Stretch-induced quenching in flame-vortex interactions
01 Dec 1993-
TL;DR: In this paper, the interaction of an isolated vortex with a laminar premixed flame is viewed as a unit process of a turbulent pre-mixing flame in which the reaction zone keeps a lamination-like structure locally; this is the case of the wrinkled flame or flamelet regime in turbulent combustion.
Abstract: The flame-vortex interaction problem is a natural configuration in which several issues relevant to turbulent combustion can be addressed: effect of strain-rate and curvature, effect of the Lewis number, effect of heat losses, effect of complex chemistry, and flame-generated turbulence. In such an approach, the interaction of an isolated vortex with a laminar premixed flame is viewed as a unit process of a turbulent premixed flame in which the reaction zone keeps a laminar like structure locally; this is precisely the case of the wrinkled flame or flamelet regime in turbulent combustion. The present work complements previous studies and involves the study of the interaction of a vortex pair and a laminar premixed flame in a planar two-dimensional geometry, together with numerical simulations. This geometry is quite unique since most studies have considered axisymmetric vortex rings. Such a geometry offers several advantages over previous studies.
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TL;DR: A review of flame/vortex interactions with flames can be found in this article, where progress in theoretical, numerical, and experimental investigations on flame/Vortex interactions is reviewed.
290 citations
TL;DR: In this article, the local structure of flamelets in premixed turbulent combustion is investigated using two and three-dimensional direct numerical simulations with simple chemistry models and effects of complex chemistry are considered through recent two-dimensional DNS performed with realistic chemical schemes.
230 citations
TL;DR: In this paper, a stiff,^1 operator-split projection scheme is constructed for the simulation of unsteady two-dimensional reacting flow with detailed kinetics, based on the compressible conservation equations for an ideal gas mixture in the zero-Mach-number limit.
148 citations
TL;DR: In this article, a compilation of results from numerical computations of the interaction of a premixed methane flame with a two-dimensional counter-rotating vortex pair using detailed kinetics is presented.
Abstract: The use of particular experimental flame observables as flame markers, and as measures of flame burning and heal release rates requires the establishment of robust correlations between the particular observable and the rate in question. In this work, we use a compilation of results from numerical computations of the interaction of a premixed methane flame with a two-dimensional counter-rotating vortex pair using detailed kinetics. The data set involves the use of two different chemical mechanisms, a two-fold variation in flow time scales, and the examination of both stoichiometric and rich methane flames. Correlations between a number of flame observables and heat release and burning rates are examined. We study HCO, ▽·v, OH, CH, CO, CH3, CH2O, CH2*, and C2H2, as well as various concentration products (surrogates for production rates) including [OH][CH2O], [OH][CH4], and [OH][CO]. Other concentration products expected to relate to chemiluminescent observables such as CH*, OH* and CO2*, are also studied. H...
127 citations
01 Dec 1994
TL;DR: In this article, the authors studied the stabilization of diffusion flames using asymptotic techniques and numerical tools and showed that stabilization of a diffusion flame may only occur behind the flame holder in the wake of the splitter plate.
Abstract: The stabilization of diffusion flames is studied using asymptotic techniques and numerical tools. The configuration studied corresponds to parallel streams of cold oxidizer and fuel initially separated by a splitter plate. It is shown that stabilization of a diffusion flame may only occur in this situation by two processes. First, the flame may be stabilized behind the flame holder in the wake of the splitter plate. For this case, numerical simulations confirm scalings previously predicted by asymptotic analysis. Second, the flame may be lifted. In this case a triple flame is found at longer distances downstream of the flame holder. The structure and propagation speed of this flame are studied by using an actively controlled numerical technique in which the triple flame is tracked in its own reference frame. It is then possible to investigate the triple flame structure and velocity. It is shown, as suggested from asymptotic analysis, that heat release may induce displacement speeds of the triple flame larger than the laminar flame speed corresponding to the stoichiometric conditions prevailing in the mixture approaching the triple flame. In addition to studying the characteristics of triple flames in a uniform flow, their resistance to turbulence is investigated by subjecting triple flames to different vortical configurations.
46 citations
Cites methods from "Stretch-induced quenching in flame-..."
...The influence of turbulence is investigated later in Section 6 by using a technique developed previously for premixed flames both experimentally and numerically (Roberts et ai 1993, Samaniego 1993, Poinsot et al. 1991): vórtices are generated upstream of the fíame and interact with the ñame front....
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References
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TL;DR: In this article, a review of recent developments in flame theory is provided, in sufficient detail to give the reader a comprehensive introduction to the field, including the stability and flammability limits of planar fronts, cellular flames, flame stretch, turbulent and self-turbulizing flames, hydrodynamic interactions between weakly turbulent gas flows and wrinkled flame fronts, molecular diffusion effects of intermediate species involved in chain reactions.
