A One-dimensional Stochastic Model of Turbulence within Plant Canopies

Abstract:

The complex nature of turbulence produced by the interaction between plant canopies and atmospheric surface layer winds has been a challenge for the development of reduced-complexity models. The drag force exerted by the canopy elements on the flow field produces profound modifications on the turbulence structure and on the mechanisms of momentum transport. These changes can be characterized by the distribution of sweeps and ejections and can be linked to the skewness of the velocity fluctuation distribution. Second-order closure approaches for the Reynolds-Averaged Navier-Stokes equations yield good predictions for the mean velocity and the turbulence kinetic energy components, but do not include predictions for the skewness of the velocity fluctuation distributions. In this work we adapt a one-dimensional turbulence model to study of canopy flows. The model is based on a one-dimensional version of the filtered Navier-Stokes equations. In the model, the resolved nonlinear and pressure terms are represented by stochastic eddy events, which are implemented as simple mappings. The canopy drag and viscous effects are represented explicitly. The subgrid-scale stresses are parameterized using an eddy-viscosity approach. The resulting equations are solved numerically. Vertical profiles of statistics produced by the model compare reasonably well with experimental data for crops and forests. The model is capable of capturing the main features of the skewness of the streamwise velocity. The model is also extended to study scalar transport within the canopy region. Preliminary results and potential uses of the model are discussed.