On indirect noise in multicomponent nozzle flows

Magri, Luca

doi:10.1017/jfm.2017.591

Cited by 28 publications

(72 citation statements)

References 25 publications

(43 reference statements)

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“…is the volumetric heat release rate due to reaction, and γ is the heat capacity ratio. Gibbs' rela-tion (4) simplifies to [195] ds c p = dp…”

Section: Under These Assumptions the Nonlinear Dimensional Equationsmentioning

confidence: 99%

“…are the species' chemical potential function and heatcapacity factor, respectively [195,196]. The energy equation formulated with the entropy variable (5) simplifies to…”

Section: Under These Assumptions the Nonlinear Dimensional Equationsmentioning

confidence: 99%

“…In addition, there exists an entropy wave, S e , which is convected with the mean flow at speedū, which generates an excess density [211]. Modelling a multi-component mixture creates additional excess density [195]. Figure 3 shows a schematic of the longitudinal combustor modelled with the wave approach.…”

Section: Helmholtz Equationmentioning

confidence: 99%

“…Quantum mechanics offers a large "repository" of mathematical techniques, some of which can be adapted to tackle acoustic/thermoacoustic problems. For example, some aeroacoustic problems can be cast in a Schrödinger equation and solved by Dyson expansion[195]. There are other examples, which will be the subject of another study.…”

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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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“…is the volumetric heat release rate due to reaction, and γ is the heat capacity ratio. Gibbs' rela-tion (4) simplifies to [195] ds c p = dp…”

Section: Under These Assumptions the Nonlinear Dimensional Equationsmentioning

confidence: 99%

“…are the species' chemical potential function and heatcapacity factor, respectively [195,196]. The energy equation formulated with the entropy variable (5) simplifies to…”

Section: Under These Assumptions the Nonlinear Dimensional Equationsmentioning

confidence: 99%

Section: Helmholtz Equationmentioning

confidence: 99%

mentioning

confidence: 99%

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Adjoint Methods as Design Tools in Thermoacoustics

Magri

2019

Applied Mechanics Reviews

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“…Fuel e↵ects were studied by [18]. The general theory, which considers fluctuations in the heat capacities as well, is presented in [16], where a mathematical solution of the multicomponent aeroacoustic problem was proposed. In order to characterize the compositional inhomogeneities for the aeroacoustic calculations, [5,17,18] modeled the complex combustion dynamics and mixing with simple flamelet calculations.…”

Section: Introductionmentioning

confidence: 99%

Flow Inhomogeneities in a Realistic Aeronautical Gas-Turbine Combustor: Formation, Evolution and Indirect Noise

Giusti

Magri

Zedda

2018

Volume 4B: Combustion, Fuels, and Emissions

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Indirect noise generated by the acceleration of combustion inhomogeneities is an important aspect in the design of aeroengines because of its impact on the overall noise emitted by an aircraft and the possible contribution to combustion instabilities. In this study, a realistic rich-quench-lean combustor is numerically investigated, with the objective of quantitatively analyzing the formation and evolution of flow inhomogeneities and determine the level of indirect combustion noise in the nozzle guide vane (NGV). Both entropy and compositional noise are calculated in this work. A high-fidelity numerical simulation of the combustion chamber, based on the Large-Eddy Simulation (LES) approach with the Conditional Moment Closure (CMC) combustion model, is performed. The contributions of the different air streams to the formation of flow inhomogeneities are pinned down and separated with seven dedicated passive scalars. LES-CMC results are then used to determine the acoustic sources to feed an NGV aeroacoustic model, which outputs the noise generated by entropy and compositional inhomogeneities. Results show that non-negligible fluctuations of temperature and composition reach the combustor’s exit. Combustion inhomogeneities originate both from finite-rate chemistry effects and incomplete mixing. In particular, the role of mixing with dilution and liner air flows on the level of combustion inhomogeneities at the combustor’s exit is highlighted. The species that most contribute to indirect noise are identified and the transfer functions of a realistic NGV are computed. The noise level indicates that indirect noise generated by temperature fluctuations is larger that the indirect noise generated by compositional inhomogeneities, although the latter is not negligible and is expected to become louder in supersonic nozzles. It is also shown that relatively small fluctuations of the local flame structure can lead to significant variations of the nozzle transfer function, whose gain increases with the Mach number. This highlights the necessity of an on-line solution of the local flame structure, which is performed in this paper by CMC, for an accurate prediction of the level of compositional noise. This study opens new possibilities for the identification, separation and calculation of the sources of indirect combustion noise in realistic aeronautical gas turbines.

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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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On indirect noise in multicomponent nozzle flows

Cited by 28 publications

References 25 publications

Adjoint Methods as Design Tools in Thermoacoustics

Adjoint Methods as Design Tools in Thermoacoustics

Flow Inhomogeneities in a Realistic Aeronautical Gas-Turbine Combustor: Formation, Evolution and Indirect Noise

Autoignition flame dynamics in sequential combustors

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