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

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

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

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

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

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

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

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: 18500 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.

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

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

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

Temperature Evolutions RESULTS Temperature Evolutions

RESULTS Terms constituting EG

EG for propagation prediction RESULTS EG for propagation prediction

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

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ACKNOWLEDGEMENTS This work has been performed within the European Project AF3 - Advanced Forest Fire Fighting. FP7 THEME [SEC-2013.4.1-6] Preparedness for and management of large scale forest fires. Grant agreement no: 607276