Numerical investigation of the dynamics of flexible vegetations in turbulent open-channel flows

• Published in: Journal of hydrodynamics. Series B 2022-08, Vol.34 (4), p.681-699
• Main Authors: Xu, Dong, Liu, Jia-ning, Wu, Yun-feng, Ji, Chun-ning
• Format: Article
• Language: English
• Subjects: Engineering; Engineering Fluid Dynamics; Hydrology/Water Resources; Numerical and Computational Physics; Simulation
• ISSN: 1001-6058; 1878-0342
• DOI: 10.1007/s42241-022-0057-9

Aquatic vegetations widely exist in natural rivers and play an essential role in the evolution of the water environment and ecosystem by changing the river’s hydrodynamic characteristics and transporting sediments and nutrition. In reality, most aquatic vegetations are highly flexible, which invalidates the “rigid-cylinder” assumption widely adopted in many literatures. To explore the dynamics of submerged flexible vegetation in open-channel flows and its feedback to turbulent flow structures, numerical simulations are carried out using an in-house fluid-structure interaction (FSI) solver. In the simulations, the geometry of vegetation plants is grid-resolved, the turbulent flow is simulated using the large eddy simulation (LES), the dynamics of the flexible plants are solved using the vector form intrinsic finite element (VFIFE) method, and the turbulent flow and the plants are two-way coupled using the immersed boundary (IB) method. The dynamic responses of the flexible vegetation with different plant flexibility, spacing, and submergence are investigated. Simulation results show that flexible plants are subjected to complex flow-induced vibrations (FIVs) rather than static bending. The FIV involves both streamwise and cross-flow motions driven by the small-scale vortex shedding around the plants and the large-scale Kelvin-Helmholtz (K-H) vortices developed in the vegetation canopy layer. The vegetations exhibit pulsive wave motion of different patterns in relatively long and narrow open channels. Compared with the open-channel flows with static plants with equivalent bending deformation, the dynamic responses of flexible plants may increase the turbulent Reynolds stress of the open-channel flow by 70%–100% and increase the invasion depth of the K-H vortices by 30%–50%.