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The contact angle between a gas-liquid interface and a solid surface is a function of the dynamic conditions of the contact line. Classic steady correlations link the contact angle to the contact line velocity. However, it is unclear whether they hold in the presence of inertia and the case of perfect wetting fluids. We analyze by means of experiments the shape of a liquid interface and the corresponding contact angle in accelerating conditions for two different fluids, i.e. HFE7200 (perfect wetting) and demineralized water. The set-up consists of a U-shaped quasi-capillary tube in which the liquid column oscillates in response to a pressure step on one of the two sides. We obtained the evolution of the interface shape from high-speed back-light visualization, fit interface models to the experimental data to estimate the contributions of all the governing forces and perform measurements of the dynamic contact angle. We propose a new model to account for the impact of the interface acceleration on its shape, and we discuss the impact on the measurement of the transient contact angle. The new model allows to perform dynamic contact angle measurements below 15 degrees, which is challenging to obtain with traditional techniques. We show for the first time a dynamic characterization of the wetting behavior of HFE7200, and we compare the results with traditional hydrodynamic models.

Sloshing refers to the motion of the free liquid/gas interface inside a partially filled container subjected to an external excitation with a consequent motion of the system center of gravity. Several parameters related to the fluid container, the fluid properties, the excitation levels, and the gravitational environment govern this phenomenon. Moreover, it is a significant cause of disturbance in embarked reservoirs. In this paper, it is shown that the absolute liquid/gas interface position η A during moderate sloshing (i.e., in the absence of splashing and wave breaking) can be measured over the full surface domain by the Reference Image Topography technique. It is applied to sloshing in steady and in transient regimes, underlining its potential.

The measurement of fluid velocity in the vicinity of wavy interfaces by means of Particle Image Velocimetry (PIV) still constitutes a challenge. Besides the experimental complexities such as appropriate seeding, reflections due to gradients in refractive indices, aberrations, etc., also the image processing phase constitutes a critical component. Ignoring bias errors introduced by laser reflections near the interface, strong velocity gradients are typically encountered near the curved liquid/gas interface and are detrimental to the common cross-correlation analysis. These effects are exacerbated by the use of traditional rectangular static cross-correlation windows. More-