# Large-Eddy Simulation of Flow Over a Vegetation-Like Canopy Modelled as Arrays of Bluff-Body Elements

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## Abstract

Turbulent flow over a vegetation canopy under neutral atmospheric conditions is investigated using large-eddy simulation. Each model tree, which consists of a sphere-shaped tree crown and a cylindrical trunk, is fully resolved. The resulting turbulence statistics and the drag force on the vegetation agree well with measurements from the corresponding wind-tunnel experiment described by Böhm et al. (Boundary-Layer Meteorol, 146:393–419, 2013). Statistically, this kind of model canopy exhibits both vegetation and bluff-body-flow characteristics. The time-averaged flow skims over the top of the underlying canopy, forming a low-momentum recirculation zone on the lee-side of the bluff elements, which causes significant dispersive stress within the canopy layer. Two other numerical representations of vegetation canopies, referred to as the drag-element and drag-crown approaches, have also been developed to assess the performance of simulations. Turbulence statistics suggest that the canopy shear layer interferes with wakes behind stems and crowns. The drag-crown approach yields better agreement between numerical results and experimental measurements than does the traditional drag-element approach, thus providing a promising numerical model for simulating canopy turbulence.

### Keywords

Canopy representation Canopy turbulence Large-eddy simulation Vegetation## Notes

### Acknowledgements

The work was supported by the National Natural Science Foundation of China under Grant Nos. 11322221 and 11132005, and the Ministry of Science and Technology of China under Grant No. 2015DFA20870. The authors would also like to thank the Tsinghua National Laboratory for Information Science and Technology for the support in parallel computing.

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