Passive Control of the Inlet Acoustic Boundary of a Swirled Turbulent Burner

Abstract

The efficiency of perforated panels inserted in the injection line of a swirled turbulent burner is investigated as a passive control solution for combustion instabilities. Perforated panels backed by a cavity are widely used as acoustic liners, mostly in the hot gas region of combustion chambers to reduce pure tone noise levels. This paper focuses on the implementation of this technology in the injection line of a burner. The system is used to control the inlet acoustic reflection coefficient of the burner to stabilize the combustion. This method is shown to be particularly efficient because high acoustic fluxes issued from the combustion region are concentrated on a small surface area in the injection line. Theoretical results are used to design two types of perforated plates featuring similar acoustic damping properties when submitted to low amplitude pressure fluctuations (linear regime). However it is shown that their behavior largely differs when facing large pressure fluctuations levels (non linear regime) typical of those encountered during self-sustained combustion oscillations. Design criteria are given to control the reflection coefficient of perforated panels submitted to high pressure fluctuations levels and damp thermo-acoustic oscillations. While developed on a laboratory scale swirled combustor, this method is more general and could easily be adapted to practical combustors.