Turbulent Structure of Canopy Flows using Large-Eddy Simulation: Homogeneous and Inhomogeneous Surfaces

University Of California-Davis, Davis CA

Investigators

Abstract

Turbulence accounts for the transport of heat, water vapor, CO2 and other quantities between the surface of the earth and the lower atmosphere. Plant and forest canopies have a strong effect on the wind flowing through them and hence modify the exchange processes. This project is a continuation of work on the distinctive flow patterns (coherent structures) that make a substantial contribution to the exchanges that take place between canopies and the surface layer. The strong velocity gradient at the interface between the canopy and the overlying layer of air induces a relatively high degree of organization to the turbulence, evidenced by strong velocity correlations, high velocity skewness, intermittency, and consistent and repeated flow patterns. Using the computational method of large-eddy simulation (LES), the main objectives of the work are: - Develop methods to visualize and examine the coherent patterns found in computed canopy flow fields. - Create descriptions of coherent structures by constructing a framework of the various elements of which the structures are composed. -Examine the vortex-like nature of the flow structures. - Perform simulations to examine the effects of inhomogeneous conditions, for example at forest edges. - Examine the statistical properties of the flow fields in such transition zones, and also the forces exerted on individual trees, to asses the potential for wind damage. By analyzing the physics of interactions between elements of the plant canopy (foliage, branches, and tree trunks) with the wind, the work provides a basis for explaining transport processes in the canopy.