Imaging-based harmonic frequency analysis of a bluff-body premixed flame under acoustic excitations

The dynamic responses of a bluff-body premixed methane flame under acoustic excitations were studied using high speed color and schlieren imaging techniques. Two excitation frequencies at different amplitudes were tested and analyzed (50 Hz-105, 110, 115 dB and 200 Hz-120, 125, 130 dB). The fast Fourier transform (FFT) analysis reveals the dominant excitation frequency, as well as several harmonic frequencies as nonlinear responses. The dynamic mode decomposition (DMD) analysis was conducted using the time-resolved color and schlieren images to extract the spatial pattern at the dominant and multiplication harmonic frequencies. The results indicate that under these frequencies, the energy distribution has exhibited axisymmetric patterns to the nozzle axis, with positive and negative energy bands appearing alternatively. The spatial distribution has shown great variances under different excitation frequencies and amplitudes. An energy band sub-dividing phenomenon at multiplication frequencies was observed from the DMD results of both color and schlieren images. (C) 2021 Elsevier Masson SAS. All rights reserved.