Self-pulsation characteristics of gas-liquid swirl coaxial atomizer with serrated gas jet nozzle

The self-pulsation phenomenon, commonly observed in gas-liquid coaxial injectors under certain flow conditions, is a result of the shear layer instability between the two fluids. The self-pulsating spray possesses a global mode with intrinsic frequency, which is undesirable in the context of thermoacoustic stability of the combustors. The dynamics of the central gas jet possibly governs the self-pulsation phenomenon and hence the present experiments focus on the effect of serrated gas jet exit (like chevron nozzles) on the pulsation characteristics of the gas-centered swirl coaxial injector. Time-resolved shadowgraphy images of the spray are captured near the injector with different recess values. The POD analysis of the spray images highlights a distortion of the pulsating mode to an azimuthal mode with the serrated gas jet exit when the recess is relatively high. The sharp frequency peak of the spectrum from the temporal coefficients gets suppressed and changed into a broadband mode indicating the breakdown of the periodically self-oscillating flow. The loss of coherence in the gas jet may be the possible cause of suppression of self-pulsation. However, at a low recess, the pulsating modes are still prevalent indicating the strong influence of the recess.