Acoustic and intrinsic thermoacoustic modes of a premixed combustor

Emmert, Thomas; Bomberg, Sebastian; Jaensch, S.; Polifke, Wolfgang

doi:10.1016/j.proci.2016.08.002

Cited by 59 publications

(45 citation statements)

References 11 publications

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“…(26). The solutions are the forward, f , and backward, g, acoustic waves (Riemann invariants), which travel at speedsc +ū andc −ū, respectively 15 . In addition, there exists an entropy wave, S e , which is convected with the mean flow at speedū, which generates an excess density [211].…”

Section: Helmholtz Equationmentioning

confidence: 99%

“…The assumption of a compact heat source physically signifies that there is no accumulation rate of mass, momentum 15 In other words, the characteristic lines are given by dx/dt =c ±ū 13 Fig. 3: Travelling-wave approach as applied to a longitudinal combustor with upstream (downstream) acoustic reflection coefficient R u (R d ) and entropic reflection coefficient, R e .…”

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%

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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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Section: Helmholtz Equationmentioning

confidence: 99%

Section: Helmholtz Equationmentioning

confidence: 99%

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Adjoint Methods as Design Tools in Thermoacoustics

Magri

2019

Applied Mechanics Reviews

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“…2 The characteristically high temperature of pure oxygen combustion can be controlled by recycling either the water vapor or CO 2 from the combustion products to form O 2 /H 2 O or O 2 /CO 2 oxidizer mixtures, respectively. 9 An amplifying pressure oscillation due to thermoacoustic instability can be among the factors leading to flame blowout similar to mixing and chemical time scales, and extinction strain rates. 3 Combustion instability is among the most critical operational challenges encountered in combustion systems of gas turbines, industrial boilers, furnaces, etc.…”

Section: Introductionmentioning

confidence: 99%

“…7,8 Therefore, thermoacoustic instability can occur even in an anechoic medium via flame intrinsic modes. 9 An amplifying pressure oscillation due to thermoacoustic instability can be among the factors leading to flame blowout similar to mixing and chemical time scales, and extinction strain rates. 10 Moreover, acoustic vibrations resulting from thermoacoustic instability are linked to combustors failure as a result of fatigue and reduced combustion efficiency.…”

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confidence: 99%