1. Entropy generation transient analysis of a grassfire event through numerical simulation
E. Guelpa V. VERDA
(IEEES-9), May 14-17, 2017,
Split, Croatia

2. INTRO
Any connection?
ENTROPY GENERATION
FIRE PROPAGATION

3. Fire propagation prediction Fire propagation prediction
INTRO
INTRO
Fire propagation prediction
Fire propagation prediction
EMPIRICAL
MODELS
PHYSICAL
MODELS
DESPITE DECADES OF RESEARCH ON FOREST FIRES,
THERE ARE ALREADY NO COMPLETELY VALUABLE TOOL
FOR THE FIRE PROPAGATION PREDICTION.
MODEL RESULTS AFFECTED TO ERRORS
PROBABILISTIC APPROACH HAVE TO BE USED TO OVERCOME MODEL INACCURACY

4. INTRO
Any connection?
ENTROPY GENERATION
FIRE PROPAGATION

5. Fire propagation prediction Entropy Generation Approach
INTRO
INTRO
Fire propagation prediction
Entropy Generation Approach
INCREASE
DEVICES
PERFORMANCE
DESCRIBE
NATURAL
PROCESSES

6. INTRO
Any connection? ?
ENTROPY GENERATION
FIRE PROPAGATION

7. Full physical simulation
METHOD
Full physical simulation
A numerical simulations have been performed using the software WFDS
(time-dependent and three-dimensional prediction of the fire propagation)
This model accounts for :
two dimensional fire transportation along the terrain (heat transfer, combustion, buoyant flow, the thermal degradation of vegetative fuels and Turbulence in the gas-phase with LES)
natural convection involving the plume above the fire area and the consequent air flow towards the fire.
16 m
16 m
32 m
Very high computational costs are required
(more than 1day / 2 min simulation)

8. Full physical simulation
METHOD
Full physical simulation
TEST
slope
direction NNE
18°
16 m
16 m
SLOPE
32 m
height h
0,2 m
heat of combustion H
18500
kJ/kg
moisture content x
0,04 -
fuel load
0,5
kg/m2
char fraction c
0,1
density ρ
512
kg/m3
surface over volume ratio σ
4950
m-1
WIND
Wind intensity
2 m/s

9. HOW FIRE PROPAGATES IN THESE CONDITIONS
METHOD
Full physical simulation
slope
direction NNE
18°
SLOPE
WIND
Wind intensity
2 m/s ?
HOW FIRE PROPAGATES IN THESE CONDITIONS

10. LUMPED PARAMETER APPROACH
METHOD
Entropy Generation in fire propagation
LUMPED PARAMETER APPROACH
The entropy generation analysis has been carried out for each control volume along the fire front.
Each Control Volume is centered
in a thermocouple
The CV length is taken as the space
that the flame travel in a time equal
to the thermocouple sampling time

11. 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
Depending on wind-slope direction values s
UPWIND scheme

12. Terms constituting EG RESULTS NOT SIGNIFICANT SIGNIFICANT SIGNIFICANT
HIGHER IN THE FLANKS WHERE TEMPERATURE IS LOWER
HIGHER AT THE CENTRE, WHERE MASS FLOW RATES AND TEMPERATURE ARE HIGHER

13. highest Entropy Generation in the area where the spead is faster
RESULTS
EG along the fire front
highest Entropy Generation
in the area
where the spead is faster

14. ENTROPY GENERATION FOR PREFERENTIAL PROPAGATION PATHS
RESULTS
EG for propagation prediction
EG estimates the spread velocity very well
In this flank spreading against the wind and slope direction EG is not able to correctly estimate the fire propagation velocity
EG slightly overestimate
the maximum
spread velocity
BACKFIRE
ENTROPY GENERATION FOR
PREFERENTIAL PROPAGATION PATHS
EG satisfactorily estimates the spread velocity

15. EG for propagation prediction
RESULTS
EG for propagation prediction
ENTROPY GENERATION PREDICTS THE FIRE FRONT EVOLUTION MORE ACCURATELY THAN THE 1D MODEL BASED ON SIMPLE VECTOR COMPOSITION

16. ? CONCLUSIONS Entropy Generation and fire propagation prediction
ENTROPY GEN IS HIGHER WHERE THE SPREAD IS HIGER
RELATIONSHIP BETWEEN MAXIMUM ENTROPY GENERATION AND WILDFIRE PROPAGATION
TERM RELATED TO THE ENTROPY TIME VARIATION IS LESS SIGNIFICANT COMPARED TO THE OTHERS
ENTROPY GEN ANALYSIS FOR A GRASSLAND FIRE FRONT ?
MAX ENTROPY GEN ALLOWS TO DETECT THE MAIN PROPAGATION DIRECTION
3D FULL SIMULATION FOR DATA EVALUATION

17. Thank you for the attention
(IEEES-9), May 14-17, 2017,
Split, Croatia

18. 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: