Numerical simulation of the interaction between two fire fronts in the context

of suppression fire operations

D. Morvan⁽¹⁾, Chad Hoffman⁽²⁾, F. Rego⁽³⁾, W. Mell⁽⁴⁾

(1) Laboratoire de Mécanique, Modélisation et Procédés Propres (M2P2)

UNIMECA Technopôle de Château Gombert 60 rue Joliot Curie

13453 Marseille cedex 13 France, Email : dominique.morvan@univmed.fr

(2) Department of Forest Resources College of Natural Resources

University of Idaho Moscow ID-USA

(3) ISA-CEABN Tapada da Ajuda 1349-017 Lisbon Portugal

(4) BFRL-NIST 100 Bureau Drive, Gaithersburg MD-USA

This paper deals with the study of the physical phenomenon observed between two converging fire fronts (a head fire and a back fire), in conditions similar to those encountered during a suppression fire operation. The simulations were carried out using two fully physical models (FIRESTAR, WFDS) [1, 2], including the resolution of the set of balance equations (mass, momentum, energy …) governing the behaviour of the coupled system formed by the vegetation and the surrounding atmosphere. The numerical results showed clearly that before that the two fire fronts merged at a meeting zone, they interacted together, modifying mutually their behaviour. One phenomena contributing to this interaction, was the existence of an in draft flow located ahead of the head fire, contributed to the fact that, at some distance from the head fire, the back fire seemed to be aspirated, before that the two fire fronts merged together (see Figure 1).

Figure1: Temperature and velocity vectors calculated during the propagation of a head

(on the left) and a back fire (on the right) in a grassland (20s separated the two images)

References:

[1] D. Morvan, J.L. Dupuy. Modelling the propagation of a wildfire through a Mediterranean shrub using a multiphase formulation. Combustion & Flame, 138: 199-200, 2004.

[2] D. Morvan, S. Méradji, G. Accary. Physical modelling of fire spread in Grasslands. Fire Safety Journal, 44: 50-61, 2009.