Browsing by Author "Drumright-Clarke, M. A."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- The effect of insoluble surfactant at dilute concentration on drop breakup under shear with inertiaDrumright-Clarke, M. A.; Renardy, Yuriko Y. (American Institute of Physics, 2004-01)Direct numerical simulations are conducted with a volume-of-fluid continuous surface stress algorithm. The linear equation of state is used to characterize the effects of an insoluble surfactant at low concentration on a drop in strong shear. The drop and the surrounding liquid have the same viscosity and density. Surfactant migration induces a Marangoni force that acts toward the drop center. For low inertia, viscous force opposes the Marangoni force, so that a stationary drop with surfactant is more elongated and less tilted than without. The addition of surfactant promotes breakup, lowering the critical capillary number. The first daughter drops are smaller than for the case of clean drops. For high inertia, the Marangoni force retracts the drop and retards breakup. The local values of surface tension are computed during drop evolution.
- Pyramidal and toroidal water drops after impact on a solid surfaceRenardy, Yuriko Y.; Popinet, S.; Duchemin, L.; Renardy, Michael J.; Zaleski, S.; Josserand, C.; Drumright-Clarke, M. A.; Richard, D.; Clanet, C.; Quere, D. (Cambridge University Press, 2003-06)Superhydrophobic surfaces generate very high contact angles as a result of their microstructure. The impact of a water drop on such a surface shows unusual features, such as total rebound at low impact speed. We report experimental and numerical investigations of the impact of approximately spherical water drops. The axisymmetric free surface problem, governed by the Navier-Stokes equations, is solved numerically with a front-tracking marker-chain method on a square grid. Experimental observations at moderate velocities and capillary wavelength much less than the initial drop radius show that the drop evolves to a staircase pyramid and eventually to a torus. Our numerical simulations reproduce this effect. The maximal radius obtained in numerical simulations precisely matches the experimental value. However, the large velocity limit has not been reached experimentally or numerically. We discuss several complications that arise at large velocity: swirling motions observed in the cross-section of the toroidal drop and the appearance of a thin film in the centre of the toroidal drop. The numerical results predict the dry-out of this film for sufficiently high Reynolds and Weber numbers. When the drop rebounds, it has a top-heavy shape. In this final stage, the kinetic energy is a small fraction of its initial value.