Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session G16: Free-Surface Flows IV: Instability |
Hide Abstracts |
Chair: Henri Lhuissier, University of Paris Room: 2000 |
Monday, November 24, 2014 8:00AM - 8:13AM |
G16.00001: The effect of noncondensables on thermocapillary-buoyancy convection Tongran Qin, Roman Grigoriev We consider convection in a layer of volatile simple fluid with free surface subject to a horizontal temperature gradient in the presence of noncondensable gases, such as air, and driven by a combination of buoyancy and thermocapillary stresses. At ambient conditions a unicellular base flow becomes unstable as the temperature gradient is increased, developing a multicellular structure. Recent experimental studies showed that the composition of the gas phase has a significant effect on the convection pattern. In particular, although varying the average concentration of noncondensables over an experimentally accessible range has almost no effect on the average flow speed, the transition to multicellular convection is significantly delayed when noncondensables are evacuated. Using a combination of numerical simulations and linear stability analysis which account for heat and mass transport in the gas phase we show that this dependence is due mainly to the changes in thermocapillary stresses which are controlled by the variation in the composition of the gas phase that arises in response to evaporation and condensation. [Preview Abstract] |
Monday, November 24, 2014 8:13AM - 8:26AM |
G16.00002: The effect of noncondensables on the stability of buoyancy-thermocapillary convection Yaofa Li, Roman Grigoriev, Minami Yoda Buoyancy-thermocapillary convection is a well-known problem that is also of interest in evaporative cooling. Our fundamental understanding of convection and transport in the presence of phase change remains limited, however. Pathline visualizations and PIV were used to study convection in a confined layer of a pure volatile 0.65~cSt silicone oil driven by a horizontal temperature gradient at Marangoni numbers $Ma < 10^3$ and Bond numbers $Bo_D = O(1)$ below a sealed vapor space containing noncondensables ({\it i.e.}, air) at concentrations $c_{\rm a} = 11~{\rm mol}\%-96\%$. At $c_{\rm a} = 96$\% ({\it i.e.}, ambient conditions), the results are in qualitative agreement with previous studies and a new linear stability analysis, with transitions from steady unicellular to partial multicellular to steady multicellular flow, then to oscillatory multicellular (OMC) flow as $Ma$ increases. In the OMC state, the cells oscillate near the heated end, but travel instead towards the cooled end. The results show that decreasing $c_{\rm a}$ has a marked effect on the flow stability, increasing the critical $Ma$ for transition between different flow states. Indeed, only steady unicellular and partial multicellular flow states are observed at $c_{\rm a} = 11$\% for these $Ma$. [Preview Abstract] |
Monday, November 24, 2014 8:26AM - 8:39AM |
G16.00003: Two-dimensional Faraday instability with a spatially periodic bottom Nicolas Perinet, Claudio Falcon, Seungwon Shin, Jalel Chergui, Damir Juric We study two-dimensional Faraday waves in a channel with rectangular obstacles on the lower boundary, varying the height and the length of the obstacles as well as the distance separating them to understand their influence on the wave patterns. The analysis is mainly numerical and performed by means of BLUE, a code based on a hybrid Front-Tracking/Level-set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces. In the absence of obstacles, the bifurcation diagram shows three distinct instabilities: the classical instability that leads to the formation of patterns, the sudden onset of temporal chaos and finally a high jump in the amplitude of the waves, the latter bifurcation showing hysteresis. We show that the presence of obstacles delays the primary threshold, inhibits the secondary instabilities and enriches the dynamics of the interface. In particular, obstacles add a new spatial large-scale stationary mode and harmonics resulting from its interaction with the classical resonant modes. [Preview Abstract] |
Monday, November 24, 2014 8:39AM - 8:52AM |
G16.00004: Faraday instability in deformable domains Giuseppe Pucci, Martine Ben Amar, Yves Couder We investigate the Faraday instability in floating liquid lenses, as an example of hydrodynamic instability that develops in a domain with flexible boundaries. We show that a mutual adaptation of the instability pattern and the domain shape occurs, as a result of the competition between the wave radiation pressure and the capillary response of the lens border. Two archetypes of behaviour are observed. In the first, stable shapes are obtained experimentally and predicted theoretically as the exact solutions of a Riccati equation, and they result from the equilibrium between wave radiation pressure and capillarity. In the second, the radiation pressure exceeds the capillary response of the lens border and leads to non-equilibrium behaviours, with breaking into smaller domains that have a complex dynamics including spontaneous propagation. [Preview Abstract] |
Monday, November 24, 2014 8:52AM - 9:05AM |
G16.00005: Instability of the capillary bridge Gounseti Pare, Jerome Hoepffner Capillary adhesion is a physical mechanism that maintains two bodies in contact by capillarity through a liquid ligament. The capillary bridge is an idealization of this capillary adhesion. In this study we first focus on the classical case of the stability of the capillary bridge. Secondly we study a slightly more complex configuration, imagining a flow in the capillary bridge as in the case of the dynamics of the neck of a liquid ligament, in its withdrawal under the effect of capillarity. Inspired by the experiments on soap films of Plateau, the configuration analyzed consists of an initially axisymmetric, mass of fluid held by surface tension forces between two parallel, coaxial, solid pipes of the same diameter. The results presented are obtained by numerical simulations using the free software, Gerris Flow Solver. We first focus on the capillary Venturi. In the static configuration the stability diagram of the capillary bridge obtained is in perfect agreement with the results of Lev A. Slobozhanin. In the dynamic case we develop a matlab code based on the one dimensional equations of Eggers and Dupont. The comparison of the bifurcation diagram obtained and the numerical simulations shows a good agreement. [Preview Abstract] |
