Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session L9: General Fluid Dynamics: Drag Reduction |
Hide Abstracts |
Chair: Stefano Leonardi, University of Texas, Dallas Room: B117 |
Monday, November 21, 2016 4:30PM - 4:43PM |
L9.00001: Why fibers are better turbulent drag reducing agents than polymers. Arnout Boelens, Murugappan Muthukumar It is typically found in literature that fibers are not as effective as drag reducing agents as polymers. However, for low concentrations, when adding charged polymers to either distilled or salt water, it is found that polymers showing rod-like behavior are better drag reducing agents than polymers showing coil-like behavior [1]. In this study [2], using hybrid Direct Numerical Simulation with Langevin dynamics, a comparison is performed between polymer and fiber stress tensors in turbulent flow. The stress tensors are found to be similar, suggesting a common drag reducing mechanism in the onset regime. Since fibers do not have an elastic backbone, this must be a viscous effect. Analysis of the viscosity tensor reveals that all terms are negligible, except the off-diagonal shear viscosity associated with rotation. Based on this analysis, we are able to explain why charged polymers showing rod-like behavior are better drag reducing agents than polymers showing coil-like behavior. Additionally, we identify the rotational orientation time as the unifying time scale setting a new time criterion for drag reduction by both flexible polymers and rigid fibers. References: [1] P.S. Virk (1975), Nature, 253, 109-110 [2] A.M.P. Boelens, M. Muthukumar (2016), PRE, 93, 052503 [Preview Abstract] |
Monday, November 21, 2016 4:43PM - 4:56PM |
L9.00002: Bubble drag reduction requires large bubbles Ruben Verschoof, Roeland van der Veen, Chao Sun, Detlef Lohse In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. A few volume percent ($\leq 4\%$) of bubbles can reduce the overall drag up to 40\% and beyond. However, the exact mechanism is unknown, thus hindering further progress and optimization. Here we show that bubble drag reduction in turbulent flow {\it dramatically} depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40\% to about 4\%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid . The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow. [Preview Abstract] |
Monday, November 21, 2016 4:56PM - 5:09PM |
L9.00003: Rigid spherical particles in highly turbulent Taylor-Couette flow Dennis Bakhuis, Ruben A. Verschoof, Varghese Mathai, Sander G. Huisman, Detlef Lohse, Chao Sun Many industrial and maritime processes are subject to enormous frictional losses. Reducing these losses even slightly will already lead to large financial and environmental benefits. The understanding of the underlying physical mechanism of frictional drag reduction is still limited, for example, in bubbly drag reduction there is an ongoing debate whether deformability and bubble size are the key parameters. In this experimental study we report high precision torque measurements using rigid non-deformable spherical particles in highly turbulent Taylor-Couette flow with Reynolds numbers up to $2 \times 10^6$. The particles are made of polystyrene with an average density of 1.036 g cm$^{-3}$ and three different diameters: 8mm, 4mm, and 1.5mm. Particle volume fractions of up to 6\% were used. By varying the particle diameter, density ratio of the particles and the working fluid, and volume fraction of the particles, the effect on the torque is compared to the single phase case. These systematic measurements show that adding rigid spherical particles only results in very minor drag reduction. [Preview Abstract] |
Monday, November 21, 2016 5:09PM - 5:22PM |
L9.00004: Liquid Infused Surfaces in Turbulent Channel Flow Matthew Fu, Ying Liu, Howard Stone, Marcus Hultmark Liquid infused surfaces have been proposed as a robust method for turbulent drag reduction. These surfaces consist of functionalized roughness elements wetted with a liquid lubricant that is immiscible with external fluids. The presence of the lubricant creates mobile, fluid-fluid interfaces, each of which can support a localized slip. Collectively, these interfaces yield a finite slip velocity at the effective surface, which has been demonstrated to reduce skin friction drag in turbulent flows. Retention of the lubricant layer is critical to maintaining the drag reduction effect. A turbulent channel-flow facility is used to characterize the drag reduction and robustness of various liquid infused surfaces. Micro-manufactured surfaces are mounted flush in the channel and exposed to turbulent flows. The retention of fluorescent lubricants and pressure drop are monitored to characterize the effects of surface geometry and lubricant properties. [Preview Abstract] |
