(570e) Simulation of An Ethylene Wall Fire Using the One-Dimensional Turbulence Model

Lignell, D. O., Brigham Young University
Monson, E. I., Brigham Young University

The mechanism of flame propagation is essential to understand and determine fire spread rates in wildland fires. Recent observations and experiments indicate that in many fires direct contact of flames and unburnt fuel is a dominant mechanism in the propagation of wildland fires, rather than propagation due to radiation alone. Direct contact of flame and unburnt fuel occurs primarily at the interface between burnt and unburnt fuel, where the flame is highly turbulent and unsteady. Therefore, a detailed description of the flame structure at the interface is needed to quantify propagation via direct contact of flame and unburnt fuel. Turbulent flame structures are complex and difficult to model and understand. Turbulent flames involve time and length scales ranging from individual flamelets to full-scale fire. Due to computational costs, full resolution of turbulent combustion is not feasible. Reynolds averaged Navier-Stokes (RANS) and large eddy simulation (LES) are unable to resolve the transient evolution of the flame for all the time and length scales in turbulent flows and rely on sub grid models for closure of averaged and filtered terms. An attractive alternative is the one-dimensional turbulence (ODT) model. This model fully resolves the transient evolution of the flame structure for all the length and timescales in one spatial dimension, and is computationally affordable, allowing many parametric simulations. Turbulence is modeled through eddy events implemented as local rearrangements of the domain, whose size, frequency, and location are specified in a manner consistent with turbulent scaling laws and based on the locally evolving velocity field. ODT has been successfully applied to both reacting and non-reacting turbulent flows. These applications include channel flows, atmospheric flow, and turbulent jet flames. This work extends the ODT model to flame propagation in controlled fires representative of wildland fires. Several different configurations of controlled fires will be simulated to better understand fire propagation in fuel beds. This presentation focuses on the simulation of a porous wall, ethylene fire, where the ethylene is continuously introduced through the pores in the wall. This simulation provides resolved statistics of intermittent turbulence, including flame structure and temperature, velocity, and composition profiles. This information can be used both to investigate physical processes involved in flame propagation, and to develop models for use in larger scale simulations. Validation of the simulation will be presented by comparison to experimental data provided by the USDA Forest Service.