Author(s): W. Altai; M. Shafie; V. H. Chu
Linked Author(s):
Keywords: Recirculating flow; Turbulent mixing; Coherent structure; Bed-friction effect; Open-channel flow
Abstract: Recirculating flow in a shallow basin was studied experimentally for friction effect on turbulent exchange process. Dye was introduced into the basin during the experiments. Measurements of the dye concentration were made using a video imaging method. The turbulent intensities and the retention times in different regions of the recirculating flow were determined for a range of Froude number Fr = U/ (gh) `1/2 varying from 0.14 to 0.68 and a range of bed-friction number S = c_f L/2h from 0.05 to 0.13. A core of relatively non-turbulent flow was observed to occupy the central region of the basin where the retention time scale was significantly greater than the rest of the basin. In the region outside of the core, the exchange process was governed by the circulation of eddies around the perimeter of the basin. The turbulent structure of the flow in small water depth was more coherent than the flow of greater water depth. However, the dimensionless mass-exchange flow rate was not significantly dependent on the degree of coherency of the turbulent motion.
Year: 2001