Abstract:

Vegetation in urban environment has various impacts on the micro-climate. Its effect is usually studied in conjunction with urban morphology. In view of the very different length scales, the dynamics around/after a single tree are hardly resolved. As such, the characteristic flows induced by the multiscale structures of the tree are neglected. The mechanism of turbulence production and dissipation in response to a single tree, which is highly multiscale with branches and sub-branches, is conventionally simplified as the parameterization in terms of the leaf area index (LAI, a morphological index). In this connection, the dynamics need to be further examined for reliability.

In this study, fractal tree models, preserving multiscale and scale-invariance features with different geometries, were built. The large-eddy simulation (LES) was used to calculate the winds around the tree. The morphological influences on the flows in the wake were further analyzed. Velocity distribution, momentum transfer, coherent structure, and energy spectrum in the wake were compared, parameterizing the aerodynamic effect on the environment (sheltering and transport ability). The results contrast the dissimilarity of different tree morphologies that improve our understanding of wake dynamics after a single tree.