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Effects of emergent and submerged rigid vegetation configurations on gravity current dynamics

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Abstract

The propagation and hydrodynamic processes of lock-exchange gravity current through vegetation regions were investigated experimentally. Experimental results show that the presence of vegetation can prominently advance the transition position of the gravity current from the slumping phase to the self-similar phase. The process of two-heads propagation can be divided into three stages: the coordinated advance stage (vegetation height controls), the overtaking stage (entrainment process and vegetation friction dominate), and the merge stage (vegetation density controls). After an adjustment period, the bulk slope angle \(\beta_b\) of the triangular gravity current converges to a constant terminal value. A modified empirical equation is fitted to better meet the stable convergence of the terminal bulk slope angle \(\beta_b\). The mixing layer formed at the transverse boundary between the vegetation and no-vegetation part can promote fluid entrainment. For the submerged vegetation, the gravity current flows over a new “wall boundary”, i.e. the top of the vegetation region, and causes the negative vorticity. The changes in the vorticity field indicate the presence of vegetation can significantly affect the internal flow-field structure of gravity currents.

Article Highlights

  1. (1)

    The process of two-heads propagation for gravity current flowing within submerged vegetation can be divided into three stages: the coordinated advance stage (vegetation height controls), the overtaking stage (entrainment process and vegetation friction dominate), and the merge stage (vegetation density controls).

  2. (2)

    A modified empirical equation is fitted to better meet the stable convergence of the terminal slope angle \(\beta_b\) for lock-exchange gravity current within vegetation.

  3. (3)

    The vegetation exerts resistance on the gravity current and suppresses the K-H instability at the interface, which weakens the entrainment process, but the mixing layer formed at the transverse boundary of the vegetation region promotes fluid entrainment.

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Acknowledgements

This work was supported by National Key Research and Development Project of China [grant number 2017YFC0405205], Natural Science Foundation of Zhejiang Province of China [grant number LY20A020009], and Fundamental Research Funds for the Central Universities [grant number 2020QNA4038]. The author thanks the laboratory instrument of Ocean College of Zhejiang University for support.

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  1. Ocean College, Zhejiang University, Hangzhou, 316021, Zhejiang Province, China

    Dongrui Han, Jie Xiong, Xiaoyun Xie & Yingtien Lin

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  1. Dongrui Han
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Han, D., Xiong, J., Xie, X. et al. Effects of emergent and submerged rigid vegetation configurations on gravity current dynamics. Environ Fluid Mech 21, 1165–1187 (2021). https://doi.org/10.1007/s10652-021-09814-5

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