suction rates. Suction effects on turbulence characteristics are also investigated; the data show that turbulence increases with increasing suction rate when suction rate is within a certain range and decreases beyond that range.


Year: 2013

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