High-speed imaging database of water jet disintegration Part II : Temporal analysis of the primary breakup

This paper is Part II of a series of articles focusing on the disintegration of a cylindrical (Ø=0.60 mm diameter) water jet in a quiescent atmosphere, from Rayleigh to early atomization breakup regimes. Liquid fluorescence high-speed imaging is used here, instead of shadowgraphy, providing a more faithful representation of liquid jet breakup dynamics as described in Part I (Roth et al., 2021). Using these data, the aim of this article is to perform a temporal analysis of the primary breakup process and to investigate the variation of breakup length in the time-domain, under each breakup regime. The results indicate that the liquid jet velocity at the onset of primary breakup oscillates within 6% of the liquid injection velocity for all considered operating conditions. The analysis of the dynamic instability is also performed, showing the growth rate of the first three high-energy-containing modes. The results confirm that there is no single disturbance at a specific frequency whose growth rate leads to liquid jet disintegration in the second wind-induced breakup regime and the early atomization regime. However, it is found that the dimensionless mean breakup length monotonically varies with the product of the dimensionless amplitude by the dimensionless temporal growth rate. The values provided for the dominant frequencies and growth rate of disturbances can be useful for modelers simulating the breakup of liquid jets in a quiescent atmosphere. Finally, the temporally resolved image series analyzed in this article can be further investigated and compared with simulation results, by downloading the processed image data on the website: https://spray-imaging.com/water-jet.html or alternatively on Open Science Framework at: https://doi.org/10.17605/OSF.IO/CG3D