Near-wall modelling of forests for atmosphere boundary layers using lattice Boltzmann method on GPU

In this work, the simulation and modelling of the turbulent atmospheric boundary layers (ABLs) in the presence of forests are studied using a lattice Boltzmann method with large eddy simulation, which was implemented in the open-source program GASCANS with the use of Graphic\ua0Processing Units (GPU). A method of modelling forests in the form of body forces injected near\ua0the wall is revisited, while the effects of leaf area density (LAD) on the model accuracy is further addressed. Since a uniform cell size is applied throughout the computational domain, the\ua0wall-normal height of the near-wall cells is very large, theoretically requiring a wall function to model the boundary layer. However, the wall function is disregarded here when the forest is modelled. This approximation is validated based on the comparison with previous experimental and numerical data. It concludes that for the ABL conditions specified in this study as well as a large body of literature, the forest forces overwhelm the wall friction so that the modelling of the latter effect is trivial. Constant and varying LAD profiles across the forest zone are defined with the same total leaf area despite the varying one being studied previously. It is found that thetwo LAD profiles provide consistent predictions. The present forest modelling can therefore be simplified with the use of the constant LAD without degrading the model accuracy remarkably