Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session M30: General Fluids II |
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Chair: Peter Schmid, LadHyX, Ecole Polytechnique Room: 33A |
Tuesday, November 20, 2012 8:00AM - 8:13AM |
M30.00001: ABSTRACT WITHDRAWN |
Tuesday, November 20, 2012 8:13AM - 8:26AM |
M30.00002: Wetting and partiually wetting rivulets: the role of Reynolds number and boundary conditions Peter Vorobieff, Nima Fathi, Vakhtang Putkaradze, Keith Mertens The behavior of gravity-driven rivulets flowing down an inclined plane or confined between two vertical planes has attracted considerable recent attention. We present a study of several fluids with different wetting properties in both of these arrangements, and discuss the effects of changes in the boundary conditions and the flow rate (both in terms of average Reynolds number and variability). Our experimental arrangement allows to introduce or eliminate fluctuations in the discharge that drives the rivulet, which leads to changes in the flow patterns we observe, including transitions between different flow regimes. For the case of the flow between two vertical planes, one of these regimes manifested for a partially wetting stream exhibits particularly interesting and visually striking features. [Preview Abstract] |
Tuesday, November 20, 2012 8:26AM - 8:39AM |
M30.00003: Measurements of longitudinal surface waves in a soluble surfactant solution N. Washuta, X. Liu, G.M. Korenowski, J.H. Duncan Longitudinal wave trains generated at a surfactant-laden air-water interface are studied experimentally. The experiments are performed in a glass tank that is 75~cm long, 17.8~cm wide, and 4.5~cm deep. Longitudinal waves are generated using a Teflon barrier that spans the width of the tank and oscillates horizontally in the long direction of the tank. The local instantaneous surfactant concentration is measured non-intrusively using a nonlinear optical method called Second Harmonic Generation (SHG). In this method, a laser pulse with a wavelength of 532~nm is reflected off of the free surface at an incident angle of 60 degrees. Due to nonlinear optical effects, the reflected beam contains light with wavelengths of both 532~nm and its second harmonic, 266~nm. The ratio of the intensity of the 266-nm light to the 532-nm light is proportional to the concentration of surfactant on the surface. By measuring the local surfactant concentration versus time at a number of distances from the oscillating barrier, the wavelengths of the longitudinal waves are determined. The relationship between the surface dynamic properties of the surfactant and the measured dispersion relationship of the longitudinal waves is discussed. [Preview Abstract] |
Tuesday, November 20, 2012 8:39AM - 8:52AM |
M30.00004: Water wave metamaterials Philippe Petitjeans, Carmen Palacios, Agn\`es Maurel, Vincent Pagneux The phenomenon of water wave deviation in a bended wave-guide has been studied experimentally. We propose a theoretical analogy to electromagnetism, from which we derive the mathematical tools to design a water wave-deviator. To obtain the effect of metamaterial in the case of surface waves, one has to design a water-bed consisting of periodic layers of two different heights inclined with a specific angle with respect to the direction of propagation of waves. We designed and built (using rapid prototyping) deviators with progressively increasing angles of bending, and their homologue wave-guides with a flat bottom. The wave elevation was measured with good accuracy in time and in space by an optical method. Results show a good efficiency of the wave-deviator. The wavefront maintains its original inclination once the wave crosses the bend (in contrary to the wave-guide with a flat bottom), however departs from the predicted behavior as the wavefront advances. The analysis of harmonics shows a reduction of backwards reflection and a strong decrease in higher modes excitation after the bend. The results are optimistic and might open new possibilities; ultimately those regarding the cloaking of floating structures which could, in the future, be used for coastal protection. [Preview Abstract] |
Tuesday, November 20, 2012 8:52AM - 9:05AM |
M30.00005: Bouncy Fluid Jets Navish Wadhwa, Sunghwan Jung, Pavlos Vlachos Contrary to intuition, free f\mbox{}luid jets can sometimes ``bounce'' of\mbox{}f each other upon collision, due to an entrained air f\mbox{}ilm that keeps them separated. So far, there have only been a few descriptive studies of bouncing jets, since the f\mbox{}irst recorded observation by Rayleigh more than a century ago. We present a quantitative investigation of non-coalescence in jets of same f\mbox{}luid upon an oblique collision. Using a simple experimental set-up, we carried out a parametric study of the bouncing jets by varying the jet diameter, velocity, angle of inclination and f\mbox{}luid viscosity. Our results reveal a scaling law for the contact time of bouncing jets. We further investigate the transition of colliding jets from non-coalescence to coalescence, which seems to be caused by instability of the f\mbox{}luid interface. A dimensionless parameter, which is a function of the Normal Weber Number, Normal Reynolds Number and the angle of inclination of the jets, quantitatively dictates the transition. [Preview Abstract] |
Tuesday, November 20, 2012 9:05AM - 9:18AM |
