Journal of Fluid Mechanics

Table of Contents - Volume 733 - 2013  

Rapids

The dissipation and shear dispersion of entropy waves in combustor thermoacoustics

Aimee S. Morgansa1 c1, Chee Su Goha1 and Jeremy A. Dahana1

a1 Department of Aeronautics, Imperial College London, London SW7 2AZ, UK

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.

(Received June 06 2013)

(Revised August 02 2013)

(Accepted August 21 2013)

(Online publication September 23 2013)

Key words

  • acoustics;
  • combustion

Correspondence

c1 Email address for correspondence: a.morgans@imperial.ac.uk

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