Effect of distributed heat source on low frequency thermoacoustic instabilities

“…It has great potential to be implemented in combustioninvolved engines. [103][104][105][106][107][108][109][110][111][112][113][114] The acoustic damping performance of such coupled Helmholtz resonators is also related to the structures. [115][116][117][118][119] The conventional theoretical model 120,121 may not be applicable like the experimental 122,123 and numerical approaches 124,125 as discussed in the present work.…”

Section: Model Validationmentioning

confidence: 99%

Case studies on aeroacoustics damping performances of Coupled Helmholtz Resonators over low frequency ranges

Zhang

Win

2022

Journal of Low Frequency Noise, Vibration and Active Control

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Helmholtz resonators are widely applied in industries to reduce the transmission of unwanted noise and passively attenuate tonal noise in pipes/ducts. For example, internal combustion engines take advantage of Helmholtz resonators by combining air box, subwoofers and perforated pipes/plates to reduce engine noise emission nowadays. However, the main drawback of the conventional Helmholtz resonators includes a very narrow bandwidth. To broaden the effective noise damping frequency range of Helmholtz resonators, a number of different improved designs are reported and tested recently in the literature such as applying an array of separated resonators or implementing mechanical-coupled Helmholtz resonators. In this work, we conduct a brief review on the aeroacoustics damping performance of coupled Helmholtz resonators over low frequency range. The noise damping performances could be characterized and quantified in terms of transmission loss and sound absorption coefficient. Both definitions are discussed. Comparison is then made between the separately working resonators and the mechanical-coupled ones. This is achieved by replacing the sharable flexible sidewall with a rigid sidewall. The effect of the mean grazing flow is also discussed and examined on the noise damping performances. An experimental case study of the present authors is included. Additionally, to improve the noise damping performance further, an overview of the resonators neck with different noise damping materials inserted is conducted. Finally, 3D numerical approaches in simulating the aeroacoustics damping performances of coupled Helmholtz resonators are reviewed. This case study and brief overview provides a guidance on improving the design of coupled Helmholtz resonators and an array of Helmholtz resonators.

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“…In recent years, the effects of distributed heat sources on thermoacoustic instability have attracted more and more attention. Li 33,34 studied the effect of non-uniform circumferential and axial distribution of heat release rate on a thermoacoustic system by establishing a three-dimensional thermoacoustic model. It was found that the non-uniform circumferential distribution has a significant effect on the oscillation frequency and growth rate.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the stability of the Rijke-type thermoacoustic system with an axially distributed heat source

Pang,

Wang,

et al. 2023

Journal of Low Frequency Noise, Vibration and Active Control

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Due to the incurred damages to the combustors, large-amplitude self-sustained thermoacoustic oscillations are unwanted in many propulsion systems, such as liquid/solid rocket motors and aero-engines. To suppress these thermoacoustic oscillations efficiently, the mechanism of thermoacoustic instability needs to be clarified. Following the previous experimental work, the transitions to instability in a Rijke-type thermoacoustic system with an axially distributed heat source are studied numerically in this paper. The URANS numerical method is utilized and verified by means of a mesh sensitivity analysis. The influences of the axially distributed heater length, the heater location, and the mean flow velocity on the nonlinear dynamic behaviors of thermoacoustic oscillations are evaluated. To explore the corresponding mechanism behind these influences, the principle of acoustic energy conservation has been applied. The acoustic energy gains from the thermal-acoustic coupling are quantified via Rayleigh’s integral, and their phase differences are calculated by the cross-correlation function. The acoustic damping induced by the vortex dissipation is qualitatively analyzed by the characteristics of the flow fields in the Rijke tube. Finally, as the heater length, the heater location, or the mean flow velocity is varied, three mechanisms of the transitions to instability in a Rijke-type thermoacoustic system are identified.

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Effect of distributed heat source on low frequency thermoacoustic instabilities

Cited by 23 publications

References 12 publications

Prediction of stability behaviors of longitudinal and circumferential eigenmodes in a choked thermoacoustic combustor

Prediction of stability behaviors of longitudinal and circumferential eigenmodes in a choked thermoacoustic combustor

Case studies on aeroacoustics damping performances of Coupled Helmholtz Resonators over low frequency ranges

Investigation on the stability of the Rijke-type thermoacoustic system with an axially distributed heat source

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