M30.00006: Hydrodynamic Mass of Bluff Bodies with a Cavity Mohamed Elgabaili, Kenneth Desabrais, Hamid Johari Hydrodynamic mass of an object may be used to compute the contribution of unsteady drag resulting from potential flow. Even though the hydrodynamic mass of certain bluff bodies such as cylinder and sphere have been available from analytical considerations for a long time, there are no analytical solutions for a general bluff body with a cavity such as a cup facing the flow or a round parachute canopy. There is, however, an analytical solution for spherical shells of various concavities. The translational hydrodynamic mass of cups having various depth and thickness as well as round parachute canopies during inflation was computed using a finite element solver. The kinetic energy of the potential flow around the body was used to extract the hydrodynamic mass. Results indicate that the hydrodynamic mass of a cup can be decomposed into two components, the hydrodynamic mass of a cylinder whose axis is aligned with the flow and the mass of fluid within the cup cavity. Similarly, the hydrodynamic mass of a parachute canopy during various stages of inflation may be written as the hydrodynamic mass of a disk having the same area as the projected area of the canopy plus the mass of fluid enclosed by the canopy. [Preview Abstract] |
Tuesday, November 20, 2012 9:18AM - 9:31AM |
M30.00007: Explosion cavities Adrien Benusiglio, Christophe Clanet, David Quere We study the cavities produced at the water-air interface by the explosion of firecrackers. Without confinement, we first observe a spherical hole which grows and reaches a maximal size that depends on the initial energy. Beyond this maximal extension, the cavity collapses in an anisotropic way and leads to the formation of a jet right at the point of explosion. In the case of a confined explosion in a cylindrical tube, the water/air interface initially moves away from the explosion location and reaches a maximal depth that again depends on the initial energy of the explosion. The main difference with the unconfined limit is the fact that the size of the cavity cannot be larger than the size of the confining tube. [Preview Abstract] |
Tuesday, November 20, 2012 9:31AM - 9:44AM |
M30.00008: Rarefied gas correction for the bubble entrapment singularity in drop impacts Laurent Duchemin, Christophe Josserand We study the non-continuous correction in the dynamics of drop impact on a solid substrate. Close to impact, a thin film of gas is formed beneath the drop so that the local Knudsen number is of order one. We consider the first correction to the dynamics which consists of allowing slip of the gas along the substrate and the interface. We focus on the singular dynamics of entrapment that can be seen when surface tension and liquid viscosity can be neglected. There we show that different dynamical regimes are present that tend to lower the singularity strength. We finally suggest how these effects might be connected to the influence of the gas pressure in the impact dynamics observed in recent experiments. [Preview Abstract] |
Tuesday, November 20, 2012 9:44AM - 9:57AM |
M30.00009: The meandering instability of a partial wetting rivulet St\'ephanie Couvreur, Adrian Daerr When a liquid rivulet flows down an inclined plate in partial wetting conditions, it can takes different kinds of shapes. For small flow speed rates, the rivulet flows down the gravity direction, straight along the steepest slope. When increasing the flow rate, an instability leads to the growth of curves and the rivulet finally adopts a sinuous stationary shape, we call this the meandering regime. The rivulet bends grow from defects of the contact line: when the liquid flows along a small perturbation, it is submitted to an inertial centrifugal force which tends to move it to the exterior side of the small curve. Below the instability threshold this force merely distorts the rivulet cross section away from its symetric circular shape at rest, but the contact line remains pinned.When increasing the speed of the liquid (by increasing the flow rate), the inertial effect becomes higher and higher, increasing the external contact angle, until it reaches its critical value, whereupon the rivulet moves and the instability grows. We will show experiments that the critical flow rate depends strongly on the geometry of the initial rivulet. We will explain this dependency through a force balance model, in quantitative agreement with our experiments. S. Couvreur and A. Daerr, EPL, 2012 [Preview Abstract] |
Tuesday, November 20, 2012 9:57AM - 10:10AM |
M30.00010: Sparsity-promoting Dynamic Mode Decomposition Mihailo Jovanovic, Peter Schmid Dynamic mode decomposition (DMD) represents an effective means for capturing the essential features of numerically or experimentally generated flow fields. In order to strike a balance between the quality of approximation (in the least-squares sense) and the number of modes that are used to approximate the given fields, we develop a sparsity-promoting version of the standard DMD algorithm. This is achieved by combining tools and ideas from convex optimization and the emerging area of compressive sensing. Several examples of flow fields resulting from simulations and experiments are used to illustrate the effectiveness of the developed method. [Preview Abstract] |
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