Boundary layer instabilities in mixed convection and diffusion flames with an unheated starting length

Miller, Colin H.; Tang, Wei; Sluder, Evan; Finney, Mark A.; McAllister, Sara; Forthofer, Jason; Gollner, Michael J.

doi:10.1016/j.ijheatmasstransfer.2017.11.040

Cited by 16 publications

(4 citation statements)

References 40 publications

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“…Moreover, the tower trough structures are persistently present even in well-developed fires, not only in transition flows. Other authors have found similar results on inclined plates [13,24], and some researchers have noted that the counter-rotational vortices have some similarities to Görtler vortices [2,[8][9][10][19][20][21]. It is important to note that the tower and trough pattern is similar but not identical to Görtler vortices, which arise as a result of fluid impinging upon a curved surface (i.e., Görtler vortices are a combination of forward momentum and centrifugal force, while the heated plate towers and troughs arise from forward momentum and the force due to buoyancy) [25][26][27].…”

Section: Introductionmentioning

confidence: 59%

“…The observation of towers and trough-like structures associated with strong buoyancy driven environments can be traced back to several studies involving heated plates [4][5][6][7]. Stationary diffusion flames have also been used in efforts to study the interactions between forward momentum and buoyancy without the additional complexities of combustion [8][9][10]. Boundary layer instabilities could develop into counter-rotating streamwise vortices which were associated with the visible tower and trough pattern in wind-driven fire scenarios.…”

Section: Introductionmentioning

confidence: 99%

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Identifying Characteristics of Wildfire Towers and Troughs

et al. 2020

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Wildfire behavior is dictated by the complex interaction of numerous physical phenomena including dynamic ambient and fire-induced winds, heat transfer, aerodynamic drag on the wind by the fuel and combustion. These phenomena create complex feedback effects between the fire and its surroundings. In this study, we aim to study the mechanisms by which buoyant flame dynamics along with vortical motions and instabilities control wildfire propagation. Specifically, this study employs a suite of simulations conducted with the physics-based coupled fire-atmosphere behavior model (FIRETEC). The simulations are initialized with a fire line and the fires are allowed to propagate on a grass bed, where the fuel heights and wind conditions are varied systematically. Flow variables are extracted to identify the characteristics of the alternating counter-rotational vortices, called towers and troughs, that drive convective heat transfer and fire spread. These vortices have previously been observed in wildfires and laboratory fires, and have also been observed to arise spontaneously in FIRETEC due to the fundamental physics incorporated in the model. However, these past observations have been qualitative in nature and no quantitative studies can be found in the literature which connected these coherent structures fundamental to fire behavior with the constitutive flow variables. To that end, a variety of state variables are examined in the context of these coherent structures under various wind profile and grass height conditions. Identification of various correlated signatures and fire-atmosphere feedbacks in simulations provides a hypothesis that can be tested in future observational or experimental efforts, potentially assisting experimental design, and can aid in the interpretation of data from in situ detectors.

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Section: Introductionmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Identifying Characteristics of Wildfire Towers and Troughs

et al. 2020

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“…The flame length was also found to be related to the nondimensional fire size, however no correlations were found to adequately scale inclined flames. These results were scaled and included with larger scale studies in (Finney et al 2015) Further study of instabilities observed in flames was carried out by Miller et al 2018). In a small-scale line burner was used in crossflow to track the growth and development of a laminar streak entering a flame.…”

mentioning

confidence: 99%

“…However, the growth of these structures was eventually dominated by a Rayleigh-Taylor instability. In Miller et al ( , 2018 this work was extended using hot plates and a liquid wick to track the merging and growth of flow structures. It appeared that these initial streaks grow into larger-scale structures (peaks and troughs) which then dominate some forward flame motions.…”

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confidence: 99%

Understanding the dynamics of inclined and wind-driven flames in wildland fires

Gollner¹,

Tang²,

Finney³

et al.

Advances in Forest Fire Research 2018

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A navegação consulta e descarregamento dos títulos inseridos nas Bibliotecas Digitais UC Digitalis, UC Pombalina e UC Impactum, pressupõem a aceitação plena e sem reservas dos Termos e Condições de Uso destas Bibliotecas Digitais, disponíveis em https://digitalis.uc.pt/pt-pt/termos. Conforme exposto nos referidos Termos e Condições de Uso, o descarregamento de títulos de acesso restrito requer uma licença válida de autorização devendo o utilizador aceder ao(s) documento(s) a partir de um endereço de IP da instituição detentora da supramencionada licença. Ao utilizador é apenas permitido o descarregamento para uso pessoal, pelo que o emprego do(s) título(s) descarregado(s) para outro fim, designadamente comercial, carece de autorização do respetivo autor ou editor da obra. Na medida em que todas as obras da UC Digitalis se encontram protegidas pelo Código do Direito de Autor e Direitos Conexos e demais legislação aplicável, toda a cópia, parcial ou total, deste documento, nos casos em que é legalmente admitida, deverá conter ou fazer-se acompanhar por este aviso. Understanding the dynamics of inclined and wind-driven flames in wildland fires Autor(es): Gollner, M. J.; Tang, W.; Miller, C. H.; McAllister, S.; Finney, M. A. Publicado por: Imprensa da Universidade de Coimbra URL persistente: URI:http://hdl.handle.net/10316.2/44593Abstract Time-dependent movements described as pulsing, puffing or swaying are among the most visible characteristics of open flames. Most existing models for wildfires, however, have assumed flames are motionless and spread at a constant rate via radiation, neglecting any clearly intermittent behaviour. Recent studies of spreading wildfires suggest that flame spread in fine fuel beds is driven by non-steady convective heating and intermittent flame contact on fuel particles. To further understand the impact and nature of these flame motions, a stationary, non-spreading fire configuration has been used as it allows for a thorough statistical analysis of the flame structure. The same intermittent heating observed in the fuel bed experiments were observed in the stationary burner, but with the ability to collect a larger data set. Scaling analyses which investigate the impact of these structures, theories on their generation and their impact to fire spread will be discussed for both wind-driven and slope-dominated flames.

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