Characterizing Turbulence at a Forest Edge: Comparing Sub-filter Scale Turbulence Models in Simulations of Flow over a Canopy

TL;DR

This study compares two turbulence models, Smagorinsky and Linn, within a fire-atmosphere simulation framework to evaluate their effectiveness in modeling flow over a forest canopy, with implications for wildfire behavior prediction.

Contribution

It introduces a comparison of the Smagorinsky model with the existing Linn turbulence model in a coupled fire-atmosphere simulation environment.

Findings

Smagorinsky model yields similar TKE profiles to the Linn model.

Both models produce comparable turbulent statistics at the canopy edge.

The Smagorinsky model is a viable alternative for LES in fire modeling.

Abstract

In wildfires, atmospheric turbulence plays a major role in the transfer of turbulent kinetic energy. Understanding how turbulence feeds back into a dynamical system is important, down to the varying small scales of fuel structures (i.e. pine needles, grass). Large eddy simulations (LES) are a common way of numerically representing turbulence. The Smagorinsky model (1963) serves as one of the most studied sub-grid scale representations in LES. In this investigation, the Smagorinsky model was implemented in HIGRAD/FIRETEC, LANL's coupled fire-atmosphere model. The Smagorinsky turbulent kinetic energy (TKE) was compared to FIRETEC's 1.5-order TKE eddy-viscosity subgrid-scale model, known as the Linn turbulence model. This was done in simulations of flow over flat terrain with a homogeneous, cuboidal canopy in the center of the domain. Examinations of the modeled vertical TKE profile and turbulent statistics at the leading edge, and throughout the canopy, show that the Smagorinsky model provides comparable results to that of the original closure model posed in FIRETEC.