Forest fire management using CFD
June 27, 2003
Forest fires cost the United States billions of dollars in
property and land loss annually, and of course are responsible
for the deaths of numerous fire fighters and civilians. In
addition, the US has suffered a number of aviation disasters
that have occurred in attempting to extinguish the infernos.
It has long been the aim of researchers in forest fire management
to find a way of predicting the likely ignition locations
of these fires, as well as how they might spread. Now, a
team of engineers and scientists at the Forest Service’s
Fire Sciences Laboratory in Missoula, Montana is using computational
fluid dynamics from CD-adapco to give them the answers they
need.
The Fire Sciences Laboratory in Missoula is a world leading
facility for research on wildland fire. The laboratory uses
the latest science and technology to understand fire and
smoke behavior and the effects of fire in order to manage
better the forests and rangelands of the US and around the
world.
Sophisticated solver
Fire differs significantly in its behavior from other fluids
and gases due to its complex chemical, thermal and turbulent
behaviour and interaction. Because of this complexity, any
simulation tool must be capable of handling the chemical
reactions; the turbulent flows and radiative and convective
heat transfer within the analysis.
The Fire Sciences Lab has chosen to use STAR-CD from CD-adapco.
This sophisticated CFD solver is used as the building block
for the flow analysis and integrates with the Fire Sciences
Lab’s own fire growth simulation model, FARSITE. In
this way, the expertise of the Fire Scientists and the CFD
developers are coupled through the software to overcome the
challenges of predicting the spread of fire over large topographical
areas.
STAR-CD is the latest weapon in the Lab’s armoury of
simulation tools, which includes an instrumented wind tunnel
burn-rig capable of burning a range of solid fuels in a controlled
environment. In an effort to correlate the combustion and
turbulence models required to predict this chaotic flow domain,
the fire growth data in the wind tunnel is being compared
to predictions performed using STAR-CD.
Coupled solution
Analyses carried out by the Forest Service have involved
the study of the flow of large air masses over topographical
domains. Using satellite-based digital elevation map (DEM)
data, this landscape surface can be read automatically into
STAR-CD to provide an immediate shell representation of the
ground surface. CD-adapco worked together with the Fire Sciences
lab to develop this automated process to build the computational
model based on the DEM data. Once the environmental conditions
had been added, namely the measured wind velocities in both
3D spatial and time frames, the analysis was run and the
results were post-processed all within STAR-CD.
The ability of STAR-CD’s modular framework to interact
with third party codes and in-house software has been a major
benefit for the scientists and engineers at the Fire Research
Centre. Using CFD as the backbone of their computational
effort, the engineers can make more of their existing in-house
codes by linking them directly to STAR-CD, producing a coupled
solution suited to these highly specific problems.
Some validation work has already been completed at the Fire
Sciences lab which has shown that the coupling of CD-adapco's
software with the Fire Sciences fire-growth models can more
accurately predict the spread of fire growth as compared
to any other tools available. This is highly significant
as validation of the models is key to its implementation
as a tool in the fire fighter's armoury.
Point of ignition
With continuing work and refinement of the models at the
Fire Sciences Lab, it is possible accurately to simulate
the spread of a fire over a large region. With the inclusion
of solar radiation models and other features, it is also
possible to identify areas of extreme risk to fire ignition.
However, the actual point of ignition is still governed to
a large extent by random events such as lightning strikes
and camping fires.
The team at the Fire Sciences lab is excited at the prospect
of using the software in real applications to manage active
fire situations. It is envisaged that reports of fire outbreak
will be provided to the Fire Sciences Lab, which will then
initiate an analysis using the software and, in turn, predict
the growth of the fire. On a geographically smaller scale,
the Laboratory is also using the software to predict how
topography (such as angle of slope) might affect the spread
of fire.
Life saver
In the future, the Laboratory will expand the application
of the software to include the analysis of local buoyancy
effects due to fire progression and also the impact of solar
radiation on mountain slopes, which can act as a catalyst
in the spread of vegetation fire.
The information gathered by the Laboratory using STAR-CD
can be used to determine how best to control fires and manage
their spread using controlled burning. The success of a predictive
tool within this area of research will have a significant
impact, and with the ultimate goal being to save lives, the
information available to the Fire Sciences Laboratory from
this new approach is being welcomed by all those in fire
management.
| 
