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of occurrence of ice-related incidents in order to maintain public confidence in air
transport.
1.2 Structure of the Thesis
The goal of this study is to improve the understanding on drop splash in the
SLD condition. The impact of supercooled drops in an aircraft icing event has
several specialties. The single drop impact is a frequent occurrence in the in-flight
icing condition. The drops have a particular diameter ranging from 100 µm to
400 µm, and the impact speed is very high, of the order of 100m/s. Furthermore,
the droplets are supercooled, i.e. below 0 ◦ C, but still liquid.
Complete realization of all the impact conditions in the laboratory is very challenging
and might not be necessary. Two experiments were conducted. The first
experiment was to examine the influence of supercooling on the hydrodynamics of
the drop impact process. If the influence is negligible, the high-speed impact can
be conducted at room temperatures. The second experiment is single drop impact
on dry surfaces of various inclinations with high impact speeds, experimentally
investigating oblique drop splash.
Following this introduction, Chapter 2 delivers a literature review on the involved
three topics. The first is the characteristics of the SLD condition. The findings of
meteorological investigations conducted in the past 20 years was summarized in order
to find out the MVD distribution, typical values of the LWC, the most frequent
icing temperatures, and the distribution of icing cloud. This information defines
the impact conditions which are expected to be realized in the experiments, such
as the drop diameter, the impact velocity, the impact angle and the properties of
the impact surface (i.e. dry or wet). The second part is related to drop impact on
dry surfaces. Semi-empirical correlations on the splash threshold was summarized,
and the state-of-art understanding of the physics of splash is reviewed. Current
experimental results on the oblique impact, and the high-speed impact are introduced.
The third part is devoted to the solidification process, including the classical
Stefan problem, which are frequently used in the rest chapters for analyses, and the
experimental and theoretical investigations on the nucleation and the first stage of
solidification, which were specific to the supercooling. This chapter serves as a
starting point of the analysis in the subsequent chapters.
The following four chapters are divided into two parts, respectively describing
the two experiments. Part I, including Chapter 3 and 4, describes the experiment
on the impact of supercooled water drops. Chapter 3 introduces the experimental
setup. In order to acquire supercooled drops of millimeter sizes, a supercooling
4 1. Introduction