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 E28: Free-Surface Flows III |
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Chair: Neil Ribe, Laboratoire FAST, Orsay Room: 32A |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E28.00001: Bound-state formation in falling liquid films Phuc-Khanh Nguyen, Marc Pradas, Serafim Kalliadasis, Vasilis Bontozoglou Direct numerical simulation shows that the interaction between solitary pulses may give rise to the formation of bound states consisting of two or more pulses separated by well-defined distances and traveling at the same velocity. Stationary pulse couples are studied first. The resulting equilibrium pulse distances compare favorably to theoretical predictions at large and intermediate pulse separations. When the two pulses are closely spaced, the theory becomes increasingly less accurate. Their time-dependent simulations indicate that all initial conditions of large separations lead to a monotonic attraction or repulsion to the stable bound states. However, intermediate range leads to a self-sustained oscillatory variation of the pulse separation distance, with well-defined amplitude and period, and a mean separation coinciding with the stationary distance. Eventually a very close separation causes an explosive repulsion of two pulses toward much larger stable separation. Bound states consisting of three pulses are computed next. The equilibrium separation distances in a symmetric system are similar to predictions based on simple couples. However, in an asymmetric one, they deviate significantly from simple predictions. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E28.00002: Deformation of a Thin Film by a Wall Jet Naima Hammoud, Talal Al-Housseiny, Howard Stone A variety of industrial processes such as jet stripping or jet wiping involve a high speed stream of gas flowing over a liquid film. In this work, we model this kind of situation by considering a thin viscous liquid film, over which a high Reynolds number laminar wall jet (or Glauert jet) is flowing. We study the shape of the thin liquid film, which is deformed due to the shear stress induced by a jet of a low-viscosity fluid. The mechanics of the jet, which is modeled by boundary-layer theory, is coupled to the mechanics of the thin film, which includes the influence of surface tension and buoyancy. We describe the unsteady shape of the film using the lubrication description to derive a nonlinear PDE that is coupled to the Glauert jet via interfacial stresses. For the steady state, we obtain analytical solutions in different asymptotic regimes. We compare our theoretical findings to numerical simulations conducted with the finite volume solver FLUENT. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E28.00003: High spatio-temporal resolution PIV of laminar boundary layer relaxation instability at the free surface of a jet Matthieu Andre, Philippe Bardet In high-speed free surface flows, microscale instabilities can lead to dramatic macroscale effects such as waves, breakup, or air entrainment. The importance of jets in practical applications requires a better understanding of the mechanisms leading to these instabilities. This experimental study focuses on laminar boundary layer relaxation (LBLR) instability. This has received fewer attention than other instabilities due to the small scale, the high Reynolds number and the proximity of an interface. The experiment features a $20.3mm\times146.0mm$ laminar slab wall jet exiting a nozzle into quiescent air (Re=$3.1\times10^4$ to $1.6\times10^5$). The free surface is flat near the nozzle exit then the LBLR leads to 2D capillary waves which can become very steep eventually resulting in primary breakup and air entrainment. The inception and growth of the capillaries are investigated using time-resolved PIV coupled with PLIF to track the free surface. A magnification of 4 allows a spatial and temporal resolution better than 0.1mm and 0.1ms, respectively. These high resolution results show the role of vortices -created by the roll-up of the shear layer below the surface- in the formation of capillaries. Vortices and waves are a coupled system; the waves can sustain, damp, or amplify. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E28.00004: Torricelli's curtain: morphology of horizontal laminar jets under gravity Neil Ribe, Gabriel Paternoster, Marc Rabaud It has been ``known'' since the seventeenth century that a jet of water issuing horizontally from a hole in the side of a bucket describes a parabolic trajectory. However, this bit of canonical fluid mechanical lore is wrong in many cases. Our recent experiments performed on laminar jets issuing from a horizontal tube show that the initially round jet typically evolves into a thin vertical curtain bounded by bulbous rims at its upper and lower extremities. Moreover, injected dye reveals the presence of a recirculating flow with helical streamlines around the jet's axis. To understand this behavior, we formulate an analytical model for the near-orifice structure of the jet in the limit of large Froude number $Fr\equiv \epsilon^{-1}\gg 1$. We find that a recirculating flow is generated by the sinusoidal variation of the nonhydrostatic pressure around cross-sections of the jet at order $\epsilon$, and that deformation of the cross-section occurs at order $\epsilon^2$. We also use the volume-of-fluid code Gerris to study numerically the evolution of the jet's morphology as a function of the Reynolds, Froude and Ohnesorge numbers, and compare the results with our analytical theory and with laboratory experiments. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E28.00005: Spatial Coherence Resonance for Maximizing Self-Organization and Pattern Fidelity in Free Surface Films Sandra Troian, Nan Liu The influence of external modulation on pattern formation can offer significant insight into hydrodynamic behavior and provide an alternate means of optimizing the self-organization process. While temporal modulation has been used to great effect for decades, there has been less emphasis on external spatial forcing as a way of enhancing pattern uniformity. The majority of studies investigated in the context of spatial coherence phenomena have involved systems undergoing pattern formation in 2D. In this talk, we call attention to hydrodynamic instabilities in thin films in which microarray structures emerge spontaneously in 3D with no intrinsic steady states unless film depletion occurs. However, these structures are highly prone to defects and difficult to control over large areas. For this talk, we focus on an example involving the deformation of a free surface nanofilm exposed to a large transverse thermal gradient whose magnitude is spatially modulated near the resonance point. By a combination of weakly nonlinear analysis and numerical simulations, we demonstrate the existence of a spatial coherence regime leading to rapid growth of perfectly uniform microarrays with high pattern fidelity and even denser packing than possible without spatial forcing. [Preview Abstract] |
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