912 citations
TL;DR: A review of the current state of the art in turbulent combustion modelling can be found in this article, where the authors present physical and experimental knowledge of the structure of turbulent flames in order to help the further discussions of models on a physical basis.
572 citations
TL;DR: In this article, the authors investigated low-frequency vortex-driven combustion instability in the case of a multiple inlet combustor with dump and showed that lowfrequency instabilities are acoustically coupled and occur at the eigenfrequencies of the system.
Abstract: Combustion instability is investigated in the case of a multiple inlet combustor with dump. It is shown that low-frequency instabilities are acoustically coupled and occur at the eigenfrequencies of the system. Using spark-schlieren and a special phase-average imaging of the C 2 -radical emission, the fluid-mechanical processes involved in a vortex-driven mode of instability are investigated. The phase-average images provide maps of the local non-steady heat release. From the data collected on the combustor the processes of vortex shedding, growth, interactions and burning are described. The phases between the pressure, velocity and heat-release fluctuations are determined. The implications of the global Rayleigh criterion are verified and a mechanism for low-frequency vortex-driven instabilities is proposed.
562 citations
TL;DR: In this paper, an extended definition of flamelet regimes based on the existence of a continuous active (not quenched) flame front separating fresh gases and burnt products is introduced.
Abstract: The structure of premixed turbulent flames is a problem of fundamental interest in combustion theory. Possible flame geometries have been imagined and diagrams indicating the corresponding regimes of combustion have been constructed on the basis of essentially intuitive and dimensional considerations. A new approach to this problem is described in the present paper. An extended definition of flamelet regimes based on the existence of a continuous active (not quenched) flame front separating fresh gases and burnt products is first introduced. Direct numerical simulations of flame/vortex interactions using the full Navier–Stokes equations and a simplified chemistry model are then performed to predict flame quenching by isolated vortices. The formulation includes non-unity Lewis number, non-constant viscosity and heat losses so that the effect of stretch, curvature, transient dynamics and viscous dissipation can be accounted for. As a result, flame quenching by vortices (which is one of the key processes in premixed turbulent combustion) may be computed accurately. The effects of curvature and viscous dissipation on flame/vortex interactions may also be characterized by the same simulations. The influence of non-unity Lewis number and of thermo-diffusive processes in turbulent premixed combustion is discussed by comparing flame responses for two values of the Lewis number (Le = 0.8 and 1.2). An elementary (‘spectral’) diagram giving the response of one flame to a vortex pair is constructed. This spectral diagram is then used, along with certain assumptions, to establish a turbulent combustion diagram similar to those proposed by Borghi (1985) or Williams (1985). Results show that flame fronts are much more resistant to quenching by vortices than expected from the classical theories. A cut-off scale and a quenching scale are also obtained and compared with the characteristic scales proposed by Peters (1986). Results show that strain is not the only important parameters determining flame/vortex interaction. Heat losses, curvature, viscous dissipation and transient dynamics have significant effects, especially for small scales and they strongly influence the boundaries of the combustion regimes. It is found, for example, that the Klimov–Williams criterion which is generally advocated to limit the flamelet region, underestimates the size of this region by more than an order of magnitude.
416 citations
01 Jan 1988
TL;DR: In this paper, a review of recent advances in the understanding of the structure, propagation, and extinction of laminar flames under the influence of stretch, as manifested by the existence of flame curvature, flow nonuniformity, and flame motion, is reviewed.
Abstract: Recent advances in the understanding of the structure, propagation, and extinction of laminar flames under the influence of stretch, as manifested by the existence of flame curvature, flow nonuniformity, and flame motion, are reviewed. The emphasis is on premixed flames because of the richness and subtlety of the phenomena involved. The review distinguishes the influences of the tangential and normal velocity gradients on the flame response, both at the hydrodynamic scale and within the flame structure, and emphasizes the importance of the preferential diffusion nature of heat and mass transport, as well as the extent to which the flame can freely adjust its location in response to stretch in order to achieve complete reaction. It is then demonstrated that stretch has only minimal effect on an adiabatic, unrestrained, diffusionally-neutral flame with complete reaction in that the temperature, propagation rate, and thickness of the flame are invariant to stretch, and that stretch alone cannot extinguish such a flame. In the presence of preferential diffusion and/or when the flame movement is restrained, the response of the flame to stretch becomes more sensitive and extinction is also possible. The concept of flame stretch is applied to interpret such practical flame phenomena as flame stabilization and flame-front instability, determination of laminar flame speeds and flammability limits, concentration and temperature modifications in flame chemistry, and modeling of turbulent flames. The properties of stretched diffusion flames are then briefly discussed. The review closes with suggestions for further research.
387 citations