Fracture of a viscous liquid

When a viscous liquid hits a pool of liquid of same nature, the impact region is hollowed by the shock. Its bottom becomes extremely sharp if increasing the impact velocity, and we report that the curvature at that place increases exponentially with the flow velocity, in agreement with a theory by Jeong and Moffatt. Such a law defines a characteristic velocity for the collapse of the tip, which explains both the cusp-like shape of this region, and the instability of the cusp if increasing (slightly) the impact velocity. Then, a film of the upper phase is entrained inside the pool. We characterize the critical velocity of entrainment of this phase and compare our results with recent predictions by Eggers

Gravitational oscillations of a liquid column

We report gravity oscillations of a liquid column partially immersed in a bath of liquid. We stress in particular some peculiarities of this system, namely (i) the fact that the mass of this oscillator constantly changes with time; (ii) the singular character of the beginning of the rise, for which the mass of the oscillator is zero; (iii) the sources of dissipation in this system, which is found to be dominated at low viscosity by the entrance (or exit) effects, leading to a long-range damping of the oscillations. We conclude with some qualitative description of a second-order phenomenon, namely the eruption of a jet at the beginning of the rise.Comment: 22 pages, pdf. Submitted to Physics of Fluid

Interfaces en grande déformation (oscillations, impacts, singularités)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Drops impacting a sieve

International audienc

Pointes liquides

Nous décrivons ici ce qui se passe lorsqu’un liquide visqueux est amené à se rencontrer lui-même, comme quand on verse de l’huile dans un verre qui en contient déjà, ou quand on bat des œufs en neige. Si l’impact n’est pas trop violent, on fabrique à l’endroit de la rencontre des liquides une zone remarquable, parfaitement pointue à l’œil nu. Si le choc est plus fort, ces pointes montrent leur fragilité en cédant : de l’air est entraîné avec le liquide en mouvement, conduisant à la formation d’une mousse