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FLOW INHOMOGENEITIES IN A REALISTIC AERONAUTICAL GAS-TURBINE COMBUSTOR: FORMATION, EVOLUTION AND INDIRECT NOISE

[+] Author and Article Information
Andrea Giusti

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

Luca Magri

Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, United Kingdom
lm547@cam.ac.uk

Marco Zedda

Combustion Aerothermal Methods, Rolls-Royce plc., PO Box 31, DE24 8BJ, Derby, United Kingdom
marco.zedda@rolls-royce.com

1Corresponding author.

ASME doi:10.1115/1.4040810 History: Received March 23, 2018; Revised June 15, 2018

Abstract

A high-fidelity numerical simulation of a realistic combustion chamber, based on the Large-Eddy Simulation (LES) approach with the Conditional Moment Closure (CMC) combustion model, is performed. The contributions of the different air streams to the formation of flow inhomogeneities are pinned down and separated with seven dedicated passive scalars. LES-CMC results are then used to determine the acoustic sources to feed an NGV aeroacoustic model, which outputs the noise generated by entropy and compositional inhomogeneities. Results show that non-negligible fluctuations of temperature and composition reach the combustor's exit. Combustion inhomogeneities originate both from finite-rate chemistry effects and incomplete mixing. In particular, the role of mixing with dilution and liner air flows on the level of combustion inhomogeneities at the combustor's exit is highlighted. The species that most contribute to indirect noise are identified and the transfer functions of a realistic NGV are computed. The noise level indicates that indirect noise generated by temperature fluctuations is larger that the indirect noise generated by compositional inhomogeneities, although the latter is not negligible and is expected to become louder in supersonic nozzles. It is also shown that relatively small fluctuations of the local flame structure can lead to significant variations of the nozzle transfer function, whose gain increases with the Mach number. This highlights the necessity of an on-line solution of the local flame structure, which is performed in this paper by CMC, for an accurate prediction of the level of compositional noise.

Copyright (c) 2018 by ASME
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