Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session R10: General Fluid Dynamics V |
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Chair: Patrick Weidman, University of Colorado Room: 334 |
Tuesday, November 26, 2013 1:05PM - 1:18PM |
R10.00001: Slippery liquid-infused porous surfaces in fully developed pipe flow Hafeez Sulaimon, Marcus Lee, Leo Hellstr\"om, Brian Rosenberg, Alexander Smits, Marcus Hultmark Slippery liquid-infused porous surfaces (SLIPS) are created by locking a thin layer of viscous lubricating oil into a porous surface that is textured at the micro/nano scale, with resulting omniphobicity. The oil layer lies between the solid boundary and the surrounding flow, with the potential to create a partial-slip condition at the boundary. SLIPS therefore offers a new approach to achieve drag reduction. Here, SLIPS is applied to fully developed pipe flow for Reynolds numbers ranging from $600$ to $1.8 \times 10^5$. The pipe flow facility consists of two test sections, an untreated and a SLIPS treated section, both 32 diameters long. The two test sections are mounted in series, the first preceded by a 120 diameter long untreated developing section and the second preceded by a 60 diameter long SLIPS treated developing section, to ensure fully developed pipe flow. The effects of SLIPS using oils of different viscosity on the flow resistance is quantified by simultaneously measuring and comparing the pressure drop along the untreated and the SLIPS treated test sections. [Preview Abstract] |
Tuesday, November 26, 2013 1:18PM - 1:31PM |
R10.00002: Discharge Coefficients for Irregular Orifices Wade Huebsch, Donald Gray, Greg Thompson, P.J. Spaur The flow of water through an irregular orifice into an air space is of interest as a model for the flow into a submerged tunnel through a rupture of the wall. An experimental study was conducted of the flow though circular and noncircular thin plate orifices. Steady state discharge coefficients (C$_{\mathrm{d}})$ were measured gravimetrically and photographs of the free jets were taken. Contrary to expectations, C$_{\mathrm{d}}$ increased as the shape deviated from a circle: C$_{\mathrm{d}} = $ 0.61 (circle), 0.625 (square), 0.654 (ellipse), and 0.665 (circular-sawtooth). Four irregular orifices had C$_{\mathrm{d}} = $ 0.657 (least irregular), 0.661, 0.685, and 0.704 (most irregular). The discharge coefficient for the circular orifice agreed with classical results. The jet from the square orifice showed evidence of the expected inversion from a square cross section to a cross. For the elliptical orifice, C$_{\mathrm{d}}$ was independent of the smoothness of the orifice edge. Discharge coefficients were also measured for extruded tubes of various lengths having circular and two irregular cross sections. In all cases the flow changed from a free jet to one which filled the tube at a dimensionless tube length of 2. [Preview Abstract] |
Tuesday, November 26, 2013 1:31PM - 1:44PM |
R10.00003: Breaking the Symmetry with Flexible Blades: Part II Julia Cosse, Daegyoum Kim, Lutz Mueller, Morteza Gharib Vertical axis wind turbines use various methods of asymmetry to promote rotation. Historically two main methods were used; rigid blades with complex shapes or walls blocking the wind from passing through the upwind moving half of the rotor. This project has investigated the use of flexibility as a simpler alternative with great success. A model turbine with interchangeable blades was built and tested in a wind tunnel when configured with several blades of different materials. We found that rotation occurred only when the turbine was equipped with the flexible blades. Successful wind tunnel studies motivated field-testing of the turbine. This talk addresses the recent results regarding the flexible bladed wind turbine testing in the fickle wind environment of the Caltech field laboratory for wind energy (FLOWE). This research is supported by the Gordon and Betty Moore foundation. [Preview Abstract] |
Tuesday, November 26, 2013 1:44PM - 1:57PM |
R10.00004: Experimental Investigation of Scalar Patterns in a Spatially Periodic Flow Field Hadi Rajaei, Ozge Baskan, Michel Speetjens, Herman Clercx Spatially persisting patterns that form during the downstream evolution of passive scalars in three-dimensional (3D) spatially periodic flow fields is a fundamental aspect of industrial mixing processes that rely on the static mixing principle. Despite many numerical studies on 3D spatially periodic flow fields, a comprehensive experimental research on the periodic flow field is still scarce. This research focuses on a comparative analysis between laboratory experiments and numerical simulations on the evolution of the periodic flow field and coherent flow structures and concerns the effect of boundary (i.e. inlet) conditions on the periodicity of the flow field in a representative inline mixer consisting of spatially periodic internal elements. The experimental setup is composed of an optically accessible vertical test section with transparent internal elements which is fed by a pressure-driven pipe flow containing tracer particles. The 3D streamlines, hence, the flow field, are measured by 3D Particle-Tracking Velocimetry technique. The streamwise development of the periodicity within few internal elements regardless of the inlet conditions has been proven by preliminary studies. [Preview Abstract] |
