Optical Transfer Function Measurements for Technically Premixed Flames

Schuermans, Bruno; Guethe, Felix; Mohr, Wolfgang F. D.

doi:10.1115/1.3124663

Cited by 18 publications

(9 citation statements)

References 16 publications

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“…4,5 When optical access is possible, this response is generally characterized experimentally by determining flame transfer functions (FTFs) or, more recently, flame describing functions relating heat release rate disturbances to flow rate or mixture composition oscillations produced at some location in the injector for different flow and excitation conditions. [6][7][8][9][10][11][12] These characterizations have proven valuable for linear and nonlinear stability analyses of the system dynamics; in addition, they are used to determine stability charts as the operating conditions of the combustor are modified. 5, [13][14][15][16][17] With the rapid development of high-performance computing resources, it is nowadays also possible to capture the response of flames to flow disturbances in complex combustor geometries by solving the compressible Navier-Stokes equations in multi-species reacting flows using Large-Eddy Simulation (LES) tools.…”

Section: Introductionmentioning

confidence: 99%

Response analysis of a laminar premixed M-flame to flow perturbations using a linearized compressible Navier-Stokes solver

Blanchard

Schuller

Sipp³

et al. 2015

Physics of Fluids

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International audienceThe response of a laminar premixed methane-air flame subjected to flow perturbations around a steady state is examined experimentally and using a linearized compressible Navier-Stokes solver with a one-step chemistry mechanism to describe combustion. The unperturbed flame takes an M-shape stabilized both by a central bluff body and by the external rim of a cylindrical nozzle. This base flow is computed by a nonlinear direct simulation of the steady reacting flow, and the flame topology is shown to qualitatively correspond to experiments conducted under comparable conditions. The flame is then subjected to acoustic disturbances produced at different locations in the numerical domain, and its response is examined using the linearized solver. This linear numerical model then allows the componentwise investigation of the effects of flow disturbances on unsteady combustion and the feedback from the flame on the unsteady flow field. It is shown that a wrinkled reaction layer produces hydrodynamic disturbances in the fresh reactant flow field that superimpose on the acoustic field. This phenomenon, observed in several experiments, is fully interpreted here. The additional perturbations convected by the mean flow stem from the feedback of the perturbed flame sheet dynamics onto the flow field by a mechanism similar to that of a perturbed vortex sheet. The different regimes where this mechanism prevails are investigated by examining the phase and group velocities of flow disturbances along an axis oriented along the main direction of the flow in the fresh reactant flow field. It is shown that this mechanism dominates the low-frequency response of the wrinkled shape taken by the flame and, in particular, that it fully determines the dynamics of the flame tip from where the bulk of noise is radiated

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Section: Introductionmentioning

confidence: 99%

Response analysis of a laminar premixed M-flame to flow perturbations using a linearized compressible Navier-Stokes solver

Blanchard

Schuller

Sipp³

et al. 2015

Physics of Fluids

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“…The chemiluminescence emission has been assumed to be proportional to the total heat-release rate [9,22,23] . At each test point, the pressure and PMT data are sampled at a frequency of 8192 Hz for 4 s on a data acquisition system (National Instruments, BNC-2111), resulting in a spectral resolution of 0.25 Hz and a temporal resolution of 0.122 ms. All of the experiments are performed at ambient temperature ( T a = 293 K) and atmospheric pressure.…”

Section: Methodsmentioning

confidence: 99%

Extracting flame describing functions in the presence of self-excited thermoacoustic oscillations

Balusamy

Han

et al. 2017

Proceedings of the Combustion Institute

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One of the key elements in the prediction of thermoacoustic oscillations is the determination of the acoustic response of flames as an element in an acoustic network, in the form of a flame describing function (FDF). In order to obtain a response, flames often have to be confined into a system with its own acoustic response. Separating the pure flame response and that of the system can be complicated by the non-linear effects that the flame can have on the overall system response. In this paper, we investigate whether it is possible to obtain a flame response via the usual methods of dynamic chemiluminescence and pressure measurements, starting from an unforced system with incipient self-excitations at a given frequency f s , in the form of a stabilized flame at atmospheric pressure with a 700 mm tube as a combustor. The flame is forced at discrete frequencies from 20 to 400 Hz, away from the self-excitation, and the response of the flame is measured using OH * chemiluminescence. This response was compared to a flame response measured in a short tube with no other excitations.The results show that both the gain and phase can be entirely dominated by the behavior of the self-excitation, so that in general it is not possible to extract reliable gain and phase information as if the forced and selfexcited modes acted independently and linearly. Although the gain in this particular case was not significantly affected, the phase information of the original flame became dominated by the triggered self-excitation.Boundary conditions and systems used for flame acoustic forcing therefore need to be carefully controlled whenever there is a possibility of self-excitation.

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“…Light emission measurement of CH Ã or OH Ã radicals is a well established technique [4,5], which works well in perfectly premixed flames. However, the emission may depend on local equivalence ratio [6][7][8][9], turbulence intensity [9,10], flame front properties [11], and temperature and pressure [12][13][14][15]. As a consequence, for obtaining quantitative information of the heat release rates, the signals have to be calibrated in subsequent steps (see for instance [9,16,17] for different strategies).…”

Section: Introductionmentioning

confidence: 99%