1. Wind and slope contribution in a grassfire second law analysis
E. Guelpa, V. VERDA
(IEEES-9), May 14-17, 2017,
Split, Croatia

2. Fire propagation prediction Fire propagation prediction
INTRO
INTRO
Fire propagation prediction
Fire propagation prediction
Optimize the resources for fire extinction (Ground and aerial means).
Carry out evacuation plans and reduce risk for firefighters.
Reduce risk and improve effectiveness of aerial firefighting.
Models for prediction of:
FIRE FRONT EVOLUTION
EFFECTS OF FIRE ON THE SURRONDING ATHMOSPHERE

3. Fire propagation prediction Fire propagation prediction
INTRO
INTRO
Fire propagation prediction
Fire propagation prediction
FAST SIMULATION MODEL DURING FIRE EVENTS
MULTI-SCENARIO STOCASTIC MODEL
MODEL
DETERMINISTIC APPROACH
PROBABILISTIC APPROACH

4. Fire propagation prediction Fire propagation prediction
INTRO
INTRO
Fire propagation prediction
Fire propagation prediction
PHYSICAL MODELS
EMPIRICAL MODELS
Physics-based approach includes the modelling of the physics and chemistry of fire spread; such models distinguish the different modes of heat transfer (Mell et al 2007)
Semi-empirical models are based on physics of the phenomena but they do not distinguish the modes of heat transfer
Es. BEHAVE, PROMETHEUS
Es. WFDS, FIRESTAR

5. Fire propagation prediction Alternative approach
INTRO
INTRO
Fire propagation prediction
Alternative approach
Landscape propagation model
Reduced 1D model
Physical model

6. Fire propagation prediction Landscape propagation
INTRO
INTRO
Fire propagation prediction
Landscape propagation
1) Convolution of ellipses
fire front at t=t1+dt
fire front at t=t1
2) Composition of wind and slope vectors
Slope
Wind
3) Entropy generation analysis
EGA

7. dS/dt T Φ METHOD Entropy Generation in fire propagation G s
HEAT EXCHANGED WITH THE SURRONDING
MASS FLOW EXCHANGED WITH THE SURRONDING
dS/dt
evaluated as a function of the temperature registered by the thermocouples
TIME DEPENDENT INTERNAL ENTROPY VARIATION T
thermocouple measure Φ
convective + radiative heat flux G
affected by wind and slope values s
UPWIND scheme

8. Full physical simulation
METHOD
Full physical simulation
Numerical simulations have been performed using the software WFDS (Wildland Fire Dinamic Simulator).
This is a three-dimensional simulator developed at NIST that solves the governing equations for buoyant flow, heat transfer, combustion and the thermal degradation of vegetative fuels; turbulence in the gas-phase are solved through LES.
FUEL:
height: 0.2 m
heat of combustion: kJ/kg.
moisture content: 4%, (very dry fuel)
fuel load: 0.5 kg/m2
char fraction: 10%
density of the vegetative fuel: 512 kg/m3.
surface over volume ratio is 4950 m-1.

9. Full physical simulation
METHOD
Full physical simulation
CASE
Wind speed [m/s]
Slope Angle [°] A B 20 C 40 D 2 E 4

10. Fire propagation for different slope values
METHOD
Fire propagation for different slope values
SLOPE
FLAT TERRAIN
UPSLOPE TERRAIN
UPSLOPE TERRAIN
20°
40°

11. Fire propagation for different wind values
METHOD
Fire propagation for different wind values
WIND
NO WIND
Wind intensity
2 m/s
Wind intensity
4 m/s

12. Temperature Evolutions
RESULTS
Temperature Evolutions

13. RESULTS
Terms constituting EG

14. EG for propagation prediction
RESULTS
EG for propagation prediction

15. CONCLUSIONS
Second law analysis is proposed as a way to determine landscape propagation of wildlanland fire events.
The main terms are those related with the exchange of mass, which significantly varies with the considered case, and the one due to the thermal losses.
The total entropy generated in the control volume increases with increasing slope and wind speed.
The total entropy generated is higher in the cases where the propagation occurs faster. This tendency fits better than the relation between fire front velocity and wind velocity/slope.
Future work is focused on the development of a modeling tool based on Entropy Generation

16. THANK YOU FOR THE ATTENTION

17. ACKNOWLEDGEMENTS
This work has been performed within the European Project AF3 - Advanced Forest Fire Fighting. FP7 THEME [SEC ] Preparedness for and management of large scale forest fires. Grant agreement no: