Numerical study of submerged bending vegetation under unidirectional flow

Abstract

Submerged vegetation commonly grows and plays a vital role in aquatic ecosystems, but it is also regarded as a barrier to the passing flow. Numerical simulations of flow through and over submerged vegetation were carried out to investigate the effect of vegetation density on flow field. Numerical simulations were computationally set up to replicate flume experiments, in which vegetation was mimicked with flexible plastic strips. The fluid–structure interaction between flow and flexible vegetation was solved by coupling the two modules of the COMSOL packages. Two cases with different vegetation densities were simulated, and the results were successfully validated against the experimental data. The contours of the simulated time-averaged streamwise velocity and Reynolds stress were extracted to highlight the differences in mean and turbulent flow statistics. The turbulence intensity was found to be more sensitive to vegetation density than the time-averaged velocity. The developing length increased with the spacing between plants. The snapshots of the bending vegetation under instantaneous velocity and vorticity revealed that flexible vegetation responded to the effects of eddies in the shear layer by swaying periodically. The first two rows of vegetation suffered stronger approaching flow and were prone to more streamlined postures. In addition, the origin of tip vortices was investigated via the distribution of vorticity. The results reveal the variation of flow properties with bending submerged vegetation and provide useful reference for optimization of restoration projects.

Keywords

• Computational fluid dynamics
• Fluid–structure interaction
• Turbulence
• Flexible and submerged vegetation