The drive to low emissions from GT combustors has pushed manufacturers towards leaner combustion systems. Lean combustion systems are susceptible to thermo acoustic or combustion instabilities, which can significantly limit the operation of the GT in terms of performance and emissions. Combustion instability is the result of coupling between fluctuations in the heat release rate and pressure waves. The occurrence of instability dependent on (a) satisfying the Rayleigh criterion and (b) the growth must exceed the losses of acoustic energy. The growth of instability can be controlled by increasing the level of acoustic damping via a Helmholtz resonator and through viscous damping. Design rules for a passive damper have been developed through the EU funded project called PRECCINSTA (Prediction and control of combustion instabilities in tubular and annular combustion systems) by the University of Cambridge. These design rules are for a doubled-skinned perforated liner where a biasing flow is used to dissipated sound energy. The sound dissipation mechanism is via vortex formation. These design rules were then validated against atmospheric and intermediate pressure combustion tests at Rolls-Royce for self-excited and forced excited oscillations. This paper summaries these tests and gives the results for a simple perforated liner as a passive acoustic damper.

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