On the existence of a steady state regime for slope and wind driven fires
Domingos X. ViegasCentro de Estudos sobre Incêndios Florestais–Associação para o Desenvolvimento da Aerodinâmica Industrial, Universidade de Coimbra, Apartado 10131, 3031-601 Coimbra, Portugal. Telephone: +351 239 79 07 32; fax: +351 239 79 07 71; email: xavier.viegas@dem.uc.pt
International Journal of Wildland Fire 13(1) 101-117 https://doi.org/10.1071/WF03008
Submitted: 13 February 2003 Accepted: 23 September 2003 Published: 8 April 2004
Abstract
Forest fire behaviour analysis and prediction is based on the assumption that for a given set of boundary conditions a steady-state of fire propagation exists with a well-defined rate of spread. The evolution of a fire front for linear and point ignited fires is analysed and it is shown that, even in nominally uniform and permanent conditions, the rate of spread of the head fire does not remain constant in the general case of slope- and wind-driven fires due to joint convection and radiation effects. The basic case of a linear fire front without slope and without wind is one of the few cases for which the rate of spread is well defined and remains constant. if there is slope or wind in point ignition fires, the rate of spread of the head fire tends to increase while for linear ignition fires the contrary happens. It is shown that convective effects induced by the fire for steep slope terrain can produce the so-called ‘blow-up’ effect even in the absence of any other special atmospheric conditions. Therefore the definition of rate of spread of a fire and its evaluation from laboratory and field experiments is strongly questioned.
Additional keywords: fire behaviour; modelling slope and wind effects; fire dynamics; fire growth; fire acceleration; convective effects; ‘blow-up’; canyon fires.
Acknowledgements
The author thanks his co-workers who performed the laboratory experiments used in this study for their contribution. Particular thanks are given to Luis P. Pita, Pedro Palheiro, Luís Mário Ribeiro, Miguel Batalha, Luís Maricato, Nuno Luís and A. Cardoso. The work described in this article was carried out as part of the research program of projects SPREAD (Contract EVG1-CT-2001–00043) and WINSLOPE (Contract POCTI/34128/EME /2000) supported respectively by the European Union and by the Fundação para a Ciência e Tecnologia. Their support is gratefully acknowledged. Comments and suggestions made by anonymous reviewers helped a lot in improving the quality and clarity of this article and are therefore gratefully acknowledged by the author.
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