Author(s): Dechao Hu; Deyu Zhong; Guangqian Wang; Hongwu Zhang
Linked Author(s): Guangqian Wang
Keywords: Three-dimensional; Numerical model; Free-surface flow; Circulation extraction
Abstract: The circulations (secondary flow) at cross sections are common structures of free-surface flows in natural rivers. They play important roles in shaping the flow regime, governing sediment transport and fluvial processes. The extraction and analysis will help improving the understanding of river mechanics. However, the circulation at an arbitrary cross-section may not be well represented by the cross-sectional flow (transverse velocity field). More over, the irregular, multiple-channel, compound cross-section profiles of natural rivers add difficulties to extract circulations. Based on the 3D velocity field produced by a numerical model on the unstructured, sigma grid, a method for extracting large-scale circulations at arbitrary cross sections of natural rivers is proposed and validated. The local spatial helix structure is first extracted from the 3D velocity field, and then circulations at cross sections are obtained by projection. The new method is validated by using the field data of a natural riverbend “Si-Ma River Bend” in lower Yangtze River. The extracted circulations and their intensities agree well with the field data. Through a further illustration, the new scheme is found to be sophisticated enough to catch multiple, opposite circulations at cross sections, and describe the circulation evolution along the river.
Year: 2013