front page - tuprints - Technische Universität Darmstadt

Supplementarily, Zen et al. [175] published the top view of the asymmetric splash
as shown in Figure 2.13. It is interesting to notice that the uprising liquid ligament
was barely connected to the spreading lamella.
Figure 2.13.: Side view and top view of the asymmetric splash in an oblique impact,
provided by Zen et al. [175].
Splash threshold for the asymmetric splash was provided by Bird et al. as [18]
We Re 1/2
1 − 2.5 v t
v n
Re −1/2 2
> K crit = 5700, (2.13)
where v t and v n are respectively tangent and normal components of the impact
velocity, the coefficient 2.5 and the threshold value K crit = 5700 were found out
with the experimental data. This model is consistent with Eq. 2.11 provided by
Mundo et al. although the threshold value was a lot higher because of a lower
roughness. This threshold takes the tangent velocity into consideration, but the
importance of the surrounding gas is missing.
It should be noted that the experiment of Mundo et al. [99] comprised exclusively
oblique impact with the impingement angle between 4° and 65°. However, only
the normal velocity entered the splash threshold, whereas the significance of the
tangent velocity was unrecognized. The reason lies probably at the very rough
surface as well as the possible liquid film on the impact surface.
2.2.3 High-speed Drop Impact
The velocity the aircraft in an in-flight icing event is of the order of 100m/s. Highspeed
impact of single drops is of interest. Mehdizadeh et al. [83] and Dhiman et
al. [37] conducted single drop impacts on a rotating target with a high tangential
velocity up to 50m/s. The drop diameter ranged between 0.5 mm and 1.33 mm.
Strong prompt splash as well as rupture of the liquid film was observed as Figure
2.2. Drop Impact on Dry Surfaces 25