Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session BL: Free Surface Flows II |
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Chair: Andrew Bernoff, Harvey Mudd College Room: Hilton Chicago Astoria |
Sunday, November 20, 2005 10:56AM - 11:09AM |
BL.00001: Rotating fluid bells Nikos Savva, John W.M. Bush We present the results of a combined experimental and theoretical investigation of rotating fluid sheets. When a fluid jet issues downwards from a circular nozzle rotating at sufficient speed, the fluid is deflected into bell-shaped forms whose shapes are prescribed by the balance of inertial, gravitational and curvature forces. We examine the dependence of the flow structure on the governing parameters, and present the results of supporting theoretical developments. [Preview Abstract] |
Sunday, November 20, 2005 11:09AM - 11:22AM |
BL.00002: Folding fluid curtains Esther Wertz, Julien Dervaux, Neil Ribe, Yves Gamblin A sheet or ``curtain'' of viscous fluid falling onto a surface forms a pile of regular folds. Using silicone oil falling through a slot at the base of a reservoir, we have performed laboratory experiments to determine how the folding amplitude and frequency depend on the slot geometry, the fall height, the flow rate, and the fluid properties. A scaling analysis of the data that corrects for the surface tension-induced narrowing of the curtain shows that folding can occur in two limiting regimes. At low heights, ``gravitational'' folding occurs in which the viscous forces that resist folding are balanced by gravity. At great heights, the viscous forces are balanced by inertia (``inertial'' folding). At intermediate heights, we observe a transitional regime characterized by frequency multiplicity and hysteresis effects. We interpret these results in terms of the eigenmodes of an oscillating moment-free liquid sheet that is strongly stretched by gravity. We will also present a simple numerical model for the shape of the narrowing curtain, and compare its predictions with our observations. [Preview Abstract] |
Sunday, November 20, 2005 11:22AM - 11:35AM |
BL.00003: Liquid interfaces in viscous straining flows: numerical studies of the selective withdrawal transition Wendy Zhang, Marko Kleine Berkenbusch, Itai Cohen In selective withdrawal, the interface between two liquid layers is pulled apart by an imposed withdrawal flow. The shape transition creates a sharp hump on the interface, with the minimum hump radius of curvature far smaller than the characteristic lateral length-scale. Previous measurements [Cohen \& Nagel Phys. Rev. Lett. 2002] on equal-viscosity layers suggest the sharp hump is created via an approach towards a steady-state singular shape which is cut off at a small length-scale. In contrast, an analogous shape transition in drop emulsification has been shown to occur via a saddle-node bifurcation, without an approach towards a singular shape. Here we present a numerical model of the selective withdrawal experiment and examine the dynamics near the transition with higher resolution. Our numerical results are consistent with previous measurements, but the increased resolution enables us to identify the shape transition as a saddle-node bifurcation. The transition does not involve approach towards a singular shape. (We thank Sidney R. Nagel for helpful discussions.) [Preview Abstract] |
Sunday, November 20, 2005 11:35AM - 11:48AM |
BL.00004: Spout States in the Selective Withdrawal System Sarah Case, Sidney Nagel, Kimberly Walker In the selective withdrawal experiment, fluid is withdrawn, at rate Q, through a tube with its tip suspended a distance S above an unperturbed interface separating two immiscible fluids. For low Q only the upper fluid is withdrawn, and when Q is increased, or S is decreased, the interface undergoes a transition, and a spout of the lower fluid is entrained in the upper one. For a viscosity ratio of the two fluids $\lambda = \nu_{lower}/\nu_{upper} > 1 $, we have observed that two distinct spout states exist. These are differentiated by their profiles as well as by the flows in the lower fluid. We have also categorized the shapes and flow patterns for systems with $\lambda < 1 $. We also quantify the relationship of the spout width at the entry to the tube as a function of S and Q. This measurement can have impact on diverse applications, such as coating small particles [1]. [1] I. Cohen, et al., Science 292, 265-267 (2001); J. Wyman, et al., (to be published) [Preview Abstract] |
Sunday, November 20, 2005 11:48AM - 12:01PM |
BL.00005: Low Froude number water entry cavity dynamics Jakub K. Kominiarczuk, Dick K.P. Yue We analyze the dynamics of the projectile and the water entry cavity in low Froude number water impact where both kinetic and gravitational potential energy play a role. An experimental investigation is conducted where the impact and cavity development of billiard balls hitting a calm water surface at Froude number of O(10) are captured using high speed video camera at 1000 to 2000 frames per second. The phenomena associated with water entry at low impact speeds are complex as gravity, cavity pressure, flow separation, and splash generation significantly influence the cavity shape, surface closure and pinch off. For comparison, an existing analytical theory for the dynamics of water entry cavities for very high speeds is generalized and extended to low Froude number regime. In particular, this closed-form solution now accounts for effects of gravity and flow separation around the projectile. The comparison between the analytic solution and experimental results is excellent. [Preview Abstract] |
Sunday, November 20, 2005 12:01PM - 12:14PM |
BL.00006: Plouf Christophe Clanet, Virginie Duclaux, Francois Caille Plouf is the noise made by the impact of a solid sphere into a pool when air is entrained. In fact, this impact does not always entrained air and our first point is to address the criterion of entrainement. When air is entrained, a cavity is created the dynamics of which can be described by a Rayleigh-Plesset approach. We show that an algebric equation exists to describe the dynamic of this cavity up to the pinching. [Preview Abstract] |
Sunday, November 20, 2005 12:14PM - 12:27PM |
BL.00007: Run-up created by an advancing surface-piercing cylindrical structure Kenneth Kalumuck, Alan Brandt, Stephen Scorpio, Joseph Hopkins A translating surface piercing object produces a plume of liquid that runs up its face and wraps around its sides before rolling over and breaking up as spray. Results of experiments conducted at various scales with vertical cylinders of circular and faired cross-sections advancing in salt water are presented. Experiments were conducted in both laboratory and large outdoor towing tanks. Results were recorded with video and still photography. The run-up height was found to scale with Froude number, Fr, based on cylinder diameter and consistent with results in the literature at smaller scales. It is also within 80{\%} of theoretical values. The envelope of the side plume was seen to follow a simple ballistic trajectory. Run-up height was found to be unaffected by surfactant addition and introduction of step changes in cylinder width along its vertical extent at or near the free surface. Oscillation of the run-up height was observed to develop as Fr increased. [Preview Abstract] |
Sunday, November 20, 2005 12:27PM - 12:40PM |
BL.00008: On the nature of the Landau-Levich transition Giles Delon, Jacco Snoeijer, Bruno Andreotti, Marc Fermigier A solid plate can be wetted dynamically by a non-wetting liquid when withdrawn from a bath above a threshold velocity. Landau and Levich described long ago the scaling relation giving the thickness of the entrained film. However the nature of the transition from a static meniscus to the Landau-Levich remained unclear. We demonstrate experimentally and theoretically that liquid entrainment occurs due to the nucleation of a solitary wave, well below the critical point corresponding to the disappearance of stationary meniscus solutions. It has been suggested by Golestanian and Raphael that the dynamically forced wetting transition is critical with diverging time scales. This critical behavior is actually avoided by the development of the remarkable ridge-like front that does not trivially match to the liquid reservoir. The macroscopic properties of this ridge are governed by stress balance at molecular scale, and provide a novel, sensitive probe to unravel the singularity at the contact line. [Preview Abstract] |
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