Near-Wall Representation in Large-Eddy Simulation Using a One-Dimensional Stochastic Model

In Large-Eddy Simulation (LES) of high-Reynolds-number flows, such as the atmospheric boundary layer (ABL), the interaction between the flow and the surface must be parameterized in order to keep computational costs low. Although many wall models are available, they typically rely on the mean behavior of canonical flows, without the flexibility needed to represent the diverse set of conditions present in the ABL. In this study we test the One-Dimensional Turbulence (ODT) model as a wall model for LES of ABL flows. In this approach, ODT is used to represent vertical exchanges between columns in the LES grid and the surface. To keep the computational cost of the wall model reasonable, a filtered version of ODT is used, which includes a dynamic subgrid-scale modeling approach based on the Germano identity. In this two-way coupling framework, while both LES and ODT simulate the time evolution of filtered flow and scalar fields, in the ODT the vertical turbulent flux is represented by a sequence of stochastic mapping processes that mimics the effects of turbulent eddies. In spite of this stochastic behavior, all variables simulated by ODT represent instantaneous fields in a turbulent flow, making ODT a useful tool to incorporate complex near-wall phenomena in LES (such as chemical reactions and particle emission/deposition processes). The presence of elements at the surface, such as vegetation and urban environments, can also be included in the ODT framework using similar approaches as employed in LES. We test the performance of ODT as a wall model for the flow field itself, in addition to the temperature, scalar and particles fields, by comparing it with other standard wall models. Simulations of ABL in unstable and stable conditions, as well as simulations with canopy, are evaluated and compared with field data, and advantages of the ODT-LES coupling are discussed. Simulation results show reasonable agreement with observations, making the ODT wall model a viable approach for atmospheric-surface exchanges representation in LES.