Abstract
In natural rivers, patches of vegetation generally expand over their steady wake region in the streamwise direction, forming elongated patches with length (L) greater than their width (b). This paper studies how the wake flows and the vortices develop as the emergent patches expand their length in the streamwise direction. The patches are modeled with the same width but different lengths in laboratory experiments. Behind the patches, the steady wake region (Lw) is not related to the width-related flow blockage (Cdab), where Cd is the drag coefficient, a is the vegetation density. Instead, Lw is related to the length-related flow blockage (CdaL). On this basis, a model is proposed for predicting Lw, which is in good agreement with the measurements. As a patch becomes denser and/or longer (as CdaL increases), the steady wake region becomes shorter (Lw decreases), and vortices are observed closer to the patch trailing edge, producing a turbulence of a greater magnitude beyond Lw. When the flow blockage increases to the limit (CdaL>8), the Karman vortices are observed directly behind the porous patches. These results can be used to explain the longitudinal elongation of the vegetation patches in the field.
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Acknowledgments
This work was supported by the Sichuan Science and Technology Program (Grant No. 2021YFH0028), the China Scholarship Council (Grant No. 202006240062).
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Projects supported by the National Natural Science Foundation of China (52022063, 52179074 and U2040219).
Biography
Zi-jian Yu (1996-), Male, Ph. D. Candidate
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Yu, Zj., Shan, Yq., Liu, C. et al. Wake flow and vortex structures behind emergent vegetation patches elongated in the longitudinal direction. J Hydrodyn 33, 1148–1161 (2021). https://doi.org/10.1007/s42241-022-0112-6
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DOI: https://doi.org/10.1007/s42241-022-0112-6