Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session G4: General Fluid Dynamics: Obstacles, Flow Constrictions, Channels |
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Chair: Srinivas Kosaraju, Northern Arizona University Room: 103 |
Monday, November 23, 2015 8:00AM - 8:13AM |
G4.00001: Effect of Local Junction Losses in the Optimization of T-shaped Flow Channels Srinivas Kosaraju T-shaped channels are extensively used in flow distribution applications such as irrigation, chemical dispersion, gas pipelines and space heating and cooling. The geometry of T-shaped channels can be optimized to reduce the overall pressure drop in stem and branch sections. Results of such optimizations are in the form of geometric parameters such as the length and diameter ratios of the stem and branch sections. The traditional approach of this optimization accounts for the pressure drop across the stem and branch sections, however, ignores the pressure drop in the T-junction. In this paper, we conduct geometry optimization while including the effect of local junction losses in laminar flows. From the results, we are able to identify a non-dimensional parameter that can be used to predict the optimal geometric configurations. This parameter can also be used to identify the conditions in which the local junction losses can be ignored during the optimization. [Preview Abstract] |
Monday, November 23, 2015 8:13AM - 8:26AM |
G4.00002: Wakes from submerged obstacles in an open channel flow Geoffrey B. Smith, George Marmorino, Charles Dong, W. D. Miller, Richard Mied Wakes from several submerged obstacles are examined via airborne remote sensing. The primary focus will be bathymetric features in the tidal Potomac river south of Washington, DC, but others may be included as well. In the Potomac the water depth is nominally 10 m with an obstacle height of 8 m, or 80\% of the depth. Infrared imagery of the water surface reveals thermal structure suitable both for interpretation of the coherent structures and for estimating surface currents. A novel image processing technique is used to generate two independent scenes with a known time offset from a single overpass from the infrared imagery, suitable for velocity estimation. Color imagery of the suspended sediment also shows suitable texture. Both the 'mountain wave' regime and a traditional turbulent wake are observed, depending on flow conditions. Results are validated with \textit{in-situ} ADCP transects. A computational model is used to further interpret the results. [Preview Abstract] |
Monday, November 23, 2015 8:26AM - 8:39AM |
G4.00003: The effect of a large upstream bluff body on the flow through and around an array of cylinders Christian Klettner Risers from the sea floor to installations at the sea surface are an integral part of the flow assurance of deep sea oil exploration, which has become necessary in the last decade. These risers are subjected to various hydrodynamic forcing, particularly sea currents, wakes of upstream installation members and surface waves, which can result in vortex or wake induced vibrations and these in turn can result in riser fatigue or collision. The free stream flow past groups of cylinders has been studied numerically in two- and three-dimensions for $Re \sim O(10^3)$ (based on the cylinder diameter) by Nicolle \& Eames (2011) (direct numerical simulations) and Chang \& Constantinescu (2015) (large eddy simulations) respectively. In this study we will be focusing on the first two aspects listed above, specifically laboratory experiments and high resolution numerical simulations will be performed to investigate the effect of an upstream truss on an array of cylinders. The main diagnostic will be how varying the void fraction of the array of cylinders affects the frequency and magnitude of the drag and lift forces on the cylinders. [Preview Abstract] |
Monday, November 23, 2015 8:39AM - 8:52AM |
G4.00004: Optimal design of artificial reefs for sturgeon Cody Yarbrough, Aline Cotel, Abby Kleinheksel The Detroit River, part of a busy corridor between Lakes Huron and Erie, was extensively modified to create deep shipping channels, resulting in a loss of spawning habitat for lake sturgeon and other native fish (Caswell et al. 2004, Bennion and Manny 2011). Under the U.S.-- Canada Great Lakes Water Quality Agreement, there are remediation plans to construct fish spawning reefs to help with historic habitat losses and degraded fish populations, specifically sturgeon. To determine optimal reef design, experimental work has been undertaken. Different sizes and shapes of reefs are tested for a given set of physical conditions, such as flow depth and flow velocity, matching the relevant dimensionless parameters dominating the flow physics. The physical conditions are matched with the natural conditions encountered in the Detroit River. Using Particle Image Velocimetry, Acoustic Doppler Velocimetry and dye studies, flow structures, vorticity and velocity gradients at selected locations have been identified and quantified to allow comparison with field observations and numerical model results. Preliminary results are helping identify the design features to be implemented in the next phase of reef construction. [Preview Abstract] |
Monday, November 23, 2015 8:52AM - 9:05AM |
G4.00005: Physics in water slides Jean-Baptiste Thomazo, Etienne Reyssat, Marc Fermigier Water slides are body-size inclined pipes fed with water to improve sliding. Water is allowed to freely flow down the slide. It forms a lubrication film that reduces friction between the slide and the body, allowing sliders to travel down at high speeds. We present the results of an experimental study on a model water slide at the scale of the laboratory. We analyze the sliding velocities of cylindrical objects of various masses and sizes sliding down an inclined gutter fed with a controlled flux of water. In the range of parameters that we have studied, we show that the speed of the model sliders is faster than the flow of the environing water. We propose a minimal model to account for the observed sliding velocities measured in our experiments. The sliding velocity is set by a balance of the apparent weight with inertial drag or viscous friction in the lubrication film under the slider. Other resisting mechanisms will also be discussed. [Preview Abstract] |
Monday, November 23, 2015 9:05AM - 9:18AM |
