Accounting for Acoustic Damping in a Helmholtz Solver

Ni, Franchine; Miguel-Brebion, Maxence; Nicoud, Franck; Poinsot, Thiérry

doi:10.2514/1.j055248

Cited by 22 publications

(17 citation statements)

References 63 publications

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“…This linear model accounts for acoustic propagation and the effects of sudden area changes but all dissipation mechanisms are neglected. However, it is known that an important source of acoustic damping within the flow comes from the coupling between vortical structures generated in shear layers and acoustic waves [31][32][33].…”

Section: Discussionmentioning

confidence: 99%

Flame Describing Functions of a Confined Premixed Swirled Combustor With Upstream and Downstream Forcing

Gaudron

Gatti

Mirat

et al. 2019

Journal of Engineering for Gas Turbines and Power

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The frequency response of a confined premixed swirled flame is explored experimentally through the use of describing functions that depend on both the forcing frequency and the forcing level. In these experiments, the flame is forced by a loudspeaker connected to the bottom of the burner in the fresh gas region or by a set of loudspeakers connected to the combustion chamber exhaust tube in the burnt gas region. The experimental setup is equipped with a hot-wire (HW) probe and a microphone, both of which located in front of each other below the swirler. The forcing level is varied between |v′0|/v¯0=0.10 and 0.72 RMS, where v¯0 and v′0 are, respectively, the mean and the fluctuating velocity at the HW probe. An additional microphone is placed on a water-cooled waveguide connected to the combustion chamber backplate. A photomultiplier equipped with an OH* filter is used to measure the heat release rate fluctuations. The describing functions between the photomultiplier signal and the different pressure and velocity reference signals are then analyzed in the case of upstream and downstream forcing. The describing function measured for a given reference signal is shown to vary depending on the type of forcing. The impedance of the injector at the HW location is also determined for both upstream and downstream forcing. For all describing functions investigated, it is found that their phase lags do not depend on the forcing level, whereas their gains strongly depend on |v′0|/v¯0 for certain frequency ranges. It is furthermore shown that the flame describing function (FDF) measured with respect to the HW signal can be retrieved from the specific impedance at the HW location and the describing function determined with respect to the signal of the microphone located in front of the HW. This relationship is not valid when the signal from the microphone located at the combustion chamber backplate is considered. It is then shown that a one-dimensional (1D) acoustic model allows to reproduce the describing function computed with respect to the microphone signal inside the injector from the microphone signal located at the combustion chamber backplate in the case of downstream forcing. This relation does not hold for upstream forcing because of the acoustic dissipation across the swirler which is much larger compared to downstream forcing for a given forcing level set at the HW location. This study sheds light on the differences between upstream and downstream acoustic forcing when measuring describing functions. It is also shown that the upstream and downstream forcing techniques are equivalent only if the reference signal used to determine the FDF is the acoustic velocity in the fresh gases just before the flame.

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Section: Discussionmentioning

confidence: 99%

Flame Describing Functions of a Confined Premixed Swirled Combustor With Upstream and Downstream Forcing

Gaudron

Gatti

Mirat

et al. 2019

Journal of Engineering for Gas Turbines and Power

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“…An example of such a model is the ζ − l eff model [25,[55][56][57]. These types of acoustic loss models yield good results for swirling injectors [33,58], but they are linear. As a consequence, the predictions of the DATM coefficients according to these models do not depend on the forcing level and the nonlinearities observed in Fig.…”

Section: Cold Flow Operating Conditionsmentioning

confidence: 99%

Impact of the Acoustic Forcing Level on the Transfer Matrix of a Turbulent Swirling Combustor with and Without Flame