Tuesday, November 26, 2013 1:57PM - 2:10PM |
R10.00005: Leaping shampoo glides on a 500-nm-thick lubricating air layer Erqiang Li, Sanghyun Lee, Jeremy Marston, Andrea Bonito, Sigurdur Thoroddsen When a stream of shampoo is fed onto a pool in one's hand, a jet can leap sideways or rebound from the liquid surface in an intriguing phenomenon known as the Kaye effect. Earlier studies have debated whether non-Newtonian effects are the underlying cause of this phenomenon, making the jet glide on top of a shear-thinning liquid layer, or whether an entrained air layer is responsible. Herein we show unambiguously that the jet slides on a lubricating air layer [Lee et al., Phys. Rev. E, 87, 061001 (2013)]. We identify this layer by looking through the pool liquid and observing its rupture into fine micro-bubbles. The resulting micro-bubble sizes suggest that the thickness of this air layer is around 500 nm. This thickness estimate is also supported by the tangential deceleration of the jet during the rebounding, with the shear stress within the thin air layer sufficient for the observed deceleration. Particle tracking within the jet shows uniform velocity, with no pronounced shear, which would be required for shear-thinning effects. The role of the surfactant may primarily be to stabilize the air film. [Preview Abstract] |
Tuesday, November 26, 2013 2:10PM - 2:23PM |
R10.00006: A new effective macroscopic Stokes-Cahn-Hilliard formulation for immiscible fluids in porous structures Markus Schmuck, Marc Pradas, Grigorios Pavliotis, Serafim Kalliadasis Guided by thermodynamic and variational principles we describe mixtures of incompressible fluids in strongly perforated domains with a general class of phase field equations coupled to the Stokes equations. Important applications include subsurface flows, fuel cells, and microfluidics. Starting with a microscopic formulation for heterogenous domains (e.g. a porous medium), represented as the periodic covering of a single reference cell, we rigorously derive effective macroscopic phase field equations under the assumption of periodic flow for large P\'eclet numbers by the multiple scale method with drift and our recently introduced splitting strategy for Ginzburg-Landau/Cahn-Hilliard-type equations [1]. We recover systematically diffusion-dispersion relations (including Taylor-Aris-dispersion) as for classical convection-diffusion problems. Our results provide a convenient computational framework to macroscopically track interfaces in porous media. In view of the well-known versatility of phase field models, our study proposes a promising formulation for many engineering and scientific applications such as multiphase flows in porous media and oil recovery, for instance. \\[4pt] [1] Schmuck, Pradas, Pavliotis, Kalliadasis, 2012. Proc. R. Soc. A 468, 3705 (2012). [Preview Abstract] |
Tuesday, November 26, 2013 2:23PM - 2:36PM |
R10.00007: Spin-down of a rotating air hockey disk Patrick Weidman, Keith Julien We extend the work of Weidman (APS, DFD 2008) on the steady float height of a rotating disk to formulate and solve for the unsteady behavior of spin-down to rest. A similarity reduction of the Navier-Stokes equations reduces the problem to a coupled pair of partial differential equations in space and time. For a disk of fixed radius and density, the PDE's must be solved taking into account constraints imposed by the aerodynamic torque and aerodynamic lift. Thus the full solution for the unsteady azimuthal and axial dynamics of the disk can be obtained for given initial values of disk Reynolds number $R=W\,h/\nu$ and dimensionless disk rotation speed $S = \sqrt{2} \Omega h/W$, where $h$ is the float height, $W$ is the fluid levitation velocity, $\Omega$ is the disk rotation rate, and $\nu$ is the kinematic viscosity of the fluid. Integrations reveal interesting families of solutions when plotted over steady solution curves in $R$-$S$ parameter space and vindicate the quasi-steady spin-down theory reported in earlier work, valid only in a restricted region of parameter space. [Preview Abstract] |
Tuesday, November 26, 2013 2:36PM - 2:49PM |
