Indirect Combustion Noise: Experimental Investigation of the Vortex Sound Generation in a Choked Convergent-divergent Nozzle

Nancy Kings , Lars Enghardt , Friedrich Bake

Combustion noise in gas turbines consists of direct noise related to the unsteady combustion process itself and indirect noise. The latter is produced by vorticity or entropy fluctuations originating from the combustor as they accelerate when passing through the turbine. The sound generation mechanism through the acceleration of vorticity alterations was studied in a model experiment. Within a swirl-free and a swirling tube flow, vorticity fluctuations were generated artificially by injecting temporally additional air into the mean flow which were convected and accelerated in a choked convergent-divergent nozzle. The produced acoustic waves were detected downstream of the nozzle. In addition, the spatial and temporal changes of the velocity field upstream of the nozzle were determined with Hot-Wire Anemometry measurements. Direct and vortex sound was identified and separated by varying the distance between the air-injection inlet and the nozzle. The intensity of the swirling flow and of the vorticity fluctuation was modified. Increasing the air-injection into the mean flow augments the generated indirect noise.

Mots clés: Indirect Combustion Noise; Vortex Sound

Domaines: Acoustique [physics.class-ph]

Nancy Kings, Lars Enghardt, Friedrich Bake. Indirect Combustion Noise: Experimental Investigation of the Vortex Sound Generation in a Choked Convergent-divergent Nozzle. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00811052⟩