The Role of Vorticity and Fuel Moisture on the Near-Field Plume Structure and Ember Dynamics
Dr. Bryan Quaife | Florida State University
The processes that managers use to control smoke production and dispersion are poorly understood. The overall goal of this project is to improve the understanding of feedbacks between prescribed fire practices that are both heterogeneous and dynamic, and the near-field plume organization for low intensity, small scale (<100 hectare [ha]) wildland fires, which includes the vast majority of prescribed fire and wildfires on Department of Defense (DoD) lands. More specifically, this project will provide a scientific-basis for identifying opportunities to engineer prescribed fires to produce desired plume dynamics, smoke dispersion, and quantifiable risk of ember-ignited spot fires. It will improve understanding interacting factors of burn plot configuration, ignition pattern, fuel moisture, site-specific vegetation, and meteorological conditions. A combination of multi-scale modeling, new model development, and high-resolution measurements will characterize the dependence of convective core distributions and strength on 3D entrainment and heat-release patterns, ambient fuel, and wind conditions. Specific objectives include: (1) developing a better understanding of the influences of canopy structure, edge effects, and associated surface boundary layer flow on the near-fire plume; (2) characterize heat exchange and moisture dynamics influencing the transport of embers and their spot fire ignition efficiency; (3) focused field studies to analyze plume dynamics and to validate models; and (4) developing simplified data-driven models needed to quantify uncertainty and improve ember and smoke dispersion predictions.
The project will first use novel data analysis techniques to mine new information from existing experimental data and high-fidelity coupled fire atmosphere simulations to identify key correlations between near-field environmental conditions and updraft characteristics at scales from 100 meter squared [m2] - 1 ha scales. High-resolution measurements of the entrainment wind patterns and near-field plume structure will be used to (1) test multi-physics, simplified, and data-driven model fidelity; (2) identify key phenomenology that drives fire-induced flow and moisture through multi-scale (canopy, burn unit, and boundary layer) physics-based modeling; and (3) provide data including adequate wind characterization and sensitivity analysis for prescribed fire plume model development. The modelling component will focus on existing dispersion models (Daysmoke), and developing new high-fidelity computational fluid dynamics (CFD), heat transfer, and energy balance models that describe the most important factors including fuel moisture, solar radiation, naturally occurring complex structures such as the canopy, fuel bed, and plume shading. Simplified models that capture the basic physics will be developed for optimization and to estimate probability distributions and correlations of key parameters.
This project will lead to better smoke management and risk management on DoD lands by investigating key factors that affect near-field plume structure and dynamics at scales common to DoD managed fires. Particular parameters that will be investigated include canopy structure, fuel moisture, and ambient atmospheric conditions. Model improvements will facilitate transitioning results to managers by directly improving smoke dispersion of low-intensity or small-scale (<100 ha) surface fires and ember transport that are heavily influenced by near-field dynamics not accounted for in current tools.