Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session A28: Free-Surface Flows I |
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Chair: Julie Crockett, Bringham Young University Room: Spirit of Pittsburgh Ballroom B/C |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A28.00001: Jet impingement and thin film breakup on a superhydrophobic surface Julie Crockett, Joseph Prince, Daniel Maynes A vertical laminar jet impinging on a horizontal surface spreads out in a thin film on the surface. If the surface is hydrophobic, and a downstream depth is not maintained the film will breakup into droplets. This occurs where the jet's outward radial momentum is balanced by the inward surface tension force of the advancing film. An analytical model has been created to estimate this location. All surfaces explored are hydrophobic or superhydrophobic (SH), where the SH surfaces exhibit an apparent slip at the surface. For SH surfaces with random micropatterning, the slip on the surface is uniform in all directions and droplet breakup occurs in a circular pattern. When alternating rib/cavity microstructures are used to create a SH surface the slip varies as a function azimuth resulting in an elliptically shaped breakup. The location of breakup for multiple surfaces over a range of jet Weber numbers and realistic slip length values is determined. Results show the breakup radius increases with increasing Weber number and slip length. The eccentricity of the breakup ellipse for the rib/cavity SH structures increases with increasing Weber number and slip length as well. The model results compare well to experimental measurements. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A28.00002: Absolute and convective instabilities in film flow over inclined topography Dmitri Tseluiko, Mark Blyth, Demetrios Papageorgiou The stability of a liquid film flowing under gravity down an inclined wall with periodic corrugations is analyzed. A long-wave equation valid at near-critical Reynolds numbers is used to study the film dynamics. Steady solution branches are computed including subharmonic branches, for which the period of the free surface is an integer multiple of the wall period, and the existence of quasi-periodic branches is demonstrated. Stability analysis of steady periodic solutions shows that under certain conditions, and depending on the wall period, the flow may be convectively unstable for small wall amplitudes but undergo transition to absolute instability as the wall amplitude increases. The predictions of the linear theory are corroborated by time-dependent simulations of the model equation. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A28.00003: The miscible two-fluid flow down an inclined plane: Linear stability analysis R. Usha, Rama Govindarajan, Outi Tammisola The linear stability of a miscible two-layer free-surface flow of varying viscosity, down an inclined substrate is examined. We show that the stability characteristics are different from both immiscible two-layer flows and continuously stratified flows. A new instability mode, namely overlap mode, absent in either limiting case, arises when the critical layer of the disturbance overlaps the viscosity-stratified layer. At moderate miscibility, the configuration with less viscous fluid adjacent to the inclined plane is most stabilizing. This is also contrast with the limiting cases, in which the lubrication configuration is always destabilizing. The co-existence of several growing overlap modes, the usual surface mode and a Tollmien-Schlichting mode are observed and this presents interesting new possibilities for nonlinear breakdown. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A28.00004: Thin film flow down a porous substrate in the presence of a soluble surfactant: Linear stability analysis Yadav Anjalaiah, R. Usha The linear stability of a thin film flowing down an inclined porous substrate in the presence of soluble surfactants is investigated. A surfactant model in which the surfactant has affinity only for the liquid-gas and not for the liquid-solid interface, and is contained in the bulk only as a monomer is considered. The adsorption-desorption kinetics of the surfactant at the liquid-gas interface is accounted for. An Orr-Sommerfeld eigenvalue problem is formulated and is solved analytically in the limit of long-wave perturbations and numerically for arbitrary wave-length using Spectral-Tau collocation method. The effects of solubility of the surfactant, the characteristics of the porous medium and adsorption-desorption kinetics are examined. The results reveal the stabilizing effect of soluble surfactant on the flow system. It is possible to either stabilize or destabilize the flow system by appropriately choosing the characteristics of the porous medium. The presence of soluble surfactants is shown to be more effective in stabilizing the flow system than that of insoluble surfactants. