Novel perspectives on the modelling of combustion dynamics in thermoacoustic systems

Priya Subramanian (University of Leeds)

Frank Adams 1, Alan Turing Building,

Thermoacoustic systems consist of a source of unsteady heat release enclosed
in an acoustic field, e.g. gas turbines in power plants and aero-engines.
Self-sustaining large amplitude oscillatory instabilities arise in such
systems due to positive feedback between fluctuations in acoustic pressure
and unsteady heat release rate. During instability, excessive vibrations and
oscillatory thermal loads occur in the system which can lead to reduction of
operating life or even failure. Here we consider a simple thermoacoustic
system consisting of a laminar premixed flame enclosed in a duct that is
open at both ends. This talk explores three novel perspectives in modelling
the combustion dynamics and their resulting consequences for linear analysis
of stability of a thermoacoustic system:
(1) the non-orthogonality of the eigenvectors in a premixed flame
thermoacoustic system in causing subcritical transition to instability,
(2) the use of an impulse response function to identify constitutive
physical mechanisms in the response of the laminar premixed flame to
acoustic perturbations and
(3) the modelling of combustion dynamics in terms of a distributed time lag
response function in linear stability analysis, which allows for a
description that retains rich complexity as opposed to the popular single
time lag models

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