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The dissipation and shear dispersion of entropy waves in combustor thermoacoustics

Published online by Cambridge University Press:  23 September 2013

Aimee S. Morgans ,
Chee Su Goh  and
Jeremy A. Dahan
Aimee S. Morgans*
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
Chee Su Goh
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
Jeremy A. Dahan
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
*
†Email address for correspondence: [email protected]
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Abstract

This paper considers the effect of flow advection on entropy waves. The interest is in whether entropy waves persist in gas turbine combustors, between the flame, where they are generated, and the combustor exit, where their acceleration generates acoustic waves (known as ‘entropy noise’ or ‘indirect combustion noise’). Entropy wave advection within a simplified fully developed turbulent channel-flow simulation is investigated. Entropy wave dissipation is found to be negligible, with loss of entropy wave strength caused predominantly by mean flow shear dispersion. The impulse response of entropy perturbations downstream of where they are generated is shown to be well modelled by a Gaussian profile in time. This yields a (different) Gaussian form for the inlet–outlet transfer function of entropy perturbations. For representative gas turbine flows, the magnitude of this transfer function is such that significant entropy wave strength will remain at the combustor exit, confirming that entropy-generated acoustic waves are likely to be important.

JFM classification

Acoustics: Acoustics Reacting Flows: Combustion
Type
Rapids
Information
Journal of Fluid Mechanics , Volume 733 , 25 October 2013 , R2
Copyright
©2013 Cambridge University Press 

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