COHERENCE BETWEEN INTERNAL AND EXTERNAL NOISE GENERATED BY A GAS TURBINE COMBUSTOR.

Experiments and analysis on a gas turbine combustor unit are reported with a view in mind to separate propagated acoustic power from nonpropagating ″pseudosound″ . Analytically, it is suggested that a transition frequency will exist below which the interior pressure fluctuations are nonpropagating, whereas above this frequency, of the order of 100 Hz, the noise is dominated by propagating acoustic waves. Coherence measurements are reported which show this concept to be borne out experimentally. Coherence between interior and exterior microphones is measured over a range of experimental conditions for a gas turbine combustor exhausting directly to the atmosphere.