Turbulence affected by submerged aquatic vegetation under wind-induced flow
Chenhui Wu, Jiang Deng, Xiaojie Zhou, Ang Gao, Kedong Feng, Chunyue Zhu
Abstract
Submerged aquatic vegetation (SAV) changes the turbulent structure of rivers, wetlands, estuaries, and lakes. However, few studies have focused on the influence of SAV on hydrodynamic characteristics under wind-induced flow. Therefore, laboratory experiments were conducted to study the effects of SAV on the flow structure and turbulence characteristics under wind-induced flow, and spectral based decomposition method was used to separate turbulence and wave velocity. Result shows that SAV reduced local velocity within canopy and elevates the location of the zero-velocity point. The canopy drag caused by SAV increases the decay rate of turbulent Reynolds stress along depth while hardly influencing wave Reynolds stress. Canopy drag depresses the turbulent RMS (root mean square) velocity and wave orbital velocity. The presence of SAV leads to the decrease in TKE (turbulent kinetic energy) production and dissipation rate within canopy. The canopy drag more effectively diminishes TKE production than it does the dissipation. Research on local isotropy of SAV in wind-induced flows shows that the presence of SAV promotes a gradual transition from local anisotropy to local isotropy in turbulence within canopy. Finally, quadrant analysis reveals that the presence of SAV reduced the probabilities and the contribution to turbulent momentum of ejection and sweep.