The development of advanced low-emission aircraft engine technologies, along with reductions in noise from the airframe, fan, and jet exhaust, has made engine core noise a more prominent contributor. As a result, achieving future ambitious noise-reduction targets necessitates addressing noise generated by the engine core induced by the combustion processes (Ihme, 2017).
Our research at FxLab focuses on understanding and modeling direct and indirect combustion noise, their sources, generation mechanisms, and propagation. One way of understanding the combustion mechanism is through large-eddy simulation (LES) of turbulent combustion (Shao & Ihme, 2020; Shao et al., 2021). We focus on understanding the effects of different operating conditions on the combustion noise in a realistic, advanced gas-turbine combustor (Brouzet et al., 2024). Moreover, we develop a framework to allow efficient and accurate simulation of indirect combustion noise in the presence of complex geometries and flow conditions (O’Brien et al., 2015). This framework has been applied to study the effects of compositional inhomogeneities (Magri et al., 2016) in the combustor, as well as multi-modal, turbulent entropy fields (Brouzet et al., 2025) on the combustion noise.
References
2025
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Multi-modal effects on indirect noise induced by turbulent entropy fields
D. Brouzet, B. Krisna, and M. Ihme
Journal of Fluid Mechanics, May 2025
Planar entropy waves are commonly assumed for predicting indirect combustion noise. However, the non-planar and turbulent nature of flows found in most practical combustors challenges this assumption. In the present paper, we examine the indirect noise generated by non-planar and turbulent entropy fields through subsonic nozzles. Firstly, we introduce a new transfer function framework that accounts for the contribution of non-planar Fourier modes of the entropy field to the indirect noise spectra. When applied to a turbulent flow field, this method demonstrates a significant improvement in spectral predictions compared with a conventional approach that only considers the planar mode. Secondly, simulations show that non-planar Fourier modes become significant above a threshold frequency fthresh, found in the mid- to high-frequency range. This contribution of non-planar modes is explained by two-dimensional shear effects that distort the entropy waves. A scaling relation that uses residence times along streamlines is developed for fthresh, showing good agreement with simulation results. Finally, we show that the indirect noise from non-planar entropy modes found in aviation combustors can be significant at frequencies below 1 kHz, which might be relevant in situations of thermo-acoustic instabilities coupled to indirect noise.
2024
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Analysis of direct and indirect noise in a next-generation aviation gas turbine combustor
Davy Brouzet, Benyamin Krisna, Duane McCormick, C Aaron Reimann, Jeff Mendoza, and Matthias Ihme
Combustion and Flame, Feb 2024
A large-eddy simulation (LES) of a next-generation combustor is performed to examine effects of this combustor concepts on direct and indirect combustion noise characteristics. Direct noise is computed considering the unsteady heat release predictions while entropy fluctuations in the downstream part of the combustor are used to estimate indirect noise through the transfer function of the outlet nozzle. A low-order acoustic reconstruction technique, which utilizes the Green’s function of the configuration, is developed to compute the acoustics inside the combustor. Comparisons to experimental results are reported, showing the reasonable accuracy of the LES and combustion noise computations. The direct noise spectrum peaks at frequencies around 3 kHz because of the fast timescales associated with the chemical reactions inside the combustor. In addition, the indirect noise is dominant at low frequencies, i.e., less than 400 Hz, because of the characteristics of the entropy spectrum at the outlet nozzle. Compared to a conventional rich-quench-lean (RQL) combustor configuration, significant differences in the acoustics are observed, and are explained by two specific technological novelties. Firstly, the direct noise spectrum peaks at significantly higher frequencies due to the combustor’s compactness. Secondly, the entropy inhomogeneities downstream of the combustion region are an order of magnitude smaller in amplitude due to the lack of dilution with cold air. This leads to a significant reduction in the indirect noise amplitude at low frequencies, where it is the dominant source of noise. These results suggest opportunities for advanced combustion technologies to achieve substantial reductions in combustion-related noise.
2021
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Analysis of core-noise contributions in a realistic gas-turbine combustor operated near lean blow-out
Changxiao Shao, Kazuki Maeda, and Matthias Ihme
Proceedings of the Combustion Institute, Jan 2021
2020
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Effect of operating conditions on core noise for a realistic gas-turbine combustor
Changxiao Shao, and Matthias Ihme
Annual Research Briefs, Jan 2020
Publisher: Center for Turbulence Research
2017
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Combustion and engine-core noise
Matthias Ihme
Annual Review of Fluid Mechanics, Jan 2017
Publisher: Annual Reviews
2016
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Compositional inhomogeneities as a source of indirect combustion noise
Luca Magri, Jeff O’Brien, and Matthias Ihme
Journal of Fluid Mechanics, Jan 2016
Publisher: Cambridge University Press
2015
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Linear analysis of jet-engine core noise based upon high-fidelity combustor and turbine simulations
Jeffrey D O’Brien, Jeonglae Kim, and Matthias Ihme
In 53rd AIAA Aerospace Sciences Meeting, Jan 2015
