Liquid jet eruption from hollow relaxation

A cavity hollowed out on a free liquid surface is relaxing, forming an intense liquid jet. Using a model experiment where a short air pulse sculpts an initial large crater, we depict the different stages in the gravitational cavity collapse and in the jet formation. Prior eversion, all cavity profiles are found to exhibit a shape similarity. Following hollow relaxation, a universal scaling law establishing an unexpected relation between the jet eruption velocity, the initial cavity geometry and the liquid viscosity is evidenced experimentally. On further analysing the jet forms we demonstrate that the stretched liquid jet also presents shape similarity. Considering that the jet shape is a signature of the initial flow focusing, we elaborate a simple model capturing the key features of the erupting jet velocity scaling

Relaxation d'interface et jet gravitaire

L'éclatement d'une bulle (Duchemin et al.,2002), l'effondrement d'une cavité suite à une excitation de Faraday (Zeff et al., 2000) ou à la chute d'un objet dans un liquide (Gekle et al., 2010), l'évolution d'une cavité créée au sein d'une goutte après un impact sur une surface hydrophobe (Bartolo et al., 2006) ou la relaxation de longues bulles évoluant dans un liquide visqueux (Séon et Antkowiak, 2012) sont autant de phénomènes physiques où des jets de liquides se manifestent. Ces jets trouvent leurs origines dans les forces d'inertie, de capillarité ou de gravité. De nombreuses études ont porté sur l'évolution des profils de cavités juste avant la création du jet mais peu d'entre elles se sont penchées sur la dynamique de ces jets. Afin d'approfondir les connaissances concernant la dynamique des jets gravitaires, nous avons mis en place une expérience permettant d'obtenir des jets dus à la relaxation de cavités centimétriques à la surface de liquides visqueux. Pour réaliser de telles cavités, une brève impulsion d'air comprimé est appliquée à quelque dizaines de centimètres au dessus de la surface du liquide, ce qui crée une cavité à sa surface. Notre montage expérimental permet de faire varier la largeur et la profondeur de la cavité facilement et la gamme de viscosité du liquide utilisé balaye trois ordres de grandeur. La cavité obtenue relaxe ensuite sous l'influence de la gravité et un jet de liquide émerge alors de celle-ci. Grâce à des moyens en imagerie ultra-rapide, la dynamique de ces jets a été caractérisée. Celle-ci est remarquable car bien que ce phénomène soit gravitaire, le nombre de Froude n'est pas constant. Dans un second temps, le rôle de la viscosité sur la dynamique sera étudié

Large bubble rupture sparks fast liquid jet

This Letter presents the novel experimental observation of long and narrow jets shooting out in disconnecting large elongated bubbles. We investigate this phenomenon by carrying out experiments with various viscosities, surface tensions, densities and nozzle radii. We propose a universal scaling law for the jet velocity, which unexpectedly involves the bubble height to the power 3/2. This anomalous exponent suggests an energy focusing phenomenon. We demonstrate experimentally that this focusing is purely gravity-driven and independent of the pinch-off singularity

Du mélange turbulent aux courants de gravité en géométrie confinée

The present experimental work studies mixing between fluids of different density by buoyancy induced flow in the confined geometry of a tilted tube. The front velocity variations as a function of the control parameters (density contrast \Delta\rho/\rho<Ce travail expérimental analyse le mélange de deux fluides miscibles associé à un écoulement induit par gravité dans la géométrie confinée d'un tube incliné. L'étude de la vitesse du front en fonction des paramètres de contrôle (contraste de densité entre les fluides \Delta\rho/\rho

Solidification dynamic of an impacted drop

17 pages, 6 figuresInternational audienceThis paper is dedicated to the solidification of a water drop impacting a cold solid surface. In a first part, we establish a 1D solidification model, derived from the Stefan problem, that aims at predicting the freezing dynamic of a liquid on a cold substrate, taking into account the thermal properties of this substrate. This model is then experimentally validated through a 1D solidification setup, using different liquids and substrates. In a second part, we show that during the actual drop spreading, a thin layer of ice develops between the water and the substrate, and pins the contact line at its edge when the drop reaches its maximal diameter. The liquid film then remains still on its ice and keeps freezing. This configuration lasts until the contact line eventually depins and the liquid film retracts on the ice. We measure and interpret this crucial time of freezing during which the main ice layer is built. Finally, we compare our 1D model prediction to the thickness of this ice pancake and we find a very good agreement. This allows us to provide a general expression for the frozen drop main thickness, using the drop impact and liquid parameters

Freezing-damped impact of a water drop

We experimentally investigate the effect of freezing on the spreading of a water drop. Whenever a water drop impacts a cold surface, whose temperature is lower than 0 °C, a thin layer of ice grows during the spreading. This freezing has a notable effect on the impact: at given Reynolds and Weber numbers, we show that lowering the surface temperature reduces the drop maximal extent. Using an analogy between this ice layer and the viscous boundary layer, which also grows during the spreading, we are able to model the effect of freezing as an effective viscosity. The scaling laws designed for viscous drop impact can therefore be applied to such a solidification problem, avoiding the recourse to a full and complex modelling of the thermal dynamics

Retraction and freezing of a water film on ice

International audienceWe investigate experimentally the different shapes taken by a water drop freezing during its impact on a cold surface. We show that these shapes are formed by a water film that remains on top of the first formed ice layer. The capillary hydrodynamics of this water film dewetting on its own ice, coupled with its vertical solidification, is thus quantitatively characterized, allowing us to understand and predict the formation of the emerging patterns. Finally, this experiment enables us to study the contact angle dynamics, giving deep insight into the wetting of water on ice