TY - JOUR
T1 - Analysis of degenerate mechanisms triggering finite-amplitude thermo-acoustic oscillations in annular combustors
AU - Murthy, Sandeep R.
AU - Sayadi, Taraneh
AU - Le Chenadec, Vincent
AU - Schmid, Peter J.
AU - Bodony, Daniel J.
N1 - Generated from Scopus record by KAUST IRTS on 2022-09-13
PY - 2019/12/25
Y1 - 2019/12/25
N2 - A simplified model is introduced to study finite-amplitude thermo-acoustic oscillations in -periodic annular combustion devices. Such oscillations yield undesirable effects and can be triggered by a positive feedback between heat-release and pressure fluctuations. The proposed model, comprising the governing equations linearized in the acoustic limit, and with each burner modelled as a one-dimensional system with acoustic damping and a compact heat source, is used to study the instability caused by cross-sector coupling. The coupling between the sectors is included by solving the one-dimensional acoustic jump conditions at the locations where the burners are coupled to the annular chambers of the combustion device. The analysis takes advantage of the block-circulant structure of the underlying stability equations to develop an efficient methodology to describe the onset of azimuthally synchronized motion. A modal analysis reveals the dominance of global instabilities (encompassing the large-scale dynamics of the entire system), while a non-modal analysis reveals a strong response to harmonic excitation at forcing frequencies far from the eigenfrequencies, when the overall system is linearly stable. In all presented cases, large-scale, azimuthally synchronized (coupled) motion is observed. The relevance of the non-modal response is further emphasized by demonstrating the subcritical nature of the system's Hopf point via an asymptotic expansion of a nonlinear model representing the compact heat source within each burner.
AB - A simplified model is introduced to study finite-amplitude thermo-acoustic oscillations in -periodic annular combustion devices. Such oscillations yield undesirable effects and can be triggered by a positive feedback between heat-release and pressure fluctuations. The proposed model, comprising the governing equations linearized in the acoustic limit, and with each burner modelled as a one-dimensional system with acoustic damping and a compact heat source, is used to study the instability caused by cross-sector coupling. The coupling between the sectors is included by solving the one-dimensional acoustic jump conditions at the locations where the burners are coupled to the annular chambers of the combustion device. The analysis takes advantage of the block-circulant structure of the underlying stability equations to develop an efficient methodology to describe the onset of azimuthally synchronized motion. A modal analysis reveals the dominance of global instabilities (encompassing the large-scale dynamics of the entire system), while a non-modal analysis reveals a strong response to harmonic excitation at forcing frequencies far from the eigenfrequencies, when the overall system is linearly stable. In all presented cases, large-scale, azimuthally synchronized (coupled) motion is observed. The relevance of the non-modal response is further emphasized by demonstrating the subcritical nature of the system's Hopf point via an asymptotic expansion of a nonlinear model representing the compact heat source within each burner.
UR - https://www.cambridge.org/core/product/identifier/S0022112019007201/type/journal_article
UR - http://www.scopus.com/inward/record.url?scp=85074248098&partnerID=8YFLogxK
U2 - 10.1017/jfm.2019.720
DO - 10.1017/jfm.2019.720
M3 - Article
SN - 1469-7645
VL - 881
SP - 384
EP - 419
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
ER -