Large-Eddy Simulation of Forest Canopy Flows Using the FireStar3D Model: Coherent Structures and Turbulent Kinetic Energy Spectra

Abstract Large-eddy simulations of the development of Kelvin–Helmholtz instability and the transition to turbulence in an atmospheric boundary layer flow over a forest canopy are carried out using FireStar3D’s model. The simulations were conducted by combining five different wind velocities (1, 3, 5, 8, and 12 m s −1 at the canopy top) and three leaf area indices (0.5, 2, and 8) with variable leaf area density. As long as the average wind speed was maintained at the canopy top, it was observed that the flow field was not significantly affected by canopy density, despite the higher drag exerted by the denser canopy. The energy spectrum of the streamwise velocity at the canopy top was analyzed at the steady state. The frequency and wavelength spectra exhibited energy across a wide range of scales, consistent with the characteristics of fully developed turbulence. The main statistical moments and the TKE budgets, obtained using FireStar3D’s model, are in agreement with previously reported experimental and numerical findings. The expected scaling laws of the TKE spectra are predicted in the energy containing range and the inertial subrange, with deviations from the −5/3 scaling law at the high-frequency end of the inertial subrange. This behavior reflects the property of the subgrid-scale (SGS) model and the accuracy of the numerical method used in FireStar3D.