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research-article

Low-Order Modelling of Combustion Noise in an Aero-Engine: the Effect of Entropy Dispersion

[+] Author and Article Information
Yasser Mahmoudi

Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, Cambridge, UK
s.mahmoudilarimi@qub.ac.uk

Andrea Giusti

Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, Cambridge, UK
ag813@cam.ac.uk

Epaminondas Mastorakos

Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, Cambridge, UK
em257@eng.cam.ac.uk

Ann P. Dowling

Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, Cambridge, UK
apd1@cam.ac.uk

1Corresponding author.

ASME doi:10.1115/1.4037321 History: Received June 30, 2017; Revised July 13, 2017

Abstract

The present work studies the effect of entropy dispersion on the level of combustion noise at the turbine outlet of the Rolls-Royce ANTLE aero-engine. A new model for the decay of entropy waves, based on modelling dispersion effects, is developed and utilised in a low-order network model of the combustor (LOTAN). The proposed model for the dispersion of entropy waves only requires the mean velocity field as an input. LOTAN is then coupled with a low-order model (LINEARB) that studies propagation of combustion noise through turbine blades. By combining LOTAN and LINERAB, the combustion noise generated at the turbine exit is predicted. In comparison with experimental data it is found that without the inclusion of entropy dispersion, the level of combustion noise at the turbine exit is over-predicted by almost two orders of magnitude. The introduction of entropy dispersion in LOTAN results in much better agreement with the experimental data, highlighting the importance of entropy wave dispersion for the prediction of combustion noise in real engines. In more detail, the agreement with the experiment for high and low frequencies was very good. At intermediate frequencies the experimental measurements were still over-predicted, however the predicted noise was much smaller compared to the case without entropy dispersion. This discrepancy is attributed to the role of turbulent mixing in the overall decay of the entropy fluctuations inside the combustor and the absence of a proper model in LINEARB for the decay of entropy waves.

Copyright (c) 2017 by ASME
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