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 A9: Interfacial/Thin Film Instability I |
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Chair: Thomas Ward, North Carolina State University Room: 25B |
Sunday, November 18, 2012 8:00AM - 8:13AM |
A9.00001: Gas-driven displacement of a non-Newtonian liquid in a radial Hele-Shaw cell Andrew White, Thomas Ward The displacement of a non-Newtonian liquid by a less viscous fluid has applications in a number of industries such as lubricating oils, injection molding and cement placement in oil wells to name a few. A convenient geometry to study such a problem is that of the Hele-Shaw cell due to its ability to effectively reduce the flow to two dimensions when the gap spacing is much smaller than the other spatial dimensions. We will study the radial displacement of a finite drop of non-Newtonian shear-thinning and extensionally-thickening liquid by a gas at constant pressure in a Hele-Shaw cell with gap spacing O(10-100) microns. Different concentrations of a polymer in oil will be used to examine changes in the displacement rate, residual film thickness and resulting Saffman-Taylor instability as the viscoelastic time scale overtakes that of the bulk displacement. [Preview Abstract] |
Sunday, November 18, 2012 8:13AM - 8:26AM |
A9.00002: Wave Structure and Velocity Profiles in Downwards Gas-Liquid Annular Flows Ivan Zadrazil, Geoff Hewitt, Omar Matar, Christos Markides A downwards flow of gas in the core of a vertical pipe, and of liquid in the annulus between the pipe wall and the gas phase is referred to as a ``downwards annular flow'' (DAF). DAFs are conventionally described in terms of short-lived, small-amplitude ``ripples,'' and large-amplitude, high-speed ``disturbances.'' We use a combination of Laser Induced Fluorescence (LIF), Particle Image and Tracking Velocimetry (PIV, PTV) to study DAFs. We demonstrate through these techniques that the liquid films become progressively more complex with increasing liquid Reynolds number (ReL), while a similar increase of complexity is observed for increasing gas Reynolds number (ReG). Disturbance waves are observed for low and high ReL, and ripples for intermediate ReL. Additionally, a high degree of rolling breakdown of disturbance waves is observed in falling films at the highest ReL, which is a source of bubble entrainment into the film body. Our results will comprise: (i) statistical data on film thickness, and (ii) wave frequency, velocity, wavelength. In addition, a qualitative (e.g. re-circulation zones) and quantitative (e.g. mean/rms velocity profiles) velocity characterisation of the film flows will be presented. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:39AM |
A9.00003: Wave structure in Upwards Gas-Liquid Annular Flows Yujie Zhao, Geoff Hewitt, Omar Matar, Christos Markides A two-phase flow system in a vertical pipe in which the liquid around the pipe periphery is lifted by the gas core is referred to as an ``upwards annular flow'' (UAF). UAFs have a complex interfacial structure, which consists of short-lived, small-amplitude ``ripple'' waves, and large amplitude, high-speed ``disturbances'' waves. Two sets of flush-mounted electrically conducting probes together with axial view photography were used to study UAFs. The overall wave frequency decreased with increasing distance from the inlet until saturation. Disturbance waves were observed over a wide range (both low and high) of liquid Reynolds numbers, ReL, while ripples were observed at lower ReL. Disturbance ``bursts,'' which are a source of liquid entrainment into the gas core, were also observed, with increasing frequency at progressively higher ReL. The waves appeared more chaotic near the inlet, which hindered the formation of the correlated waves. As the small (ripple) waves coalesced into bigger waves with increasing distance from the inlet, the waves became more coherent around the pipe periphery. The results that will be presented comprise: (i) statistical film thickness data, and (ii) wave, frequency, velocity, and wavelength. [Preview Abstract] |
Sunday, November 18, 2012 8:39AM - 8:52AM |
A9.00004: Viscous liquid thin-film flow inside a tube H. Reed Ogrosky, Roberto Camassa, M.G. Forest, Chris Joy, Jeeho Kim, Jeffrey Olander Experiments are conducted over a range of parameters where a high-viscosity silicone oil is fed into the top of a vertical thin glass tube. The oil flows at a continuous rate and the resulting gravity-driven flow coats the inside of the tube. Interfacial instabilities develop due to surface tension and azimuthal curvature. Depending on the experimental parameters, the instabilities either saturate and propagate down the tube as traveling waves or form propagating plugs or liquid bridges. Using a long-wave asymptotic model, we compare the growth rates and phase speed predicted by linear stability analysis with those of the experiments, and the fully nonlinear form of the model is used to predict the formation of plugs. Comparison of the model and experiments to its counterpart exterior setup of a gravity-driven film flow coating a fiber will be mentioned. The experiments are then extended to include pressure-driven airflow at a constant flow rate upwards through the center of the tube. The interfacial stress created by the airflow alters the speed and growth rates of the instabilities. The leading-order effects of the airflow are included in the long-wave model, and a comparison is made once again between model and experiments. [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:05AM |
