This thesis provides unique insights into the characteristics and dynamics of millimetre-sized
liquid drops impacting on heated substrates maintained above the Leidenfrost point. Threedimensional
direct numerical simulations are carried out to investigate the Leidenfrost drop
regime. The Level Contour Reconstruction interface hybrid tracking method, which combines
the advantages of the level set and front-tracking methods, is adopted to simulate the complex
three-dimensional phase change flow for which interfacial oscillations are a predominant feature.
Good comparisons are obtained by validating the present numerical framework with experimental
data and numerical results from the literature.
The characteristics and dynamics associated with the different Leidenfrost drop shape regimes
are systematically investigated over a wide range of Bond numbers. The drop shapes are elucidated
beyond the steady state drop shapes previously presented in theoretical [1] and numerical
approaches [2]. Drops with large Bond numbers exhibit more complex dynamics due to the
dominance of the inertial forces over the surface tension forces, while smaller drops remain
quasi-spherical. The role of the vapour layer is investigated, and the effect of the vapour layer
on the base and the emergence of interfacial oscillations is presented. Bubble encapsulation
mechanisms occur at the apex and the base of the drop, with the former shown to occur at
low Weber numbers. Additionally, the effect of the surface temperature on sustained bouncing
brought about by the vapour layer is investigated at low Bond and Weber numbers. The rebound
height largely depends on the surface temperature, and it is found that under-damped bouncing
dynamics are associated with high surface temperatures.
Due to the prominent role of drop impact in many industrial applications, the dynamics of
impacting drops are studied at high Weber numbers. Two jetting mechanisms are highlighted,
and the pressure and temperature profiles show the role of the propagating interfacial waves on
the dynamic transition prior to the jetting singularity. Upward jetting occurs at the early and
late stages of the drop lifetime, while downward jetting occurs during the onset of the recoiling stage. Fingering patterns are observed in sub-cooled drops with more complex dynamics than
saturated drops, and the role of the different instabilities is highlighted.