Effect of the density ratio variation on the dynamics of a liquid jet injected into a gaseous cross-flow

In this paper, we investigate the effect of the density ratio on the primary atomization characteristics of a liquid jet injected into a gaseous crossflow. Jets into crossflow with a high density ratio can be challenging for some multiphase models with an interface reconstruction. In this case, it is common practice to artificially reduce the density ratio, keeping constant the dominant non-dimensional parameters, based on the assumption that keeping unaltered the non-dimensional numbers will also maintain the same atomization characteristics. The validity of this assumption is here investigated using large eddy simulations and a stochastic fields transported probability density function (PDF) method ( Σ-Y-PDF). A jet into crossflow, with a momentum flux ratio of 6.6 and Weber number of 330, is simulated. Two different density ratios are considered, 10 and 860, corresponding to the ones adopted in previous detailed numerical simulation and experimental investigations, respectively. We find that the liquid column breakup is influenced by the density ratio, with lateral ligaments formation observed only for the lower one. Also, the flow field is affected: decreasing the density ratio, the velocity increases in the wake region with recirculation observed. Furthermore, despite having the same Weber and Reynolds numbers, the two cases show different droplet size distributions. Smaller droplets are produced with the increase in the density ratio. Close to the liquid jet, the shape of the distribution is also affected. For the lower density ratio, a dichotomy is present, related to the presence of two distinct underlying breakup mechanisms, while increasing the density ratio, the dichotomy disappears.