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Flow field of a diffusion flame attached to a thick-walled injector between two coflowing reactant streams

Published online by Cambridge University Press:  26 April 2006

F. J. Higuera  and
A. Liñán
F. J. Higuera
Affiliation:
ETS Ingenieros Aeronáuticos, Pza. Cardenal Cisneros 3, 28040 Madrid, Spain
A. Liñán
Affiliation:
ETS Ingenieros Aeronáuticos, Pza. Cardenal Cisneros 3, 28040 Madrid, Spain
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Abstract

The flow field of a diffusion flame attached to a thick-rim injector between two coflowing streams of fuel and oxidiser is analysed in the Burke–Schumann limit of infinitely fast reaction rate. The length of the recirculation region immediately behind the injector and the velocity of the recirculating fluid are proportional to the shear stresses of the reactant streams on the wall of the injector for a range of rim thicknesses, and the structure of the flow in the wake depends then on three main non-dimensional parameters, measuring the gas thermal expansion due to the chemical heat release, the air-to-fuel stoichiometric ratio of the reaction, and the air-to-fuel ratio of wall shear stresses. The recirculation region shortens with increasing heat release, and the position of the flame in this region depends on the other two parameters. An asymptotic analysis is carried out for very exothermic reactions, showing that the region of high temperature around the flame is confined by neatly defined boundaries and the hot fluid moves like a high-velocity jet under a favourable self-induced pressure gradient. The immediate wake is surrounded by a triple-deck region where the interacting flow leads to an adverse pressure gradient and a reduced shear stress upstream of the injector rim for sufficiently exothermic reactions. Separation of the boundary layers on the wall of the injector, however, seems to be postponed to very large values of the gas thermal expansion.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 329 , 25 December 1996 , pp. 389 - 411
Copyright
© 1996 Cambridge University Press

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