Coaxial elements and annular liquid jets are normally utilized in industrial applications to generate sprays. A particle image velocimetry investigation on the transient characteristics of the spray velocity field of a coaxial convergent nozzle is carried out in this paper. Based on the measurement results, spectrum analysis is performed to detect the process of atomization in the spray. Experimental results show that at large gas jet velocities, the process of generation of droplets is controlled mainly by the dynamics of liquid ligaments, and the power spectrum reveals that the velocity fluctuations are superimposed on the transient flow field by the effect of the shear layer instability. With the increase of gas velocity, the fluctuations of the spray velocity develop progressively to higher frequencies.

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