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 E14: General Fluid Dynamics: Drag Reduction |
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Chair: Marc Perlin, University of Michigan Room: 202 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E14.00001: Investigations of Air Perfusion through Porous Media and Super-Hydrophobic Surface Active Gas Replenishment Marc Perlin, James W. Gose, Kevin Golovin, Steven L. Ceccio, Anish Tuteja Super-hydrophobic (SH) materials have been used successfully to generate reduced skin-friction in laminar flows. Success in the laminar regime has led researchers to try SH materials in turbulent flows. More often than not, this has been unsuccessful at providing meaningful skin-friction drag reduction, and has even generated increased drag. This failure is frequently attributed to the wetting of an SH surface or equivalently the transition from the Cassie-Baxter to the Wenzel state. The result is fluid flow over an essentially roughened surface. In this investigation the researchers aim to perfuse small amounts of gas through porous media, including sintered and foam metals, to attain skin-friction drag reduction in a fully-developed turbulent channel flow. As air is perfused through porous media, the solid - liquid interaction at the interface transitions to a solid - liquid - gas interaction. This can result in an interface that functions similarly to SH materials. Controlled air perfusion that provides the necessary replenishment of lost gas at the interface might prevent wetting, and thus eliminate or reduce the effect of the roughness on the flow. This latter possibility is investigated by perfusing small amounts of gas through porous media with and without SH coatings. To quantify the effectiveness of this method, pressure drop is used to infer friction drag along the surface in a fully-developed turbulent channel flow. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E14.00002: A priori models for predicting drag reduction for flow over heterogeneous slip boundaries Margaret Heck, Dimitrios Papavassiliou Slip at fluid-fluid/fluid-solid interfaces is a subject of interest for many engineering applications, ranging from porous materials to biomedical devices to separation processes. Despite remarkable effort to include the effects of surface topology and various flow and physical properties in models describing fluid slip, the mathematical description of flow over mixed slip boundaries is still under investigation. Using similarity theory, which is based on the generalized homogeneity of physical laws governing most systems and takes advantage of similarity in the spatial distribution of characteristics of motion, the equivalent slip velocity is shown to be a function of the geometry of a microfluidic system. The results are used to predict the slip velocity for flow over surfaces with periodically repeating no-slip/free-shear boundaries in the shape of rectangles for 16{\%}-50{\%} solid fractions. The equivalent slip velocity for flow over rectangular boundaries can then be related to the those for flow over surfaces with square and circular no-slip boundaries using characteristic length ratios. The models developed using this apporach can be directly used to estimate the slip velocity for flow over various free-shear/no-slip boundaries for Couette, laminar flow conditions. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E14.00003: Sustained Drag Reduction in Turbulent Taylor-Couette Flows Enabled by Low-Temperature Leidenfrost Effect Dhananjai Saranadhi, Dayong Chen, Justin Kleingartner, Siddarth Srinivasan, Robert Cohen, Gareth McKinley A submerged body can be heated past its Leidenfrost temperature to form a thick, continuous film of steam between itself and the water. Here we employ a superhydrophobic surface to drastically reduce the energy input required to create and sustain such a boiling film, and use the resulting slip boundary condition to achieve skin friction drag reduction on the inner rotor of a bespoke Taylor-Couette apparatus. We find that skin friction can be reduced by over 90{\%} relative to an unheated superhydrophobic surface at \textit{Re}$=$ 19,200, and derive a boundary layer and slip theory to fit the data to a model that calculates a slip length of 3.12 $\pm$ 0.4 mm. This indicates that the boiling film has a thickness of 112 $\mu$m, which is consistent with literature. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E14.00004: Drag reduction over liquid-infused surfaces in turbulent Taylor-Couette flow Tyler Van Buren, Brian Rosenberg, Alexander Smits We present an experimental study on aqueous turbulent flow over a liquid-infused textured surface for the purpose of drag reduction. Taylor-Couette flow experiments are performed over a range of laminar to turbulent conditions (Re $=$ 1500 to 7000), where the skin friction is compared to (i) a baseline case that consists of a textured surface with no impregnated fluid and (ii) an air-impregnated superhydrophic surface. We achieve drag reduction as high as 11{\%} with superhydrophic surfaces and 4{\%} with liquid infused surfaces. Of particular interest in this study is (1) the impact of surface texture shape and gap size on the resulting surface skin friction, (2) the importance of the viscosity ratios of the two fluids and its relationship to drag reduction, and (3) longevity of effectiveness when comparing liquid- to air-infused surfaces. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E14.00005: Drag Coefficient of Thin Flexible Cylinder Chelakara Subramanian, Harika Gurram Measurements of drag coefficients of thin flexible cylindrical wires are described for the Reynolds number range between 250 -- 1000. Results indicate that the coefficient values are about 20 to 30 percent lower than the reported laminar flow values for rigid cylinders. Possible fluid dynamics mechanism causing the reduction in drag will be discussed. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E14.00006: Geometry Mediated Drag Reduction in Taylor-Couette Flows Shabnam Raayai, Gareth McKinley Micro-scale ribbed surfaces have been shown to be able to modify surface properties such as skin friction on both natural and fabricated surfaces. Previous experiments have shown that ribbed surfaces can reduce skin friction in turbulent flow by up to 4-8{\%} in the presence of zero or mild pressure gradients [1]. Our previous computations have shown a substantial reduction in skin friction using micro-scaled ribs of sinusoidal form in high Reynolds number laminar boundary layer flow. The mechanism of this reduction is purely viscous, through a geometrically-controlled retardation of the flow in the grooves of the surface. The drag reduction achieved depends on the ratio of the amplitude to the wavelength of the surface features and can be presented as a function of the wavelength expressed in dimensionless wall units. Here we extend this work, both experimentally and numerically, to consider the effect of similar ribs on steady viscous flow between concentric cylinders (Taylor-Couette flow). For the experimental work, the inner rotating cylinder (rotor) is machined with stream-wise V-groove structures and experiments are performed with fluids of different viscosity to compare the measured frictional torques to the corresponding values on a smooth flat rotor as a measure of drag reduction. The numerical work is performed using the OpenFOAM\textregistered open source software to compare the results and understand the physical mechanisms underlying this drag reduction phenomenon. [1] D. Bechert \textit{et al.}, Experiments in Fluids \textbf{28} (2000) [Preview Abstract] |
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