Sound generation by ducted flames

Hegde, U.; Reuter, D.; Zinn, B. T.

doi:10.2514/3.9930

Cited by 49 publications

(23 citation statements)

References 7 publications

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“…When such turbulent flames are confined in a combustion chamber, the confinement modes preferentially amplify the sound emitted from the flames at time scales close to their natural time scales (frequencies) and gives rise to the shallow peaks in the amplitude spectrum. The presence of multiple peaks in acoustic power spectrum during combustion inside a confinement is reported in literature (Chiu & Summerfield 1974;Kumar 1975;Strahle 1978;Hegde et al 1988). However, combustion chamber acoustics and hydrodynamics do not lock on during combustion noise and, hence, do not lead to the excitation of self sustained combustion instabilities (Chakravarthy et al 2007a;Chakravarthy, Sivakumar & Shreenivasan 2007b).…”

Section: Resultsmentioning

confidence: 86%

“…The confinement modes preferentially amplify the sound emitted from the flames at time scales close to their natural time scales (frequencies) and, hence, lead to multiple peaks in the acoustic power spectrum (Chiu & Summerfield 1974;Kumar 1975;Strahle 1978;Hegde, Reuter & Zinn 1988). As a consequence of these peaks in the acoustic power, the scale invariance of combustion noise in a confined environment is hard to discern in the power spectrum.…”

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confidence: 97%

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Combustion noise is scale-free: transition from scale-free to order at the onset of thermoacoustic instability

2015

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We investigate the scale invariance of combustion noise generated from turbulent reacting flows in a confined environment using complex networks. The time series data of unsteady pressure, which is the indicative of spatiotemporal changes happening in the combustor, is converted into complex networks using the visibility algorithm. We show that the complex networks obtained from the low-amplitude, aperiodic pressure fluctuations during combustion noise have scale-free structure. The power-law distributions of connections in the scale-free network are related to the scale invariance of combustion noise. We also show that the scale-free feature of combustion noise disappears and order emerges in the complex network topology during the transition from combustion noise to combustion instability. The use of complex networks enables us to formalize the identification of the pattern (i.e. scale-free to order) during the transition from combustion noise to thermoacoustic instability as a structural change in topology of the network.

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Section: Resultsmentioning

confidence: 86%

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confidence: 97%

Combustion noise is scale-free: transition from scale-free to order at the onset of thermoacoustic instability

2015

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“…The appropriate conservation conditions are applied across the combustion zone, any changes in cross-sectional area and where flow paths split or join. Together with the inlet and outlet boundary conditions this leads directly to the modal transfer functions, for example (p/q) n , in circumferential mode number n. By using the Green's function technique by Hedge et al 17 and the routine method of eigenfunctions to solve the Green's function, 18 the pressure response to a concentrated source…”

Section: 14 15mentioning

confidence: 99%

“…Now the local frequency spectrum of the heat release rate ψ q (ω) = κE q (κ)/ω is obtained by combining Eqs. (12)(13)(14)(15)(16)(17)(18). Moreover, it has been suggested in previous studies 12,28 that the correlation volume is V cor = 8 3 cor over the flame brush and cor ≈ δ T , the flame brush thickness.…”

Section: Iic Spectral Model For Heat Release Ratementioning

confidence: 99%

Prediction of Combustion Noise for an Aeroengine Combustor

Liu

Dowling²,

Swaminathan³

et al. 2014

Journal of Propulsion and Power

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Combustion noise may become an important noise source for lean-burn gas turbine engines, and this noise is usually associated with highly unsteady flames. This work aims to compute the broadband combustion noise spectrum for a realistic aeroengine combustor, and to compare with available measured noise data on a demonstrator aeroengine.A low-order linear network model is applied to a demonstrator engine combustor to obtain the transfer function that relates to unsteadiness in the rate of heat release, acoustic, entropic and vortical fluctuations. A spectral model is used for the heat release rate fluctuation, which is the source of the noise. The mean flow of the aeroengine combustor required as input data to this spectral model is obtained from RANS simulations. The computed acoustic field for a low-medium power setting indicates that the models used in this study capture the main characteristics of the broadband spectral shape of combustion noise. Reasonable agreement with the measured spectral level is achieved.

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“…Bloxsidge et al [9] performed a number of forcing experiments in which the phase relationships between various #uctuating parameters in a model afterburner were investigated to establish an empirical model. Changes in the #ow"eld were found to a!ect the generated sound indirectly through interaction with the heat release rate by Hedge et al [10] and they highlighted the importance of the e!ect of the coupling between the #ow"eld and the heat release on the resulting pressure #uctuations indicating that feedback was an important element of any model.…”

Section: Introductionmentioning

confidence: 99%