Wrinkling, pocket formation, and double premixed flame interaction processes
01 Jan 1998-Vol. 27, Iss: 1, pp 659-666
TL;DR: In this paper, an experimental method was used to analyze some fundamental features of a double laminar premixed flame interacting with a single vortex ring, and a steady double premixed counterflow flame of propane and air was first established between two opposed nozzles.
Abstract: An experimental method of investigation is used to analyze some fundamental features of a double laminar premixed flame interacting with a single vortex ring. A steady double premixed counterflow flame of propane and air is first established between two opposed nozzles. A vortex ring is generated from a cylindrical tube installed in the lower combustor nozzle and impinges on one flame if the vortex is weak and on both flames if not. The interaction between the toroidal vortex and the lower flame provides complementary information on the fundamental interaction processes previously studied by Driscoll and coworkers. Comparisons with the numerical simulations of Poinsot et al, are made and confirm the theoretical predictions. The interaction between the vortex and the upper reactive layer is alos interesting as it gives information on the dynamics of two colliding premixed flames and can be used to investigate flamefront mutal interaction processes. The ability of the vortex to reach the second flame front is characterized by a new number Tt(r) , and flame merging processes are discussed.
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TL;DR: In this paper, the effects of molecular transport on turbulent flame propagation and structure are critically discussed and the results of relevant studies of perturbed laminar flames (unstable flames, flame balls, flames in vortex tubes) are reviewed.
305 citations
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 paper, a new experimental method is described that provides high-speed movies of turbulent premixed flame wrinkling dynamics and the associated vorticity fields, which has been applied to a turbulent slot Bunsen flame.
Abstract: A new experimental method is described that provides high-speed movies of turbulent premixed flame wrinkling dynamics and the associated vorticity fields. This method employs cinema stereoscopic particle image velocimetry and has been applied to a turbulent slot Bunsen flame. Three-component velocity fields were measured with high temporal and spatial resolutions of 0.9 ms and 140 μm, respectively. The flame-front location was determined using a new multi-step method based on particle image gradients, which is described. Comparisons are made between flame fronts found with this method and simultaneous CH-PLIF images. These show that the flame contour determined corresponds well to the true location of maximum gas density gradient. Time histories of typical eddy–flame interactions are reported and several important phenomena identified. Outwardly rotating eddy pairs wrinkle the flame and are attenuated at they pass through the flamelet. Significant flame-generated vorticity is produced downstream of the wrinkled tip. Similar wrinkles are caused by larger groups of outwardly rotating eddies. Inwardly rotating pairs cause significant convex wrinkles that grow as the flame propagates. These wrinkles encounter other eddies that alter their behavior. The effects of the hydrodynamic and diffusive instabilities are observed and found to be significant contributors to the formation and propagation of wrinkles.
100 citations
Cites background from "Wrinkling, pocket formation, and do..."
...Common configurations for premixed flame experiments include planar wake generated vortices impinging on a V-flame (Lee et al. 1993, 1995; Nye et al. 1996; Hargrave and Jarvis 2006), and interactions between a 2D outwardly rotating vortex pair and a laminar flat flame (Roberts and Driscoll 1991; Mueller et al. 1998; Sinibaldi et al. 1998) or counterflow flame ( Renard et al. 1998 )....
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TL;DR: In this article, a joint numerical and experimental study of unsteady premixed flame propagation around three sequential obstacles in a small-scale vented explosion chamber is presented, where the modeling work is carried out utilizing large eddy simulation (LES).
Abstract: In gas explosions, the unsteady coupling of the propagating flame and the flow field induced by the presence of blockages along the flame path produces vortices of different scales ahead of the flame front. The resulting flame–vortex interaction intensifies the rate of flame propagation and the pressure rise. In this paper, a joint numerical and experimental study of unsteady premixed flame propagation around three sequential obstacles in a small-scale vented explosion chamber is presented. The modeling work is carried out utilizing large eddy simulation (LES). In the experimental work, previous results (Patel et al., Proc Combust Inst 29:1849–1854, 2002) are extended to include simultaneous flame and particle image velocimetry (PIV) measurements of the flow field within the wake of each obstacle. Comparisons between LES predictions and experimental data show a satisfactory agreement in terms of shape of the propagating flame, flame arrival times, spatial profile of the flame speed, pressure time history, and velocity vector fields. Computations through the validated model are also performed to evaluate the effects of both large-scale and sub-grid scale (SGS) vortices on the flame propagation. The results obtained demonstrate that the large vortical structures dictate the evolution of the flame in qualitative terms (shape and structure of the flame, succession of the combustion regimes along the path, acceleration-deceleration step around each obstacle, and pressure time trend). Conversely, the SGS vortices do not affect the qualitative trends. However, it is essential to model their effects on the combustion rate to achieve quantitative predictions for the flame speed and the pressure peak.
98 citations
Cites background from "Wrinkling, pocket formation, and do..."
...[46] and Samaniego and Mantel [47] have complemented the...
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TL;DR: In this paper, the effect of the grid resolution on the impact of the combustion sub-model was investigated, and it was found that the amount of detail explicitly resolved on the finer grid (with a resolution of the same order of magnitude as the laminar flame thickness) is such that, even without the combustion subsumption, the LES results obtained with this grid correctly match the experimental data in both quantitative (flame speed and flow velocity) and qualitative (shape and structure of the flame front) terms.
64 citations
References
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TL;DR: In this article, the mechanisms and rate parameters for the gas-phase reactions of nitrogen compounds that are applicable to combustion-generated air pollution are discussed and illustrated by comparison of results from detailed kinetics calculations with experimental data.
2,843 citations
TL;DR: In this paper, an asymptotic nonlinear integrodifferential equation for spontaneous instability of the plane front of a laminar flame is derived, and it is shown that in all cases spontaneous instability implies an increase in its propagation velocity.
1,265 citations
TL;DR: In this article, the laminar flame speeds of methane + air and propane + air mixtures, with and without the addition of stoichiometrically small amounts of hydrogen, have been determined by first measuring the flame speeds with stretch and then linearly extrapolating these values to zero stretch.
508 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
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