Experiments on axisymmetrically pulsed turbulent jet flames

Abstract

An experimental study of the effects of strong axisymmetric pulsing on a free, vertical turbulent jet diffusion flame is presented. The jet flame was pulsed over the frequency range of 2-1300 Hz with amplitudes ranging from 0.13-0.89 of the centerline jet velocity. Conditionally averaged centerline velocity measurements and flame photographs were obtained to characterize the pulsed jet flames. The centerline evolution of the pulse waveforms was examined and found to be dependent on the pulse frequency; the centerline decay of the pulse amplitude increased with increasing pulse frequency. The visual dimensions of the pulsed flame were also frequency dependent. Significant changes in the local flame structure were observed, which exhibited a constant local nondimensional frequency of about 0.2, consistent with a preferred-mode coupling between the pulsing and the jet flame structure. Several features of the results also suggest a coupling between the forcing and low frequency structure in the outer preheat layer surrounding the jet flame.