G4.00006: Direct Numerical Simulation of two superposed viscous fluids in a rough channel: effect of the position of the interface Isnardo Arenas, Stefano Leonardi Direct Numerical Simulations of two superposed fluids in a turbulent channel with cavities on one wall have been performed. Three different cases have been considered with either square cavities, longitudinal riblets or staggered cubes on the lower wall, the upper wall being smooth. Two viscosity ratios between the two fluids have been used, $m=0.1$ (a fluid of lower viscosity inside the cavities), and $m=10$. The interface between the two fluids is flat mimicking the case of an infinite surface tension. The Reynolds number based on the bulk velocity is $Re=2,800$ and it corresponds to a turbulent Reynolds number $Re_\tau=180$ when both walls are smooth. The height is approximately $h^+=9$. The position of the interface between the two fluids has been varied in the vertical direction. Two cases have been considered, one where interface is above the crests plane, and one where the interface is below the crests plane. When a thin film of low viscosity fluid is above the crests, the stagnation point on the leading edge of the roughness elements moves upward and the form drag decreases thus leading to a drag reduction of up to $30\%$. Drag reduction can be achieved even for $m>1$ due to the damping of wall normal velocity fluctuations. [Preview Abstract] |
Monday, November 23, 2015 9:18AM - 9:31AM |
G4.00007: Geometric Skewness in the Passive Tracer Problem Manuchehr Aminian, Francesca Bernardi, Roberto Camassa, Richard McLaughlin The classic work by G.I. Taylor describes the enhanced longitudinal diffusivity of a passive tracer in laminar pipe flow. Much work since then has gone into extending this result particularly in calculating the evolution of the scalar variance. However, less work has been done to describe the asymmetry of the distribution. We present the results from a modeling effort for the general picture of how the higher moments of the tracer distribution depend on geometry. We do this via analysis of ``channel-limiting" geometries (rectangular ducts and elliptical pipes parameterized by their aspect ratio), using both new analytical tools and Monte-Carlo simulation, which have revealed a wealth of nontrivial behavior of the distributions at short and intermediate time. [Preview Abstract] |
Monday, November 23, 2015 9:31AM - 9:44AM |
G4.00008: Experimental Analysis of the Diffusion of a Passive Scalar Subject to Steady Flow in a Circular Pipe Francesca Bernardi, Manuchehr Aminian, Sarah Burnett, Roberto Camassa, Richard McLaughlin The Taylor Pipe Flow experiment at UNC's Joint Fluids Lab was designed to be a continuation of the research on the dispersion of soluble matter through a tube conducted by G.I. Taylor in the '50s. We explore analytically, numerically and experimentally the evolution of the dispersion of a solute, focusing primarily on computing and measuring the first four moments (mean, variance, skewness and kurtosis) of solute concentration in two-dimensional channel models and three-dimensional glass pipes with circular or square cross-sections. Our experimental setup allows us to observe the effects of Poiseuille flow as either advection or diffusion dominates in different regimes and timescales set by the Taylor time scale $ t_T \propto a^2/\kappa$, depending on the cross-sectional characteristic length $a$ and the diffusion coefficient $\kappa$. We conduct experiments to illustrate these regimes, characterized by the dimensionless P\'{e}clet number, $Pe = u \,a /\kappa$, where $u$ is the characteristic velocity. Experimentally, we take the intensity of a fluorescein-dyed portion of distilled water and find its corresponding concentration by solving an inverse problem of intensity to concentration. The experimental results validate the theoretical approach. [Preview Abstract] |
Monday, November 23, 2015 9:44AM - 9:57AM |
G4.00009: Experimental Investigation of Spatially-Periodic Scalar Patterns in an Inline Mixer Ozge Baskan, Michel F. M. Speetjens, Herman J. H. Clercx Spatially persisting patterns with exponentially decaying intensities form during the downstream evolution of passive scalars in three-dimensional (3D) spatially periodic flows due to the coupled effect of the chaotic nature of the flow and the diffusivity of the material. This has been investigated in many computational and theoretical studies on 3D spatially-periodic flow fields. However, in the limit of zero-diffusivity, the evolution of the scalar fields results in more detailed structures that can only be captured by experiments due to limitations in the computational tools. Our study employs the-state-of-the-art experimental methods to analyze the evolution of 3D advective scalar field in a representative inline mixer, called Quatro static mixer. The experimental setup consists of an optically accessible test section with transparent internal elements, accommodating a pressure-driven pipe flow and equipped with 3D Laser-Induced Fluorescence. The results reveal that the continuous process of stretching and folding of material creates finer structures as the flow progresses, which is an indicator of chaotic advection and the experiments outperform the simulations by revealing far greater level of detail. [Preview Abstract] |
Monday, November 23, 2015 9:57AM - 10:10AM |
G4.00010: Asymptotic scalings of developing curved pipe flow Jesse Ault, Kevin Chen, Howard Stone Asymptotic velocity and pressure scalings are identified for the developing curved pipe flow problem in the limit of small pipe curvature and high Reynolds numbers. The continuity and Navier-Stokes equations in toroidal coordinates are linearized about Dean's analytical curved pipe flow solution (Dean 1927). Applying appropriate scaling arguments to the perturbation pressure and velocity components and taking the limits of small curvature and large Reynolds number yields a set of governing equations and boundary conditions for the perturbations, independent of any Reynolds number and pipe curvature dependence. Direct numerical simulations are used to confirm these scaling arguments. Fully developed straight pipe flow is simulated entering a curved pipe section for a range of Reynolds numbers and pipe-to-curvature radius ratios. The maximum values of the axial and secondary velocity perturbation components along with the maximum value of the pressure perturbation are plotted along the curved pipe section. The results collapse when the scaling arguments are applied. The numerically solved decay of the velocity perturbation is also used to determine the entrance/development lengths for the curved pipe flows, which are shown to scale linearly with the Reynolds number. [Preview Abstract] |
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