Measurement of Flame Describing Function of Jet Multinozzle Array Combustor and Prediction of Its Thermoacoustic Oscillation Frequency

Abstract To investigate the thermoacoustic instability characteristics of a jet multinozzle array combustor, this study experimentally measured the flame describing function (FDF) of the model combustor using methane fuel experiments, to investigate the effects of equivalence ratio and bulk velocity of the nozzle jet on the flame response. The measured FDFs were then incorporated into the low-order thermoacoustic network model, oscilos (open source combustion instability low order simulator), to predict thermoacoustic oscillations of the model combustor. Results show that within the bulk velocity range of 30 m/s to 60 m/s and equivalence ratio range of 0.64 to 0.76, the FDF gain decreases with increasing bulk velocity and equivalence ratio when û/u¯ = 0.1, while the characteristic peak frequency increases. The delay times extracted from the phase curves indicate that equivalence ratio fluctuation mechanism plays a dominant role in the generation and development of thermoacoustic oscillations. The FDF gain exhibits nonlinear characteristics when û/u¯ = 0.1 to 0.5, and thermoacoustic oscillations predictions of frequency using oscilos achieve an error margin within 8.0%.