Monday, November 24, 2014 9:05AM - 9:18AM |
G16.00006: Stability of an unsupported multi-layer surfactant laden liquid curtain under gravity Dominic Henry, Jamal Uddin, Jeremy Marston, Sigurdur Thoroddsen The industrial process of curtain coating has long been an important method in coating applications, by which a thin liquid curtain is formed to impinge upon a moving substrate, the highly lucrative advantage being able to coat multiple layers simultaneously. We investigate the linear stability of an unsupported two-layer liquid curtain, which has insoluble surfactants in both liquids. We formulate the governing equations, simplified by making a thin film approximation, from which we obtain equations describing the steady state profiles. We then examine the response of the curtain to small perturbations about this steady state to identify conditions under which the curtain is unstable, finding the addition of surfactants stabilizes the curtain. Our results are then compared to experimental data, showing a favourable trend and therefore extending the work of Brown\footnote{D. Brown, \textit{J. Fluid Mech.} \textbf{10}, 297-305 (1960).} and Dyson \textit{et al.}\footnote{R.J. Dyson, J. Brander, C.J.W. Breward and P.D. Powell, \textit{J. Eng. Math.} \textbf{64}, 237-250 (2009).} [Preview Abstract] |
Monday, November 24, 2014 9:18AM - 9:31AM |
G16.00007: Polygons in a Liquid Metal Free Surface Driven by Rotating Permanent Magnets Sergio Cuevas, J. Carlos Dominguez-Lozoya, Michel Rivero, Eduardo Ramos We report the appearance of an instability in a shallow liquid metal layer (GaInSn) driven by different arrays of rotating magnetized bars (6 cm $\times$ 1.27 cm $\times$ 1.27 cm) located at the bottom of a cylindrical plexiglas container with a diameter of 20.32 cm. The thickness of the fluid layer is 0.6 cm and the maximum analyzed rotation frequency is 7 Hz. We explored arrays with one, three, four, and five magnet bars placed radially and equidistantly. For specific magnet rotation frequencies, we observed the spontaneous breaking of the axial symmetry of the free surface which takes the form of an ellipse for the case of one rotating magnet, or a polygon with three, four, or five corners for the cases of three, four or five rotating magnets, respectively. The structures rotate uniformly with a speed about an order of magnitude lower that the rotating magnets. Similarities with instabilities observed with free surface hydrodynamic flows driven by a rotating bottom plate are discussed. [Preview Abstract] |
Monday, November 24, 2014 9:31AM - 9:44AM |
G16.00008: Impact of a viscoelastic jet Henri Lhuissier, Baptiste N\'eel, Laurent Limat A jet of a Newtonian liquid impacting onto a wall at right angle spreads as a thin liquid sheet which preserves the radial symmetry of the jet. We observe that for a viscoelastic jet (solution of polyethylene glycol in water) this symmetry can break: close to the wall, the jet cross-section is faceted and radial steady liquid films (membranes) form, which connect the cross-section vertices to the sheet. The number of membranes increases with increasing viscoelastic relaxation time of the solution, but also with increasing jet velocity and decreasing distance from the jet nozzle to the wall. A mechanism for this surprising destabilization of the jet, which develops perpendicularly to the direction expected for a buckling mechanism, is presented that explains these dependences. The large-scale consequences of the jet destabilization on the sheet spreading and fragmentation, which show through the faceting of hydraulic jumps and suspended (Savart) sheets, will also be discussed. [Preview Abstract] |
Monday, November 24, 2014 9:44AM - 9:57AM |
G16.00009: Experiments and non-parallel theory on the natural break-up of freely falling Newtonian liquid jets Paula Consoli-Lizzi, Wilfried Coenen, Alejandro Sevilla The capillary break-up of liquid jets issuing from a needle at a constant flow rate is studied experimentally and theoretically. In particular, we focus on globally stable jets of a Newtonian liquid that are strongly stretched by gravity, so that the region close to the injector is highly non-parallel. In this regime, the use of parallel linear stability theory, based on a local dispersion relation between the frequency and the wavelength of travelling-wave disturbances, is questionable. We therefore propose a global linear frequency response analysis based on a one-dimensional formulation of the mass and momentum equations. Our model reveals that perturbations present large damping in the initial region of strong axial stretching, followed by a growth that eventually causes the break-up of the jet. Besides the break-up length, our model also allows for the prediction of the most amplified frequency. The theoretical predictions are compared with experimental observations, that comprise the natural break-up of stretched jets for a wide range of liquid viscosities, injector radii and flow rates. [Preview Abstract] |
Monday, November 24, 2014 9:57AM - 10:10AM |
G16.00010: Rill patterning on sloping snowpacks induced by Hortonian runoff Elisa Mantelli, Carlo Camporeale, Luca Ridolfi The morphological instability leading to rill formation over snowpacks is addressed in the present study. First, Hortonian saturation of a surface thin layer of snow is demonstrated to occur during the rising-intensity stage of rainfall events because the velocity of the water wavefront in the unsaturated snow is proportional to rainfall intensity. Therefore, a slowly downward-propagating shockwave is formed, behind which Hortonian saturation eventually occurs, and a turbulent water film moving along the maximum slope direction is allowed to develop above the snowpack surface. The linear stability analysis of the system made up of the water film and the saturated snow layer is then performed, and the dispersion relation obtained analytically. A spanwise morphological instability corresponding to rills is detected and investigated as a function of slope, friction coefficient, Reynolds number and wavenumber. The maximum instability wavelength is shown to have a purely hydrodynamic origin and to be originated by the interplay between pressure perturbation, free surface response and Reynolds stresses. Field work has been also performed, that confirms the validity of the presented model. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2020 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700