Physics-Based Modeling of Fire Behavior and Smoke Plume Development, How Much is Enough?
William Mell | U.S. Forest Service
The use of prescribed fire is essential to land management of Department of Defense (DoD) installations. The planning of such fires requires the assessment of their potential to negatively impact the air quality and visibility on downwind communities and road systems. Smoke dispersion models commonly used in this assessment are designed to predict large-scale (long range) smoke transport. The modeling of near-fire processes and features, such as the fire-atmosphere interaction and near-fire plume rise, is highly simplified, leading to inadequate predictions of the local smoke impact. Physics-based fire behavior models exist that simulate the local processes with much higher physical fidelity but they require specialized knowledge and significant computational resources to employ. The physics-based Wildland-urban interface Fire Dynamics Simulator (WFDS-PB) is one such model/simulator. The objective of this project is to investigate, through model comparison, the practicality of applying a simplified version of WFDS-PB to predict the evolution of wildland fire fronts, fire-atmosphere interactions, and the resulting near-fire smoke plume development for the purpose of planning prescribed burns of interest to the DoD.
The project will assess the capability of simplified physics models to capture the development of buoyant smoke plume(s) and dynamic fire behavior by comparing model predictions from the full-physics WFDS-PB simulator and a reduced physics version of WFDS-PB, called WFDS-LS. The WFDS-LS model uses simplified approaches for modeling the gas-phase combustion and fire spread within the same computational fluid dynamics solver used by WFDS-PB. The capability of WFDS-LS will be assessed across a range of scenarios in order to investigate the influence of the simplifying assumptions in isolation (e.g., the dynamics of combustion-driven buoyant flow) and under more complex conditions that requiring a coupling of physical process (e.g., fire line and buoyant plume interaction). The focus of this project is on model comparison. Some evaluation of WFDS-PB smoke plume rise simulation has been conducted for relatively simple scenarios. Evaluation of model predictions of plume rise and near fire smoke transport for scenarios characteristic of realistic prescribed burns (such as complex ignition patterns) of interest to the Strategic Environmental Research and Development Program (SERDP) requires appropriate datasets that are largely lacking in the literature. Ongoing SERDP-funded efforts and potential future experimental burns (e.g., Fire and Smoke Model Evaluation Experiment [FASMEE] 2018) may provide suitable datasets for model evaluation.
This project will demonstrate the capability of various reduced-physics models of wildland fire, as compared to full-physics simulations, to model coupled fire spread and smoke plume evolution. Scientific understanding will be advanced by identifying, in the scenarios to be examined, modeling approximations essential and non-essential to preserving the predictions of the full-physics simulations. This understanding, in turn, will guide future development and deployment of improved software tools for the planning of prescribed fires for management of DoD lands.