R10.00008: Experimental Characterization of Inter-channel Mixing Through a Narrow Gap Simo A. Makiharju, Alexander G. Mychkovsky, John R. Buchanan Jr., Kevin J. Hogan, Kirk T. Lowe, Steven L. Ceccio Mixing trough narrow gaps that connect primary flow paths is an important flow process for many thermal-hydraulic applications, such as flow through nuclear reactor rod bundles or heat exchangers. The flow in a narrow gap can exhibit periodic flow structures due to travelling vortices. These flow structures in the gap, as well as any pressure gradient across the gap, have a significant effect on the rate of mixing between the primary flow paths. To investigate such flows in detail, and to develop validation quality data sets for comparison with CFD, we have conducted a canonical inter-channel mixing experiment between two channels, with a (127 mm)$^{2}$ cross-section. The channels were connected by a gap 914.4 mm long in the stream-wise direction and 50.8mm wide in the cross-stream direction. The gap height could be varied from 0 to 50.8 mm. The flow speed in both channels could be independently varied to have Re $=$ (40 to 100) x 10$^{3}$. The integral mixing rates were determined by injecting fluorescent dye into one of the channels well upstream of the test section and by measuring the dye concentration at the channel inlets and outlets. Additionally, the flow fields in the gap and channels were measured with LDV and PIV. [Preview Abstract] |
Tuesday, November 26, 2013 2:49PM - 3:02PM |
R10.00009: Investigations of Flow past Spinning Cylinders Igbal Mehmedagic, Pasquale Carlucci, Liam Buckley, Donald Carlucci, Elias Aljallis, Siva Thangam A subsonic wind tunnel is used to perform experiments on flow past spinning cylinders. The blunt cylinders are sting-mounted and oriented such that their axis of rotation is aligned with the mean flow. The experiments cover a Reynolds number range of up to 300000 and rotation numbers of up to 1.2 (based on cylinder diameter). The results for spinning cylinders with both rear-mounted and fore-mounted stings are presented. Computations are performed using a two-equation anisotropic turbulence model that is based on proper representation of the energy spectrum to capture rotation and curvature. The model performance is validated with benchmark experimental flows and implemented for analyzing the flow configuration used in the experimental study. [Preview Abstract] |
Tuesday, November 26, 2013 3:02PM - 3:15PM |
R10.00010: The High Reynolds Number Limit of Nonlinear Equilibrium States in Couette Flow Kengo Deguchi, Philip Hall In recent years there has been much interest in the nonlinear equilibrium states, which Couette flow can support. Computational interest in this problem began with Nagata in the early 1990's and since then there have been numerous investigations of shear flows. Beginning in the late 1980's Hall and Smith laid down an asymptotic framework, referred to as vortex-wave interaction theory, for nonlinear equilibrium states generated by the interaction of TS or inviscid wave systems in a variety of shear flows. In 2010 Hall and Sherwin showed conclusively that the asymptotic theory described what were referred to in the CFD community as self sustained processes. Subsequently Deguchi, Hall and Walton (2013) showed that the asymptotic states at small wavenumbers took on a new structure capable of describing spot formation. The asymptotic theory was however unable to predict the so-called upper branch self-sustained process found numerically and the theory predicted a critical wavenumber beyond which asymptotic states could not be found. Here the upper branch structure is given in the high Reynolds number limit and the development of asymptotic modes beyond the critical wavenumber is given thereby completing the description of equilibrium states at high Reynolds numbers. [Preview Abstract] |
Tuesday, November 26, 2013 3:15PM - 3:28PM |
R10.00011: Nonlinear Equilibrium States in Growing Boundary Layers Philip Hall, Kengo Deguchi Recently there has been much interest in vortex wave interaction/self sustained process/coherent structures in fully developed flows. In growing boundary layers the local Reynolds number varies in the flow direction and so the relevance of equilibrium states calculated for developed flows is in doubt. Here results are presented for nonlinear states in quite general boundary layers. Some of the structures we find using asymptotic and numerical methods are ``distant cousins'' of structures found in for example Couette flow whilst others are apparently unrelated. The new states are completely dependent on the background state being a boundary layer and are found have an elegant canonical asymptotic form. The new states are shown to be valid for quite general boundary layers; in addition they are related to experimental observations. [Preview Abstract] |
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