Gaudron

Gatti

Mirat

et al. 2019

Flow Turbulence Combust

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Thermoacoustic instabilities are a major issue for industrial and domestic burners. One possible framework to study these instabilities is to represent the system by a network of Dimensionless Acoustic Transfer Matrices (DATM) that link pressure and velocity fluctuations upstream and downstream each element of the network. In this article, the DATM coefficients of a turbulent swirling combustor are determined for a thermoacoustically stable configuration using harmonic acoustic forcing. Since the dynamics of the whole system is controlled by nonlinearities, the impact of the forcing level needs to be considered. The four DATM coefficients are thus measured for reactive operating conditions (premixed flame) and cold flow conditions for increasing acoustic excitation levels. The velocity level is controlled by a hot wire located inside the injector, in a region with a laminar top-hat velocity profile. The upstream and downstream specific acoustic impedances are also measured. Results for the acoustic response under cold flow conditions are first presented. In this case, the DATM coefficients are found to be independent of the forcing level except for the modulus of the coefficients linking the downstream velocity fluctuations to the upstream pressure and velocity fluctuations. This behavior is linked to the nonlinear response of the injector but is not entirely captured by the acoustic network model developed in this work. For reactive operating conditions, measurements indicate that all DATM coefficients depend on the forcing level to a certain extent. The Flame Describing Function, linking heat release rate fluctuations to velocity fluctuations, is used to reconstruct the transfer matrix through an acoustic network model. This network model accurately predicts the trend of the measured coefficients but the impact of the forcing level is not reproduced. Saturation for reactive operating conditions is shown to be not only related to the nonlinear flame response but also to the nonlinear injector dynamics. Finally, a data-driven reconstruction of the FDF using the acoustic network model along with the hot wire and microphone measurements is performed. This data-driven acoustic reconstruction is subsequently compared with the FDF determined with an optical technique.

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“…Indeed, several studies deduced matrix coefficients for acoustically passive combustor parts of varying complexity, e.g., a single orifice [3], a tandem orifice [4], multiperforated liner plates [5], or a premixed nozzle [6]. The acoustic transfer behavior of swirl generators, which are an unavoidable part in swirl stabilized combustion systems, was numerically determined by Gikadi et al [7] and Ni et al [8]. A system of algebraic equations may be constructed from the collection of transfer (or scattering) matrices of the combustor elements.…”

Section: Transfer and Scattering Matricesmentioning

confidence: 99%

“…Experience has shown that this kind of analysis provides not only quantitative data on stability limits and dynamics of a combustion system but also important physical insight [9,[11][12][13][14][15][16]. Several previous studies have concentrated on the transfer or scattering matrices of individual combustor elements such as a flame, a burner, a swirl nozzle, or a dissipative element [3][4][5][6]8,9,11,13,14,[17][18][19]. The present study concerns in an integrated fashion a combustor scattering matrix that includes swirler, injection tube, and flame as well as parts of the combustion chamber, see Fig.…”

Section: Transfer and Scattering Matricesmentioning

confidence: 99%

Direct Assessment of the Acoustic Scattering Matrix of a Turbulent Swirl Combustor by Combining System Identification, Large Eddy Simulation and Analytical Approaches

Merk

Silva

Polifke

et al. 2018

Journal of Engineering for Gas Turbines and Power

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This study assesses and compares two alternative approaches to determine the acoustic scattering matrix of a premixed turbulent swirl combustor: (1) The acoustic scattering matrix coefficients are obtained directly from a compressible large eddy simulation (LES). Specifically, the incoming and outgoing characteristic waves f and g extracted from the LES are used to determine the respective transmission and reflection coefficients via System Identification (SI) techniques. (2) The flame transfer function (FTF) is identified from LES time series data of upstream velocity and heat release rate. The transfer matrix of the reactive combustor is then derived by combining the FTF with the Rankine–Hugoniot (RH) relations across a compact heat source and a transfer matrix of the cold combustor, which is deduced from a linear network model. Linear algebraic transformation of the transfer matrix consequently yields the combustor scattering matrix. In a cross-comparison study that includes comprehensive experimental data, it is shown that both approaches successfully predict the scattering matrix of the reactive turbulent swirl combustor.

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Accounting for Acoustic Damping in a Helmholtz Solver

Cited by 22 publications

References 63 publications

Flame Describing Functions of a Confined Premixed Swirled Combustor With Upstream and Downstream Forcing

Flame Describing Functions of a Confined Premixed Swirled Combustor With Upstream and Downstream Forcing

Impact of the Acoustic Forcing Level on the Transfer Matrix of a Turbulent Swirling Combustor with and Without Flame

Direct Assessment of the Acoustic Scattering Matrix of a Turbulent Swirl Combustor by Combining System Identification, Large Eddy Simulation and Analytical Approaches

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