Numerical study on intrinsic thermoacoustic instability of a laminar premixed flame

Silva, Camilo F.; Emmert, Thomas; Jaensch, S.; Polifke, Wolfgang

doi:10.1016/j.combustflame.2015.06.003

Cited by 68 publications

(54 citation statements)

References 36 publications

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“…wherec =c/c re f such thatc 2 = γp/ρ. The Laplace transform 13 of Eqn. (21) is the Helmholtz equation 14…”

Section: Helmholtz Equationmentioning

confidence: 99%

“…• the flow is one-dimensional, i.e., the characteristic acoustic frequency,f ac , is smaller than the cut-off frequency; • the flame is compact, i.e., the flame Helmholtz number, He ≡ 2πf acL /c, and the flame Strouhal number, St ≡ 2πf ac ,L/ũ are negligible [198], whereL is the axial spatial extent of the flame; 13 For a generic function f, the Laplace transform is defined as L{f} ≡ 14 Technically, this is an inhomogeneous Helmholtz equation, however, the adjective inhomogeneous is dropped for brevity.…”

Section: Helmholtz Equationmentioning

confidence: 99%

“…Additionally, there exist thermoacoustic instabilities that occur in anechoic systems, which are called intrinsic thermoacoustic instabilities[9][10][11][12][13][14][15] 2. i.e.…”

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confidence: 99%

See 2 more Smart Citations

Adjoint Methods as Design Tools in Thermoacoustics

Magri

2019

Applied Mechanics Reviews

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In a thermoacoustic system, such as a flame in a combustor, heat release oscillations couple with acoustic pressure oscillations. If the heat release is sufficiently in phase with the pressure, these oscillations can grow, sometimes with catastrophic consequences. Thermoacoustic instabilities are still one of the most challenging problems faced by gas turbine and rocket motor manufacturers. Thermoacoustic systems are characterized by many parameters to which the stability may be extremely sensitive. However, often only few oscillation modes are unstable. Existing techniques examine how a change in one parameter affects all (calculated) oscillation modes, whether unstable or not. Adjoint techniques turn this around: They accurately and cheaply compute how each oscillation mode is affected by changes in all parameters. In a system with a million parameters, they calculate gradients a million times faster than finite difference methods. This review paper provides: (i) the methodology and theory of stability and adjoint analysis in thermoacoustics, which is characterized by degenerate and nondegenerate nonlinear eigenvalue problems; (ii) physical insight in the thermoacoustic spectrum, and its exceptional points; (iii) practical applications of adjoint sensitivity analysis to passive control of existing oscillations, and prevention of oscillations with ad hoc design modifications; (iv) accurate and efficient algorithms to perform uncertainty quantification of the stability calculations; (v) adjoint-based methods for optimization to suppress instabilities by placing acoustic dampers, and prevent instabilities by design modifications in the combustor's geometry; (vi) a methodology to gain physical insight in the stability mechanisms of thermoacoustic instability (intrinsic sensitivity); and (vii) in nonlinear periodic oscillations, the prediction of the amplitude of limit cycles with weakly nonlinear analysis, and the theoretical framework to calculate the sensitivity to design parameters of limit cycles with adjoint Floquet analysis. To show the robustness and versatility of adjoint methods, examples of applications are provided for different acoustic and flame models, both in longitudinal and annular combustors, with deterministic and probabilistic approaches. The successful application of adjoint sensitivity analysis to thermoacoustics opens up new possibilities for physical understanding, control and optimization to design safer, quieter, and cleaner aero-engines. The versatile methods proposed can be applied to other multiphysical and multiscale problems, such as fluid–structure interaction, with virtually no conceptual modification.

