Wind tunnel generation of horizontal roll vortices over a differentially heated surface

Haines, Donald A.; Smith, M. C.

doi:10.1038/306351a0

Cited by 22 publications

(4 citation statements)

References 7 publications

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“…3). The Sakami moraine is a 500 km long series of glaciofluvial sand plains that formed at the margin of the Laurentide ice sheet during drainage of Glacial Lake Haines (1982) and Haines and Smith (1983)). Narrow unburned treecrown strips (white lines; right diagram) outline successive fire perimeters in a forest otherwise completely burned to black (grey shading).…”

Section: Study Areamentioning

confidence: 99%

“…This is substantiated by more recent data showing that the residence time of the flame at the trunk base during a free-moving surface fire tends to be longer on the leeward side than on the windward side of the trunk and that the height and temperature of the flame standing on the leeward side of a tree tend to be greater than in the freemoving flame (Gutsell and Johnson 1996). These downward air movements possibly result of horizontal-roll vortices that develop parallel to the wind direction along fire flanks (Haines and Smith 1983). Repetition of this phenomenon during fire spread produces a series of ellipsoid strips delineating successive fire perimeters (Wade and Ward 1973;Foster 1983;Simard et al 1983).…”

Section: Introductionmentioning

confidence: 97%

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Impact of fire behavior on postfire forest development in a homogeneous boreal landscape

Arseneault¹

2001

Can. J. For. Res.

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Although behavior of stand-replacing wildfire has significant impacts on initial tree regeneration in the fireprone boreal landscape, the unknown behavior of most past wildfires has precluded any evaluation of these impacts on the progressive development of late-successional forest ecosystems. In this study, the effects of fire behavior on longterm ecosystem development were evaluated by linking the banding pattern of tree density in a jack pine (Pinus banksiana Lamb.) -black spruce (Picea mariana (Mill.) BSP) forest on a flat and homogeneous landform in northern Quebec to a similar, previously documented pattern of unburned strips of tree crowns. Complex wildfire-atmosphere interactions during the spread of a 1941 stand-replacing wildfire created this pattern in stem density, most likely by differentially damaging the canopy-stored seed bank between areas of contrasting fire severity. Sites with initial differences in seedling densities have followed different recovery pathways and developed markedly different forest structures, as well as differences in species abundance. Compared with areas of severe crown fire, the present-day vegetation in areas of low crown fire severity shows a higher density of living pines in the canopy layer, higher spruce and dead pine densities in the subcanopy layer, a lower pine density in the understory layer, and a higher abundance of Cladina rangiferina (L.) and Cladina stellaris Opiz (Brodo) in the lichen mat. This close spatial connection between crown fire severity and the ecological processes driving ecosystem recovery may explain large differences in vegetation among sites in the boreal landscape.Résumé : Dans la zone boréale qui est soumise à un régime de feux létaux et récurrents, le comportement des incendies a un impact important sur la régénération après-feu des conifères. Toutefois, le manque de données sur les feux passés empêche d'étudier l'effet du comportement de ces feux sur l'historique de développement des forêts aujourd'hui matures. Dans le présent travail, les effets du comportement des incendies sur le développement à long terme des écosystèmes forestiers ont été évalués à partir du lien existant entre un patron de densité des tiges de pin gris (Pinus banksiana Lamb.) et d'épinette noire (Picea mariana (Mill.) BSP) dans un paysage plat et uniforme du nord de la forêt boréale au Québec et un patron, déjà observé ailleurs, de bandes de cimes épargnées par les feux. Des interactions complexes entre les conditions atmosphériques et la propagation d'un feu sévère en 1941 ont créé ce patron de densité des tiges, fort probablement en endommageant à différents degrés la banque de graines contenue dans la cime des arbres. Les sites présentant des différences initiales de densité de plantules ont suivi des patrons de développement distincts, de telle sorte qu'ils montrent aujourd'hui des écarts importants de structure et d'abondance specifique de la forêt. En comparaison des sites soumis à un feu de cimes sévère, les sites soumis à un feu de cime de faible sévérité aff...

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Section: Study Areamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Impact of fire behavior on postfire forest development in a homogeneous boreal landscape

Arseneault¹

2001

Can. J. For. Res.

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“…Large arrays of contra-rotating 'roll vortices' are generated in many kinds of forced-convection buoyant flows, but are again likely to be significantly different in structure from skew-induced vortex pairs. A buoyancy-driven vortex pair with common flow upward was found by Haines & Smith (1983) above a streamwise line source of buoyancy simulating a forest fire : their flow appears not to have been fully turbulent, and detailed comparisons with skew-induced vortices would not be useful.…”

Section: M M a Shabaka R U Mehta And P Bradshuwmentioning

confidence: 99%

Longitudinal vortices imbedded in turbulent boundary layers. Part 1. Single vortex

1985

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Detailed mean-flow and turbulence measurements have been made in a low-speed turbulent boundary layer in zero pressure gradient with an isolated, artificially generated vortex imbedded in it. The vortex was generated by a half-delta wing on the floor of the wind-tunnel settling chamber, so that the vortex entering the working section had the same circulation as that originally generated, while axial-component velocity variations were very much reduced, relative to the local mean velocity, from values just behind the generator. The measurements show that the circulation around the vortex imbedded in the boundary layer is almost conserved, being reduced only by the spanwise-component surface shear stress. Therefore the region of flow affected by the vortex continues to grow downstream, its cross-sectional dimensions being roughly proportional to the local boundary-layer thickness. The behaviour of the various components of eddy viscosity, deduced from measured Reynolds stresses, and of the various triple products, suggests that the simple empirical correlations for these quantities used in present-day turbulence models are not likely to yield flow predictions which are accurate in detail.

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“…1G and 2). These stream-wise vortices are not to be confused with shear-induced horizontal rotations at the outer edges of rising thermal plumes (33), which are elevated above the fuels. Instead, the vortex pairs described here force flames and hot gases downward and forward, splaying them horizontally within the fuel bed (Figs.…”

Section: Significancementioning

confidence: 99%

Role of buoyant flame dynamics in wildfire spread

Finney

Cohen

Forthofer

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

289

166

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Large wildfires of increasing frequency and severity threaten local populations and natural resources and contribute carbon emissions into the earth-climate system. Although wildfires have been researched and modeled for decades, no verifiable physical theory of spread is available to form the basis for the precise predictions needed to manage fires more effectively and reduce their environmental, economic, ecological, and climate impacts. Here, we report new experiments conducted at multiple scales that appear to reveal how wildfire spread derives from the tight coupling between flame dynamics induced by buoyancy and fine-particle response to convection. Convective cooling of the fine-sized fuel particles in wildland vegetation is observed to efficiently offset heating by thermal radiation until convective heating by contact with flames and hot gasses occurs. The structure and intermittency of flames that ignite fuel particles were found to correlate with instabilities induced by the strong buoyancy of the flame zone itself. Discovery that ignition in wildfires is critically dependent on nonsteady flame convection governed by buoyant and inertial interaction advances both theory and the physical basis for practical modeling.wildfires | buoyant instability | flame spread | convective heating

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Wind tunnel generation of horizontal roll vortices over a differentially heated surface

Cited by 22 publications

References 7 publications

Impact of fire behavior on postfire forest development in a homogeneous boreal landscape

Impact of fire behavior on postfire forest development in a homogeneous boreal landscape

Longitudinal vortices imbedded in turbulent boundary layers. Part 1. Single vortex

Role of buoyant flame dynamics in wildfire spread

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