MMM SEMINAR NCAR
Modeling of Wildland Fires
Due to the constraints upon the
computational power, fluid dynamical physically–based numerical fire models,
such as FDS and its extension (WFDS), are not yet suitable for
faster--than--real--time applications and still remain in the research mode.
This type of wildfire models is important tool to improve our understanding of
the wildland fire and the accuracy of less
physically-based numerical models and operational models. However before using
these models to study wildfire, validation is necessary. Plume theory and data
from the Meteotron experiment are used to evaluate
the fire plume properties simulated by the WFDS. The study indicates that the
WFDS produces good agreement in plume properties with the Meteotron
results. The WFDS also used to simulate the grass fire experiments conducted in
Using the WFDS as a benchmark, the WFDS and UULES-wildfire coupled
model are used to simulate the same Australian experimental grass fires. The
simulation results by UULES-wildfire coupled model compared reasonably well
with the WFDS simulations and fire experiments in terms of frontal fire spread
rate.
Finally, UULES-wildfire coupled model is used to simulate the grass fires in the turbulent convective boundary layer (CBL). A number of simulations are completed to examine effect of turbulence on grass fire evolution. In each simulation, multiple grass fires of the same size are ignited at the same time but the different locations of the domain. The fires evolve very differently. The difference in the area burnt can be as much as a factor of two at the end of the simulations. The results suggest that fire spread is not deterministic: similar to hurricane forecasts, a probabilistic forecast is warranted. The uncertainties introduced by PBL turbulence/gustiness may be larger than the uncertainties in the fire spread formulas used in operational models like FARSITE. The development of blow-up fires may have a significant random component. Sudden increases in fire intensity may be a result of a random conjunction of a fire and boundary layer eddy that is favorable for fire growth. One of the most important factors that determine how fast a grass fire spread in a CBL is the initial ambient wind condition adjacent to the fire.
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NCAR-Foothills Laboratory
Bldg 2 Auditorium (Rm1022)