Plant canopy representation in Large-Eddy Simulation using a one-dimensional stochastic wall model

Abstract:

In the atmospheric boundary layer (ABL), the presence of a plant canopy significantly changes the dynamics of the flow and these changes can have an important impact on the turbulent transport of momentum, heat, gases and particles. In numerical studies using the Large-Eddy Simulation (LES) technique, resolving the flow inside the canopy requires fine grid resolutions. For simulation of the entire ABL, this can lead to high computational cost. In coarser LES and in large-scale atmospheric models, the effect of the plant canopy is usually represented as a roughness length scale applied to the wall model. However, the effect of plants in turbulent transport is much more complex than a simple “enhanced roughness”. In this work we evaluate the use of the One-Dimensional Turbulence (ODT) model as a wall model for LES of ABL flows. In particular, we focus in application in which the flow inside and immediately above the canopy is resolved in the ODT model, which is then two-way coupled with a coarser LES. The ODT model resolves the filtered 1-dimensional version of the Navier-Stokes equation in the vertical direction, replacing the non-linear term with a stochastic representation of eddies. In order to use the ODT to represent the canopy flow, a sub-grid scale eddy viscosity model was developed, and the effects of plant canopy and atmospheric thermal stability on the flow were included. The use of the LES-ODT coupling to represent different types of plant canopies is discussed.