Author(s): Deping Cao
Linked Author(s): Deping Cao
Keywords: Seepage effects; Sediment transport; Closed-conduit flow; Suction; Injection
Abstract: Laboratory experiments were conducted to investigate the influence of both suction and injection on sediment transport in closed-conduit flows in this study. The results of experiment tests on suction show that the bed load transport rate essentially remains unchanged for small values of suction rates before abruptly increasing beyond a certain threshold. Theoretical analyses of the forces acting on a spherical particle also are conducted and a conceptual model set up to analyze suction effects on particle mobility by considering the near-bed velocities (see Fig. 1). The model hypothesizes that (1) the bed particle experiences an additional downward vertical drag force induced by suction; and (2) increasing suction will lead to larger horizontal and vertical near-bed velocities, which enhances both the driving force and effective weight of the particle. To qualitatively examine how suction affects the near-bed flow behavior, physical modeling capability software was used to simulate the physical system and the results confirm that the near-bed velocities increase with suction. The results of experiment tests on injection show that the sediment transport rate essentially remains unchanged when the ratio of the injection velocity and that at boiling, Vi/Vcr < 10. However, significant sediment transport rate is observed when Vi/Vcr increases beyond this limit. In the literature, three semi-empirical models have been developed to relate seepage effects on the sediment transport rate. The experimentally measured data in the pre- and post-boiling condition (Liu and Chiew 2014, and the present study, respectively) are compared with these models. The results show that the models of Francalanci et al. (2008) and Nielsen et al. (2001) perform poorly in predicting injection effects on the sediment transport. Although Yang’s (2013) model could reasonably predict the influence of injection on the sediment transport rate in the post-boiling condition, it similarly fails when applied to the pre-boiling condition.
Year: 2023