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2.2.2 Oblique Drop Impact
The oblique impact is obviously a frequent occurrence in the in-flight icing, because
the normal impact takes place only at the stagnation point. The oblique
impact of single drops distinguishes from the normal impact by exhibiting very
different splash modes: aerodynamic breakup, partial rebounding and total rebounding.
The latter two are reminiscences of the drop impact on hydrophobic
surfaces.
Povarov et al. [113] conducted the drop impact on a rotating disk in order to
observe the interaction between the drop and the boundary layer above the disk.
The drops had diameters from 0.3 mm to 4.0 mm and a falling velocity of 0.1m/s
to 10m/s. The horizontal rotating disk has an azimuthal velocity up to 60m/s at
the radial position of impact. At lower rotational speed, the drop spread on the
disk, and eventually broke up by the airflow. As the rotational speed increased, the
drop barely touched the surface before it was blown away by the airflow. Typical
observations are shown in Figure 2.10.
(a) Drop diameter: 2 mm, velocity of the
impact surface: 30m/s.
(b) Drop diameter: 2 mm, velocity of the
impact surface: 60m/s.
Figure 2.10.: Interaction of a falling drop with the gas boundary layer on a rotating
surface, reported by Povarov et al. [113]. The sequence of the image
are indicated by the number on the upper left corner.
2.2. Drop Impact on Dry Surfaces 23