A9.00005: Reconstruction of a Slippery Undulated bottom Substrate for a thin film flow over it with a Prescribed Spatially Periodic Free Surface Usha Ranganathan A gravity-driven film flow on a slippery undulated inclined substrate is considered. The inverse problem of finding the topography of the bottom slippery substrate for a specific free surface shape which is evolved for flow over it is investigated. Applying the Energy Integral Method, evolution equations for the flow rate and the film thickness are obtained. The influence of slip coefficient, film thickness, inertia and surface tension on the shape of the slippery substrate is examined by prescribing the free surface of the flow over it as a mono frequent periodic function. The contour of the slippery undulated bottom substrate is obtained analytically for weakly undulated free surface. The results of the numerical simulations reveal that the slippery bottom substrate may become strongly nonlinear. The linear stability of the corresponding direct problem is examined and the critical Reynolds number for the flow with a fixed undulated free surface is found to be strongly influenced by surface tension. [Preview Abstract] |
Sunday, November 18, 2012 9:05AM - 9:18AM |
A9.00006: Dynamics of turbulent falling films Lennon O'Naraigh, Omar Matar The dynamics of laminar falling films have received considerable attention over the past several decades. In contrast, turbulent falling films have been the subject of far fewer studies. We seek to redress this balance by studying the stability of falling films which have already undergone a transition from a laminar to a turbulent flow regime. We derive a uniform-film base-state for this flow by assuming the averaged turbulent velocity field to be steady and fully-developed, and by employing a modified version of mixing-length theory. The latter features an interpolation function for the eddy viscosity, and van Driest-type functions for turbulence-damping near the wall and interface regions. The predicted base-state streamwise velocity component is in good agreement with experimental data. A linear stability analysis of this base-state is then carried out by solving a modified version of the Orr-Sommerfeld equation. Our results suggest that the unstable mode is a long-wave one. This provides motivation for the derivation of long-wave equations for the nonlinear evolution of the film. [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:31AM |
A9.00007: Linear stability of a liquid film on a slipping surface with nonuniform slip length Elizaveta Gatapova, Vladimir Ajaev, Oleg Kabov We consider stability of a uniform liquid film on a structured surface. The effect of structuring is modeled by periodic spatial variations of slip length, motivated by a situation when gas-liquid or liquid-liquid menisci form between the elements of the structure. The film instability is driven by disjoining pressure which is modeled by body force terms in the Navier-Stokes equations. Previous investigations of this configuration were based on lubrication-type models, which fail when localized regions of rapid change in surface properties are present, e.g. near the lines of contact between fluid menisci and solid surface. We develop a linear stability theory which is free from the limitations of the lubrication-type approach. Destabilizing effect of the surface structuring is found. The results are compared with the case of uniformly slipping surface. [Preview Abstract] |
Sunday, November 18, 2012 9:31AM - 9:44AM |
A9.00008: On the instability of a circular hydraulic jump Hamid Ait Abderrahmane, Aslan Kasimov We present results of an experimental investigation of symmetry breaking of a circular hydraulic jump observed when a vertical jet of fluid impinges on a horizontal plate. Instabilities break the axial symmetry of the circular jump into quasi-steady polygonal patterns. In between, there exist irregular and unsteady asymmetric jumps. The dynamics of these patterns is recorded experimentally and analysed subsequently by Fourier spectral methods. The attractors that depict the dynamics of are reconstructed and analyzed with the aid of delay and nonlinear time series analysis methods. [Preview Abstract] |
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