@MastersThesis{Severino:2020:CoReTs,
author = "Severino, Matheus de P{\'a}dua",
title = "Diffusion flames with continuous change in properties: from
counterflow regime (Tsuji flame) to coflow regime (Burke-Schumann
flame)",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2020",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2020-02-28",
keywords = "double Tsuji diffusion flame, cylindrical burner in impinging
flows, transition from transient to stationary regime, asymptotic
analysis, characteristic scales.",
abstract = "Understanding any phenomenon at the most fundamental level is
essential for the later comprehension of more complex phenomena,
because they are nothing more than a set of elementary phenomena,
influencing each other. Diffusion flame established around a
cylindrical burner is inherently two-dimensional. Tsuji and his
partners worked for more than 20 years on cylindrical burners.
Theirs experiments aimed, notably, to determine the influence of
the strain rate on the flame stability. Recently, Tsuji flame has
received more attention, but examining the entire flame and not
only the region near the point of stagnation, under forced and
natural convection. The present work endeavors to analyze a
similar problem but considering a cylindrical burner in impinging
flows. The objective is to determine the influence of burner, flow
field and stoichiometry on the flame, developing and implementing
numerically a mathematical model and determining analytical
solutions. Making the model simple and without loss of generality,
potential flow is assumed. According to the hypotheses considered,
the mixture fraction and the excess of enthalpy describe the
evolution of fuel mass fraction, oxidant mass fraction and
temperature. The flame spends most of its lifetime in a region of
the flow field scaled with the reciprocal of square root of strain
rate and velocities are scaled with the square root of strain
rate. The results demonstrate that the initial flame displacement
is controlled by radial transport of fuel into the region nearby
the burner, in which the impinging flows have a negligible
influence. After that period, the flame is strongly influenced by
the impinging flows, when its acceleration is observed. The flame
length is proportional to the stoichiometric coefficient, ejecting
velocity and reciprocal to square root of strain rate. Meanwhile,
the flame width is only dependent on the reciprocal of square root
of strain rate. Moreover, the proposed asymptotic solution
underlines the most significant transport mechanisms for the flame
in different conditions and allows the deduction of important
properties such as stagnation points, strain rate, approximate
solutions and gradients. RESUMO: A compreens{\~a}o de qualquer
fen{\^o}meno no n{\'{\i}}vel mais fundamental {\'e} essencial
para o entendimento posterior de fen{\^o}menos mais complexos,
pois eles n{\~a}o passam de um conjunto de fen{\^o}menos
elementares, influenciando-se mutuamente. A chama difusiva
estabelecida em torno de um queimador cil{\'{\i}}ndrico {\'e}
inerentemente bidimensional. Tsuji e parceiros trabalharam por
mais de 20 anos em queimadores cil{\'{\i}}ndricos. Eles
objetivaram, nomeadamente, determinar a influ{\^e}ncia da taxa de
estiramento na estabilidade da chama. Recentemente, a chama Tsuji
voltou {\`a} an{\'a}lise, examinando-se toda a chama e n{\~a}o
apenas a regi{\~a}o pr{\'o}xima ao ponto de
estagna{\c{c}}{\~a}o, sob convec{\c{c}}{\~a}o for{\c{c}}ada e
natural. O presente trabalho procura analisar um problema
semelhante, mas considerando um queimador cil{\'{\i}}ndrico em
escoamentos impingentes. O objetivo {\'e} determinar a
influ{\^e}ncia do queimador, escoamento e estequiometria na
chama, desenvolvendo e implementando numericamente um modelo
matem{\'a}tico e determinando solu{\c{c}}{\~o}es
anal{\'{\i}}ticas. Por simplifidade e sem perda de generalidade,
assume-se um escoamento potencial. De acordo com as hip{\'o}teses
consideradas, a fra{\c{c}}{\~a}o de mistura e o excesso de
entalpia descrevem a evolu{\c{c}}{\~a}o da fra{\c{c}}{\~a}o de
massa do combust{\'{\i}}vel, fra{\c{c}}{\~a}o de massa do
oxidante e temperatura. A chama passa a maior parte do tempo em
uma regi{\~a}o do escoamento escalonada com a rec{\'{\i}}proca
da raiz quadrada da taxa de estiramento e as velocidades s{\~a}o
escalonadas com a raiz quadrada da taxa de estiramento. Os
resultados demonstram que o deslocamento inicial da chama {\'e}
controlado pelo transporte radial do combust{\'{\i}}vel para a
regi{\~a}o pr{\'o}xima ao queimador, na qual os escoamentos
impingentes t{\^e}m uma influ{\^e}ncia insignificante. Ap{\'o}s
esse per{\'{\i}}odo, a chama {\'e} fortemente influenciada
pelos escoamentos impingentes, quando a sua acelera{\c{c}}{\~a}o
{\'e} observada. O comprimento da chama {\'e} proporcional ao
coeficiente estequiom{\'e}trico, {\`a} velocidade de
eje{\c{c}}{\~a}o e {\`a} rec{\'{\i}}proca da raiz quadrada da
taxa de estiramento. Entretanto, a largura da chama depende apenas
da rec{\'{\i}}proca da raiz quadrada da taxa de estiramento.
Al{\'e}m disso, a solu{\c{c}}{\~a}o assint{\'o}tica proposta
destaca os mecanismos de transporte mais significativos para a
chama em diferentes condi{\c{c}}{\~o}es e permite a
dedu{\c{c}}{\~a}o de propriedades importantes, como pontos de
estagna{\c{c}}{\~a}o, taxa de estiramento, solu{\c{c}}{\~o}es
aproximadas e gradientes.",
committee = "Fachini Filho, Fernando (presidente/orientador) and
Mendon{\c{c}}a, M{\'a}rcio Teixeira de and Dourado, Wladimyr
Mattos da Costa and Sauer, Vin{\'{\i}}cius Maron",
englishtitle = "Chamas difusivas com mudan{\c{c}}a cont{\'{\i}}nua nas
propriedades: do regime de contrafluxo (chama de Tsuji) ao regime
de co-fluxo (chama de Burke-Schumann)",
language = "en",
pages = "89",
ibi = "8JMKD3MGP3W34R/3UTT928",
url = "http://urlib.net/ibi/8JMKD3MGP3W34R/3UTT928",
targetfile = "publicacao.pdf",
urlaccessdate = "27 abr. 2024"
}