Near-wall approximations to speed up simulations for atmosphere boundary layers in the presence of forests using lattice Boltzmann method on GPU

TL;DR

This paper presents a GPU-accelerated lattice Boltzmann simulation platform for atmospheric boundary layers with forests, achieving accurate results efficiently by modeling forest effects as body forces near the wall without wall-functions.

Contribution

The study introduces a fast, accurate GPU-based lattice Boltzmann method for simulating forest-influenced atmospheric boundary layers, eliminating the need for wall-functions.

Findings

Simulation results match experimental and finite volume data.

Good accuracy achieved without wall-functions due to forest force modeling.

GPU acceleration significantly reduces computation time.

Abstract

Forests play an important role in influencing the wind resource in atmospheric boundary layers and the fatigue life of wind turbines. Due to turbulence, a difficulty in the simulation of the forest effects is that flow statistical and fluctuating content should be accurately resolved using a turbulence-resolved CFD method, which requires a large amount of computing time and resources. In this paper, we demonstrate a fast but accurate simulation platform that uses a lattice Boltzmann method with large eddy simulation on Graphic Processing Units (GPU). The simulation tool is the open-source program, GASCANS, developed at the University of Manchester. The simulation platform is validated based on canonical wall-bounded turbulent flows. A forest is modelled in the form of body forces injected near the wall. Since a uniform cell size is applied throughout the computational domain, the averaged first-layer cell height over the wall reaches to $\langle \Delta y^+\rangle = 165$. Simulation results agree well with previous experiments and numerical data obtained from finite volume methods. We demonstrate that good results are possible without the use of a wall-function, since the forest forces overwhelm wall friction. This is shown to hold as long as the forest region is resolved with several cells. In addition to the GPU speedup, the approximations also significantly benefit the computation efficiency.