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1.Combustion noise.pdf
Introduction
The purpose of this note is to describe the theoretical model supporting the evaluation of
combustion noise. Combustion noise is induced by the heat release rate related to the combustion
process. A major combustion noise issue is the possible occurrence of thermo-acoustic
instabilities. Such phenomena is characterized by the generation of acoustic tones within the
combustion system and can aect any combustion device where the burner/
ame is conned
in a vessel (industrial burners, domestic heating appliances, gas turbines, rocket engines, etc).
Thermo-acoustic oscillations result from a feedback loop between the acoustic eld and the
ame heat release rate. If these oscillations are unstable, signicant damage and/or loss of
performances can be encountered. It is therefore necessary to be able to predict accurately such
phenomena.
The theoretical model is rst developed in the context of linearized Euler equations. Both
momentum, continuity and energy equations are summarized with a particular attention for the
handling of the heat release rate in the energy equation. Such equations involve ve unknowns
(pressure, density and velocity
uctuations). Reduction to a scalar wave equation involving the
pressure
uctuation is then presented for the no-
ow case. Particular
ame models are described
in order to better characterize the source and its interaction with the generated sound eld. Themain features of the n