Drop Impact on Dry Surfaces with Phase Change

Airframe icing caused by the Supercooled Large Droplet (SLD) has been identified as a severe hazard of aviation. The impact of SLD in the in-flight icing condition remains unknown in multiple aspects. The accompanying drop splash invalidates the current engineering tools for design of the anti-icing system, and the involvement of supercooling in drop impact demands exploration. In the framework of the EU Project EXTICE and DFG project SFB - TRR 75, this thesis contributes to understanding of the impact of SLD by two experimental investigations, respectively on the effect of supercooling on drop impacts and the drop splash after high-speed impact.

Supercooled drops were created, and the drop impact with phase change was observed by both shadowgraph imaging and infrared imaging. The dynamic spreading diameter of the drop impact on aluminum surfaces was measured. It was found that the phase change was negligible for drop impacts in typical icing conditions. The drop receding on the hydrophobic surface was influenced by the contact temperature, which was measured by the infrared imaging.

High speed impacts of single drops with diameters ranging from 130µm to 200µm on dry surfaces of rapid motion were recorded by shadowgraph imaging up to 1 Mfps. The target velocity varied from 10m/s to 63m/s. The impact surface had an inclination ranging from 0° to 75° in order to investigate the effects of oblique impact. Six outcomes of drop impact were identified: deposition, prompt splash, corona-corona splash, corona-prompt splash, single-side splash and the aerodynamic breakup. The velocity of the splashing jets and the asymmetric spreading radii were measured from video. The mass-loss coefficient was measured for the drop impact on horizontal targets.