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Numerical simulation on drag increasing mechanisms of a flexible vegetation array in a laminar boundary layer flow
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DOI：10.1016/j.jfluidstructs.2026.104596.png)
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Abstract
En 中文
Flexible aquatic vegetation widely exists in nature and because of deformation and swaying, its drag characteristics differ from those of rigid body. In this paper, the drag of a flexible finite-length vegetation array in a two-dimensional laminar boundary layer flow is investigated under different bending rigidity γ and gap distance d through numerical simulations, where the drag of each vegetation element is calculated directly. As per our previous work (Ni et al. (2025a)), a finite-length flexible vegetation array can be divided into distinct zones where the large-scale vortices are in developing (D), transition (T), dissipation (D*), and interaction (I). The drag features of the above four dynamic zones are explored, and the drag under the stable shear layer upstream the dynamic zones is also analyzed. In addition, the variation of the whole array drag with γ and d is discussed and the contribution of drag in each zone is elucidated. The results indicate that the flow adjustment at the leading edge of the array is the immediate cause of different drag features in the static zone, which can be further classified into zones P (positive drag), N (negative drag), and Z (almost zero drag). The drag in zone P is redistributed to all elements in this zone, and the negative drag in zone N originates from the low-pressure center appearing simultaneously with the high flow velocity. In zones D and T, two mechanisms leading to drag increasing compared with a rigid counterpart are revealed. One mainly occurs when the Kelvin–Helmholtz (KH) vortex passes by the element, and the increased drag results from the rapid swaying of the element owing to the attraction of low pressure. The other appears when γ is small, as a more closed high-pressure center is formed inside the array between the two adjacent KH vortices. No drag increasing effect is found in zone D*, while the drag features in zone I follow those of its upstream zone. The drag in zones D and T contributes up to 50% of the whole drag of the array, and the effects of γ and d on the whole drag are achieved by changing the number of vegetation elements contained in each zone.
Keywords:
Flexible vegetation
Drag mechanisms
Laminar boundary layer
Vortex dynamics
Bending rigidity
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