Fluid–structure interaction in a flexible vegetation canopy in an open channel

Abstract

Submerged flexible vegetation occupies the core of aquatic ecosystem research. Hydrodynamics of submerged flexible vegetation and its interaction with the flow in an open channel are of great significance in studying the mass and momentum transports in the flow. In this study, a numerical model for highly flexible vegetation based on large eddy simulation and the immersed boundary method was used to simulate the flow–vegetation interaction. It is recognised that alternate vortices with opposite sense rotations appear at the flow–vegetation interface. These vortices prompt the vegetation canopy to have wave-like coherent waving motion, commonly called the monami phenomena. The spatial scale and the spreading velocity in the streamwise direction of these vortices determine the wavelength, frequency and amplitude of the vegetation coherent waving motion. In this study, the fast Fourier transform method was applied to analyse the factors affecting the characteristics of the vegetation coherent waving motion. It is revealed that, as the flow velocity increases, the wavelength of the coherent waving motion decreases, while the frequency and amplitude increase. Besides, as the vegetation spacing increases, the wavelength and amplitude of the coherent waving motion increase, but the frequency decreases. Furthermore, an increase in the relative density of vegetation magnifies the amplitude of coherent waving motion without affecting the wavelength and frequency.

Effects of Submerged Flexible Vegetation on Scalar Transport in an Open‐Channel Flow

“…The selection of vegetation area length is based on the earlier study of Wang et al. (2022a, 2022b) on the wavelength of vegetation coherent waving motion. According to Wang et al.…”

“…The selection of vegetation area length is based on the earlier study of Wang et al (2022aWang et al ( , 2022b on the wavelength of vegetation coherent waving motion. According to Wang et al (2022aWang et al ( , 2022b, under the conditions of the flow and vegetation distribution mode set in this study, the wavelength of coherent waving motion of vegetation is about L w = 4.9 hr. Therefore, in order to ensure that the cyclic boundary does not destroy the Kelvin-Helmholtz (KH) vortices structure, two whole wavelengths are selected as the length of vegetation area, which satisfies dx = 2L w = 10 hr.…”

“…Values of Parameters in the Scalar Transport Governing Equation of the lth IBM unit and the (l + 1)-th IBM unit below it (Figure 2). Details of the force analysis of the vegetation are available in Wang et al (2022aWang et al ( , 2022b.…”

Collective dynamics of dense hairy surfaces in turbulent flow

“…It is also important to highlight the technical challenges for experimental investigations, in particular, for measuring the spatial conformation of the fluid flow in the intra-canopy region 5 , as well as isolating the effect of the various governing parameters (e.g., Cauchy and Reynolds number, solid-to-fluid density ratio, reduced velocity). Both issues, on the other hand, can be overcome by the support of computational studies based on direct or large-eddy numerical simulations [23][24][25][26] , with more recent advancements based on fully-resolved approaches where the stems/elements of the canopy are resolved individually and not modelled, e.g., as a continuous porous medium 4,6,11,[27][28][29] .In this work, we aim at deciphering the highlighted issues by means of a high-fidelity computational approach to accurately and comprehensively access both the flow physics and canopy collective dynamics, as well as the motion of the individual stems. Overall, we aim at establishing whether the fluid and structural dynamics act competitively or not, and which of the two has a dominant role.…”

“…It is also important to highlight the technical challenges for experimental investigations, in particular, for measuring the spatial conformation of the fluid flow in the intra-canopy region 5 , as well as isolating the effect of the various governing parameters (e.g., Cauchy and Reynolds number, solid-to-fluid density ratio, reduced velocity). Both issues, on the other hand, can be overcome by the support of computational studies based on direct or large-eddy numerical simulations [23][24][25][26] , with more recent advancements based on fully-resolved approaches where the stems/elements of the canopy are resolved individually and not modelled, e.g., as a continuous porous medium 4,6,11,[27][28][29] .…”