This paper deals with a detailed thermoacoustic assessment of an annular reheat combustor. Extensive tests have been conducted in the GT26 Test Power Plant in Switzerland. To this end, the combustion chamber has been instrumented with advanced pulsation sensors, an optical probe, strain gauges and accelerometers. A large number of dynamic pressure sensors recorded the acoustic pressure wave propagations in the axial and circumferential directions over a very large frequency range.A modal analysis technique has been developed to extract the acoustic mode shapes from the experimental data. This technique allows for decomposition in standing and traveling waves, hence revealing the nature of the acoustic field. The extracted mode shapes showed a very good agreement with results from 3-d finite element calculations.Combustion stability has been quantified by a methodology that extracts pulsation growth rates from experimental data. This novel method relies on advanced statistic processing of the instantaneous pulsation amplitudes. It has the advantage that it is insensitive to probe location, which is of particular advantage for high frequencies (higher than 1 kHz).
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