LES analysis of turbulent boundary layer over 3D steep hill covered with vegetation

Large eddy simulation (LES) is carried out to investigate the turbulent boundary-layer type of flows over a hill-shaped model with a steep slope. Also, we focus on the surface condition of a hill, such as vegetation effects as well as curvature effects. In order to model the vegetation effects for LES, we employ the feedback forcing method proposed by Goldstein et al. (1993, Modeling a no-slip flow boundary with an external force field. J. Comput. Phys. 105, 354–366). In this model, the equation of motion for trees or grasses are coupled with the Navier–Stokes equation, so turbulence in the vegetation canopy can be numerically expressed. Instantaneous velocity profile of turbulent boundary layer on the corresponding surface is imposed at inflow boundary. Both the computed results over the hill with and without vegetation are in good agreement with Meng and Hibi's (1998. An experimental study of turbulent boundary layer over steep hills. In: Proceedings of 15th National Symposium on Wind Engineering, pp. 61–66.) experimental data for a rough and a smooth hill. Also, the effects of vegetation on turbulence statistics, such as high intensity due to the coherent flow structures at the top of the vegetation and reduction of turbulence inside the vegetation, are clarified.