New droplet aero-breakup mechanism associated to unsteady flow loading

Abstract

Experimental testing on the unsteady aero-breakup of ethyl alcohol droplets was carried out at the rotating arm facility of INTA. The selection of the working fluid was driven by the need to explore wider ranges of the dimensionless parameters that govern the problem. A model airfoil was attached at the end of a 2.3 m long rotating arm driven by an electric motor. Droplets, whose diameter ranged from 500 mm to 1500 mm, were allow to fall in the path of the airfoil that attained velocities in the range between 30 m/s and 60 m/s. Droplets trajectories and breakup modes were recorded, and a new breakup mode was identified. Its sequence is as follows: 1) the droplet deforms as an oblate spheroid, 2) a bulge appears and grows on its flow facing surface, 3) the droplet thickens in the stream-wise direction; 4) the thickening in the rear part of the droplet develops in the shape of a cone, 5) the cone grows thinner until a finger like shape is formed. Additionally, based on a theoretical model developed by the authors, a comparison has been made between the deformation and breakup onset phases of ethyl-alcohol and water droplets up to the instant of breakup.