A drop-shattering collision model for multidimensional spray computations

A simplified model of drop-shattering collision is proposed. It is assumed that two droplets collide with a sufficient collisional Weber number that they are transformed into a long cylindrical liquid ligament. As this ligament elongates under the impulse of the collision, based on Rayleigh linear jet breakup theory, capillary wave-induced disturbances grow, and if the time needed for them to develop is shorter than the time taken by the two ends of the cylinder to retract, they eventually break it into droplets. Drop-shattering breakup in the short-ligament regime is not considered in the present model. The equation of the dynamics of elongating and retracting cylindrical liquid ligaments is derived and analyzed. The model was also implemented into the multidimensional KIVA-II code. Experiments on the collisional behavior of hydrocarbon droplets of Hung and Martin [1] were used for model validation. These experiments consider the collision of two aerodynamically stable streams of droplets at three different intersection angles. The predicted size and velocity distributions of the children droplets are compared with the experimental results obtained with phase Doppler particle analysis. Although the sizes and velocities of the droplets are somewhat overpredicted, the model is able to predict atomization due to collisions. The model was also tested in a high-pressure, nonevaporating diesel spray to assess the influence of drop shattering. The results show that collisions involving shattering collisions seem to be very likely to occur in diesel sprays, and a deeper understanding of spray physics in this regime and a better prediction are obtained.