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FIRETEC and WFDS modeling of fire behavior and smoke in support of FASMEE - Final Report to the Joint Fire Science Program

Author(s): William E. Mell, Rodman Linn
Year Published: 2017
Description:

The objective of FASMEE is to obtain measurements that can be used to evaluate and advance operational smoke models. Among the focus areas listed in the FON task statements are the modeling of fire growth, fire behavior, and plume development. In current operational models, the physical processes driving fire growth, fire behavior, and plume development are not explicitly modeled. These processes are, however, explicitly modeled in physics-based fire behavior models that use the methods of computational fluid dynamics (CFD). Thus, these physics-based fire behavior models, if suitably validated, could be used to help advance operational smoke models. Validation of physics-based fire behavior models, however, requires a wide range of environmental and fire behavior information. Obtaining sufficient information for comprehensive validation of physics-based models through field measurements is challenging – significantly more so than validation of empirically based fire spread models. These measurement challenges are essentially insurmountable for large burn plots with fires that are significantly influenced by local changes in vegetation and wind. Complex ignition procedures increase the measurement challenges. Most FASMEE burn sites are large in area, will use complex “ping pong” ball ignition procedures, and are expected to be of low to moderate fire intensity, typical of prescribed burns. As such, these fires are likely to be influenced by local variations in wind and/or vegetation. In summary, the large area, low to moderate fire intensity, prescribed burns of FASMEE are not suitable for validation of the fire behavior predictions by present-day CFD physics-based models.

Any physics-based fire behavior model using CFD methods can also predict smoke plume rise, due to a heat source that represents a wildland fire, and subsequent downwind transport of smoke. Here, we call this heat source a burner. The burner approach has been used successfully for modeling smoke plumes from burning oil spills. As part of this project, a simple burner demonstration using five different smoke models was conducted. Thus, a range of CFD-based fire behavior and smoke models can be applied to the smoke rise and transport problem by representing the fire as a burner. This facilitates model comparison and model improvement, and provides guidance to measurements needs. Implementing the burner method requires the time history of the heat release rate per unit area (HRRPUA) across the burn plot. This can only be obtained through overhead remote sensing that is suitably calibrated by ground instrumentation. Also, the quantities needed to obtain the HRRPUA can be used to support coarse testing of fire behavior models.

Finally, there is a critical need for the use of geospatial science and technology practices to ensure that the measurements are properly co-located in space and time, quality assured, well documented, and made publicly available in an effective manner.

Citation: Mell, William E.; Linn, Rodman R. 2017. FIRETEC and WFDS modeling of fire behavior and smoke in support of FASMEE. Joint Fire Science Project 16-4-05-1. Seattle, WA: US Forest Service, Pacific Wildland Fire Sciences Laboratory. 37 p.
Topic(s): Smoke & Air Quality, Fire & Smoke Models
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 17022
FRAMES RCS number: 24678
Record updated: Mar 7, 2018