Destabilization of flapping sheets: The surprising analogue of soap films

When punctured, a uniform liquid sheet is known, since Taylor and Culick, to recess at a constant speed, balancing surface tension and inertia. For planar soap films, this steady solution holds until the initially smooth receding rim is violently destabilized, exhibiting deep indentations from which droplets are ejected. A surprising new three-dimensional mechanism explaining this destabilization and resulting wavelength has been demonstrated: because of the shear between the still outer medium and the receding liquid, the film flaps through a Kelvin-Helmholtz instability, itself inducing an acceleration perpendicular to the film, which intensifies with the flapping amplitude. To this acceleration is associated a classical Rayleigh-Taylor mechanism, promoting the rim indentations. To cite this article: H. Lhuissier, E. Villermaux, C R. Mecanique 337 (2009). (C) 2009 Published by Elsevier Masson SAS on behalf of Academie des sciences.