Numerical investigation of flame–vortex interactions in laminar cross-flow non-premixed flames in the presence of bluff bodies
TL;DR: Shijin et al. as discussed by the authors investigated the regimes of flame stabilisation of non-premixed laminar flames established in a cross-flow combustor in the presence of a square cylinder.
Abstract: Flame stabilisation in a combustor having vortices generated by flame holding devices constitutes an interesting fundamental problem. The presence of vortices in many practical combustors ranging from industrial burners to high speed propulsion systems induces vortex–flame interactions and complex stabilisation conditions. The scenario becomes more complex if the flame sustains after separating itself from the flame holder. In a recent study [P.K. Shijin, S.S. Sundaram, V. Raghavan, and V. Babu, Numerical investigation of laminar cross-flow non-premixed flames in the presence of a bluff-body, Combust. Theory Model. 18, 2014, pp. 692–710], the authors reported details of the regimes of flame stabilisation of non-premixed laminar flames established in a cross-flow combustor in the presence of a square cylinder. In that, the separated flame has been shown to be three dimensional and highly unsteady. Such separated flames are investigated further in the present study. Flame–vortex interactions in sepa...
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TL;DR: In this paper, the stability of cross-flow non-premixed flames is studied systematically, where biogas is injected through a horizontal porous plate and air is blown parallel to the fuel injector.
12 citations
04 Jan 2018
TL;DR: In this paper, an unstructured grid finite volume method was used and simulations were carried out to simulate a two-dimensional laminar transient flow past a cylindrical bluff body.
Abstract: A two-dimensional, laminar transient flow past a cylindrical bluff body, with methane injection perpendicular to the direction of the free stream flow, i.e. the cross-flow arrangement, is numerically studied. An unstructured grid finite volume method is used and simulations were carried out. The methane mass fraction and the injection velocity of methane injected from the slotted cylinder are altered simultaneously, and their effects on the combustion, flame characteristics, and fluid mechanics are investigated. The flame is anchored right in front of the cylinder and is stabilized by the wake of the bluff body. The current investigation illustrates the qualitative aspects of the vortex shedding phenomena. A particular case of injection velocity and mass fraction is studied in detail and its vortex shedding phenomena are analysed minutely. The non-reacting flow exhibits 2P mode of vortex shedding while the reacting flow exhibits the more common 2S mode. Fast Fourier transform analysis of the temporally fluctuating lift coefficient is performed for the different cases carried out in the present study.
3 citations
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TL;DR: In this article, the authors propose a definition of vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor, which captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers.
Abstract: Considerable confusion surrounds the longstanding question of what constitutes a vortex, especially in a turbulent flow. This question, frequently misunderstood as academic, has recently acquired particular significance since coherent structures (CS) in turbulent flows are now commonly regarded as vortices. An objective definition of a vortex should permit the use of vortex dynamics concepts to educe CS, to explain formation and evolutionary dynamics of CS, to explore the role of CS in turbulence phenomena, and to develop viable turbulence models and control strategies for turbulence phenomena. We propose a definition of a vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor ${\bm {\cal S}}^2 + {\bm \Omega}^2$ are respectively the symmetric and antisymmetric parts of the velocity gradient tensor ${\bm \Delta}{\bm u}$. This definition captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers, unlike a pressure-minimum criterion. We compare our definition with prior schemes/definitions using exact and numerical solutions of the Euler and Navier–Stokes equations for a variety of laminar and turbulent flows. In contrast to definitions based on the positive second invariant of ${\bm \Delta}{\bm u}$ or the complex eigenvalues of ${\bm \Delta}{\bm u}$, our definition accurately identifies the vortex core in flows where the vortex geometry is intuitively clear.
5,837 citations
"Numerical investigation of flame–vo..." refers background in this paper
...The Q-criterion, suggested by Jeong and Hussain [29], identifies a vortex as the region with a positive value for the second invariant of the velocity gradient tensor....
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...Following Marble [7] and Alain and Candel [9], studies on diffusion flame–vortex interaction were carried out by Macaraeg, Jackson and Hussaini [12], using numerical simulations and asymptotic analysis....
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TL;DR: The equivalence of the matrices for processing, the objective functions, the optimal basis vectors, the mean-square errors, and the asymptotic connections of the three POD methods are demonstrated and proved when the methods are used to handle the POD of discrete random vectors.
682 citations
Book•
01 May 1993
TL;DR: In this article, an introduction to the up-to-date technology used in reducing kinetic mechanisms especially for combustion systems is presented, as well as the most recent methods for modelling a variety of systems.
Abstract: This book is an introduction to the up-to-date technology used in reducing kinetic mechanisms especially for combustion systems. However, it can also be used as a handbook, in that it presents the most recent methods for modelling a variety of systems. In addition it presents existing software for reducing mechanisms and flame calcualtions for mixed and pre-mixed flames and fuels ranging from hydrogen to propane, and it defines a format for general flamelet libraries. Details are thoroughly compared with experimental data. This volume addresses scientists, graduate students and chemical engineers in industry and environmental research.
577 citations
"Numerical investigation of flame–vo..." refers background in this paper
...A C1 mechanism [25] with 18 species and 43 reaction steps is selected for the present study after comparing the predictions of different mechanisms and establishing the adequacy of the C1 mechanism [24]....
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TL;DR: In this article, the authors used Raman scattering and laser-induced fluorescence to measure temperature, the major species (N2, O2, CH4, CO2, H2O, CO, and H2), OH, and NO in steady laminar opposed-flow partially premixed flames of methane and air.
495 citations
"Numerical investigation of flame–vo..." refers methods in this paper
...A radiation sub-model based on the optically thin approximation [26] is used to account for the thermal radiation absorbed by the CH4, CO2, H2O and CO species....
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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