A Study of Droplet Breakup in the Vicinity of an Airfoil

Supercooled large droplets can breakup before imping on aerodynamic surfaces and this should be taken into account in the icing codes. A study of droplets breakup in the vicinity of an airfoil has been conducted. Experiments for streams of droplets that were allowed to fall in the path of an incoming airfoil attached to a rotatory arm were conducted at the INTA facility. Droplets diameters ranged from 500 μm to 3 mm and two airfoils models of leading edge radius of 70 mm and 103 mm moving at velocities of 70 m/s, 80 m/s and 90 m/s were tested. Two subsets of experimental data for both bag and stamen breakup and shear breakup modes were used in this investigation. For these cases a numerical trajectory and deformation model was applied to obtain the evolution of the horizontal position, and the droplet maximum and minimum diameter. Breakup onset was determined from experimental data. Though previous works considered that breakup starts when there is a minimum in the minimum diameter, such minimum was not found in the integration of the model. However, it was found a minimum in the derivative of the minimum diameter at the breakup onset. The implication of this finding has been discussed. Additionally, the minimum in the derivative of the minimum diameter is compared to a previous empirical breakup criterion and the results of the comparison have been discussed.