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research-article

Reconstruction and Analysis of the Acoustic Transfer Matrix of a Reheat Flame from Large-Eddy Simulations

[+] Author and Article Information
Mirko R. Bothien

Ansaldo Energia Switzerland, Römerstrasse 36, CH-5400 Baden
mirko.bothien@ansaldoenergia.com

Demian Lauper

Ansaldo Energia Switzerland, Römerstrasse 36, CH-5400 Baden
demian.lauper@gmail.com

Yang Yang

Ansaldo Energia Switzerland, Römerstrasse 36, CH-5400 Baden
yangyang@iet.cn

Alessandro Scarpato

Ansaldo Energia Switzerland, Römerstrasse 36, CH-5400 Baden
alessandro.scarpato@ansaldoenergia.com

1Corresponding author.

ASME doi:10.1115/1.4041151 History: Received July 02, 2018; Revised July 23, 2018

Abstract

Lean premix technology is widely spread in gas turbine combustion systems, allowing modern power plants to fulfill very stringent emission targets. These systems are, however, also prone to thermoacoustic instabilities, which can limit the engine operating window. The thermoacoustic analysis of a combustor is thus a key element in its development process. An important ingredient of this analysis is the characterization of the flame response to acoustic fluctuations, which is straightforward for lean premixed flames that are propagation stabilized, since it can be measured atmospherically. The present study deals with the flame response of mainly auto-ignition stabilized flames to acoustic and temperature fluctuations for which a CFD system identification approach is chosen. For propagation stabilized lean premixed flames, a common approach followed in the literature assumes that the acoustic pressure is constant across the flame and that the flame dynamics are governed by the response to velocity perturbations only. However this is not necessarily the case for reheat flames that are mainly auto-ignition stabilized. In this paper, a predominantly auto-ignition stabilized flame is described as a Multi-Input Multi-Output system and its full 2x2 transfer matrix is presented. Additionally, it is elaborated how in presence of temperature fluctuations the 2x2 matrix can be extended to a 3x3 matrix relating the primitive acoustic variables as well as the temperature fluctuations across the flame. It is shown that only taking the flame transfer function is insufficient to fully describe the dynamic behavior of reheat flames.

Copyright (c) 2018 by ASME
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