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A28.00005: Recoil of a liquid filament: escape of the pinch-off by creation of a vortex ring Jerome Hoepffner, Gounseti Pare A liquid filament recoils under the effect of its surface tension. It may recoil to one sphere: the geometrical shape with lowest surface, or otherwise segment to several pieces which individually will recoil to spheres. This experiment is classical and its exploration is fundamental to understanding how liquid volumes relax. In this talk, we uncover a mechanism involving the creation of a vortex ring which plays a central role in escaping the segmentation. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A28.00006: Spinning hydraulic jump Hamid Abderrahmane, Aslan Kasimov We report an experimental observation of a new symmetry breaking of circular hydraulic jump into a self-organized structure that consists of a spinning polygonal jump and logarithmic-spiral waves of fluid elevation downstream. The waves are strikingly similar to spiral density waves in galaxies. The fluid flow exhibits counterparts of salient morphological features of galactic flows, in particular the outflow from the center, jets, circum-nuclear rings, gas inflows toward the galactic center, and vortices. The hydrodynamic instability revealed here may have a counterpart that plays a role in the formation and sustainability of spiral arms in galaxies. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A28.00007: Linear and weakly nonlinear analysis of the rotating polygon instability Jerome Mougel, David Fabre, Tomas Bohr In this talk we will present new analytic results about the polygonal instability obtained in a cylindrical container with rotating bottom [G. H. Vatistas, J. Fluid. Mech, \textbf{217}, 241, (1990), Jansson et al., Phys. Rev. Lett, \textbf{96}, 174502, (2006)]. In a recent study we showed that this spectacular instability can be explained as a result of wave interaction by introducing a simplified model that allows analytical predictions [L. Toph{\o}j et al., Phys. Rev. Lett, \textbf{110}, 194502, (2013)]. Instability maps of the global stability analysis will be presented here, as well as results of the weakly nonlinear analysis performed on the simple model which lead to the amplitude equations of the resonating free surface waves. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A28.00008: Meniscus Stability in Rotating Systems Yvonne Reichel, Michael Dreyer In this study, the stability of free surfaces of fluid between two rotating coaxial, circular disks is examined. Radially mounted baffles are used to form menisci of equal size. To the center of the upper disk, a tube is connected in which a separate meniscus is formed. Assuming solid-body rotation and ignoring dynamic effects, it is observed that the free surfaces between the disks fail to remain stable once the rotation speed exceeds a critical value. In other words, Rayleigh-Taylor instability ensues when the capillary forces fail to balance centrifugal forces. Dimensionless critical rotation speeds are studied by means of the Surface Evolver via SE-FIT for varied number of baffles, the normalized distance between the disks, and the normalized central tube radius. Drop tower tests are performed to confirm some of the numerical results. The computation also reveals that there are different modes of instability as a function of the relevant parameters. [Preview Abstract] |
Sunday, November 24, 2013 9:44AM - 9:57AM |
A28.00009: Hydraulic jumps and contact lines formed by jet impact on an incline Laurent Limat, Alexis Duchesne, Remy Herbaut, Luc Lebon We have investigated the shape and stability of hydraulic jumps formed on an inclined plate, around a jet under normal impingement. We have explored three different wetting conditions: total wetting, partial wetting and super-hydrophobicity. In the first case, a strong departure to axisymmetry of the shape is observed, with often disappearance of the lower part of the jump. One also observes the formation of an effective, curved, static contact line around the jump, with a similar horse-shoe structure. Surprisingly, the effective jump radii defined in the directions normal and parallel to the in plane gravity follow quite well Bohr et al scaling, initially proposed for a horizontal, axisymetric jump, but with prefactors dependant on the plate slope. In the partial wetting case, the coupling between the jump and the contact line makes things more complex and Bohr' scaling seems to hold only at large plate slope. In the super hydrophobic case, the structure is strongly axisymmetrical, and reminiscent of sheet atomization. The sheet radius is governed by a balance between surface tension and momentum, itself moderated by the viscous friction on the plate. [Preview Abstract] |
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