식생 가지가 침수식생 난류흐름 구조에 미치는 영향 분석

Vegetation significantly influences flow structure and mixing characteristics in open channels, and its morphological features induce complex turbulent structures. This study quantitatively investigates the effects of vegetation branching on turbulence and mixing by comparing two submerged vegetation models, which are without branches (Type I) and with branches (Type II). In the Type II model, a sharp velocity gradient developed near the vegetation top, resulting in a thinner momentum thickness and reduced momentum transfer from the free stream region to the vegetation zone. The presence of branches induced small-scale vortices that enhanced turbulent kinetic energy and Reynolds stress in Type II compared to Type I, while shear production near the vegetation top was higher in Type I. These results suggest that turbulence generated by branches partially replaces turbulence production driven by shear in Type II, leading to the suppression of coherent vortex structures at the vegetation top. This structural change in turbulence also influenced the distribution of turbulent diffusion coefficients, as the vertical diffusion coefficient in Type II decreased to approximately 70% of that in Type I at the vegetation top. Furthermore, the ratio of transverse to vertical diffusion coefficients was higher within the vegetation zone in Type II, indicating that lateral mixing of pollutants or suspended particles may be more dominant than vertical mixing when branches are present.