Large-Scale Vortical Motion and Pressure Fluctuation in Noise-Controlled, Swirl-Stabilized Combustor

Abstract

To clarify the mechanisms of combustion oscillation, combustion noise and their suppression by secondary fuel injection, simultaneous measurements of stereoscopic particle image velocimetry (SPIV) and pressure fluctuation in combustion chamber were conducted on several planes of a swirl-stabilized turbulent premixed flame for no control case and noise-controlled case by continuous secondary fuel injection. Velocities measured by SPIV were averaged in 8 phases of the pressure fluctuation and streamlines were obtained from the phase-averaged velocities. For no control case, large-scale vortical structures are generated in regions around the axial centerline of the combustor and outer edge of the swirl nozzle in the phase of low pressure. With increasing pressure, they move near the contour surface of mean progress variable (c) over bar = 0.5 which have been obtained in the previous study. These large-scale vortical motions induce fluctuation of flame front and enhance entropy term in the acoustic sound source. The secondary fuel injection suppresses the velocity fluctuation in the inner recirculation zone, resulting in reduction of combustion noise. These results show that control of the large-scale vortical motion is important for reduction of combustion noise.