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“…wherec =c/c re f such thatc 2 = γp/ρ. The Laplace transform 13 of Eqn. (21) is the Helmholtz equation 14…”

Section: Helmholtz Equationmentioning

confidence: 99%

Section: Helmholtz Equationmentioning

confidence: 99%

See 1 more Smart Citation

Adjoint Methods as Design Tools in Thermoacoustics

Magri

2019

Applied Mechanics Reviews

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“…Nevertheless one disadvantage is the considerable computational cost because many simulations have to be performed to cover the range of excitation frequency and amplitude of interest. A computationally more efficient alternative to extract the FTF is to perform system identification (SI) of the flame response to a broadband excitation, a powerful technique which has been recently reviewed by Polifke [17] (one can also refer for instance to [23]). In the present work, a sequential combustor is treated as a single-input-single-output (SISO) Black Box, with temperature perturbations T at the inlet (input) and heat release rate response Q (output).…”

Section: Introductionmentioning

confidence: 99%

Autoignition flame dynamics in sequential combustors

Schulz

Noiray

2018

Combustion and Flame

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This numerical study deals with the heat release rate response of a sequential combustor flame to temperature perturbations. These flames are found in the new generation of gas turbine combustors, which are based on sequential combustion technologies. It is shown that the temperature perturbations T upstream of the fuel injection induce mixture fraction oscillations Z which also propagate toward the reaction zone, and that the combination of these two perturbations yields a strongly nonlinear heat release rate response Q . Large Eddy Simulation (LES) were performed using an Analytically Reduced Chemistry (ARC) mechanism, which includes 22 transported species in combination with the Dynamic Thickened Flame model (DTF). The burner flame transfer function (BFTF) giving the flame response with respect to T is obtained using a broadbandexcitation-based system identification (SI) as well as harmonic single frequency excitations. A simplified configuration with perfectly premixed conditions is considered to quantify the respective contributions of the different types of perturbation. These simulations highlight (i) the strong nonlinearity of the flame response to temperature perturbations, and (ii) the difficulty to break down the global flame response into independent driving mechanisms by making use of "simplified" configurations.

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“…They are commonly characterized as acoustic features of the combustion system driven by unsteady heat release of the flame, which feeds perturbation energy into acoustic cavityoriented resonant modes ( [3,4]). However, recent research, including theoretical modelling ( [5][6][7][8]), numerical simulations ( [9,10]) and experimental verifications ( [11][12][13]), show that thermoacoustic instability can occur even in a fully anechoic environment where acoustic reflections from the inlet or outlet of the combustor are not involved. Due to their independence on chamber acoustic resonant behavior, they are often identified as intrinsic thermoacoustic (ITA) instability.…”

Section: Introductionmentioning

confidence: 99%

Study an Acoustic-Intrinsic Thermoacoustic Feedback on Swirling Flame Combustors

Chen¹

2019

Proceedings of Global Power &Amp; Propulsion Society

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This paper investigates the intrinsic thermoacoustic feedback and its interaction with the cavity acoustic resonations in swirling flame combustors. The dynamics of acousticvortical-entropic perturbations due to the unsteady heat release rate in a swirling flame is given where the azimuthal and axial base flow velocities are present. The critical gain of the intrinsic thermoacoustic (ITA) oscillation is given meanwhile parametric analysis shows that the difference of the transit time between acoustic and vortical perturbations play an important role on the ITA critical gain. Applied to the verification of experimental results of a swirling flame combustor, the present work predicts correctly the thermoacoustic oscillations. Analysis on the interaction between the intrinsic thermoacoustic feedback and the traditional cavity acoustic resonation feedback shows that the thermoacoustic modes of the whole system are composed of both flame-induced modes and the cavity acoustic modes. The flame dynamics seems to be able to construct a virtual cavity feedback in the absence of acoustic feedbacks from the boundary conditions. The increase of the transit time difference between the acoustic and vortical perturbations before the flame front reduces the frequencies of flameinduced modes and worsens their stabilities. The cavity acoustic mode, on the other hand, forms a periodic orbit and approaches to the orbit's attractor.

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Numerical study on intrinsic thermoacoustic instability of a laminar premixed flame

Cited by 68 publications

References 36 publications

Adjoint Methods as Design Tools in Thermoacoustics

Adjoint Methods as Design Tools in Thermoacoustics

Autoignition flame dynamics in sequential combustors

Study an Acoustic-Intrinsic Thermoacoustic Feedback on Swirling Flame Combustors

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