Monday, November 21, 2016 5:22PM - 5:35PM |
L9.00005: Slip length of liquid-infused surfaces in high aspect-ratio microchannels Arunraj Balaji, Matthew Fu, Marcus Hultmark Liquid-infused surfaces (LIS) derive their drag-reduction effects from the presence of flow inside lubricant-filled surface cavities or grooves. This behavior has been characterized by an effective slip length, which is known to be the primary parameter in determining drag-reduction. Though slip length has been theoretically parametrized as a function of LIS geometry, fluid properties, and channel dimensions, previous studies were performed without consideration of all three variables simultaneously. Specifically, existing models do not address the regime in which channel height is on the order of LIS-feature length scale. High aspect-ratio microchannels with rectangular-groove LIS along one wall are constructed and tested. Pressure measurements are used to determine effective slip length for various surface geometries, channel heights, and viscosity ratios. Results are compared with theoretical expectations. [Preview Abstract] |
Monday, November 21, 2016 5:35PM - 5:48PM |
L9.00006: Optimizing Geometry Mediated Skin Friction Drag on Riblet-Textured Surfaces Shabnam Raayai, Gareth McKinley Micro-scale riblets have been shown to modify the skin friction drag on patterned surfaces. Shark skin is widely known as a natural example of this passive drag reduction mechanism and artificial riblet tapes have been previously used in the America's Cups tournament resulting in a 1987 victory. Previous experiments with riblet surfaces in turbulent boundary layer flow have shown 4-8{\%} reduction in the skin friction drag. Our computations with sinusoidal riblet surfaces in high Reynolds number laminar boundary layer flow and experiments with V-grooves in laminar Taylor-Couette flow also show that the reduction in skin friction can be substantial and depends on the spacing and height of the riblets. In the boundary layer setting, this frictional reduction is also a function of the length of the plate in the flow direction, while in the Taylor Couette setting it depends on the gap size. In the current work, we use scaling arguments and conformal mapping to establish a simplified theory for laminar flow over V-groove riblets and explore the self-similarity of the velocity contours near the patterned surface. We combine these arguments with theoretical and numerical calculations using Matlab and OpenFOAM to show that the drag reduction achievable in laminar flow over riblet surfaces depends on a rescaled form of the Reynolds number combined with the aspect ratio of the texture (defined in terms of the ratio of the height to spacing of the riblets). We then use these results to explain the underlying physical mechanisms driving frictional drag reduction and offer recommendations for designing low drag surfaces. [Preview Abstract] |
Monday, November 21, 2016 5:48PM - 6:01PM |
L9.00007: Development of reduced drag concepts for acoustic liners using experimental methods Christopher Jasinski, Thomas Corke Commercial aircraft have used acoustic liners to reduce engine noise for many years, although their drag production has been largely unstudied. The next generation of aircraft may benefit from additional surface area covered by acoustic liner, thus understanding their drag production mechanism is crucial for future designs. An accurate direct aerodynamic drag measurement technique has been developed using a force balance with linear air bearings. Using 3D-printed and conventional liners, low-drag designs are being developed. This paper will investigate the underlying fluid mechanics governing the drag production in acoustic liners and describe new attempts to reduce aerodynamic drag. [Preview Abstract] |
Monday, November 21, 2016 6:01PM - 6:14PM |
L9.00008: ABSTRACT WITHDRAWN |
Monday, November 21, 2016 6:14PM - 6:27PM |
L9.00009: Vapor layers reduce drag without the crisis Ivan Vakarelski, Joseph Berry, Derek Chan, Sigurdur Thoroddsen The drag of a solid sphere moving in fluid is known to be only a function of the Reynolds number, Re and diminishes rapidly at the drag crisis around Re $\sim $ 3 \texttimes 10$^{\mathrm{5}}$. A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect, can occur over a wide range of Re, from as low as $\sim $ 600. The Navier slip model with a viscosity dependent slip length captures the observed drag reduction and wake shape. [Preview Abstract] |
Monday, November 21, 2016 6:27PM - 6:40PM |
L9.00010: Octopus-inspired drag cancelation by added mass pumping Gabriel Weymouth, Francesco Giorgio-Serchi Recent work has shown that when an immersed body suddenly changes its size, such as a deflating octopus during rapid escape jetting, the body experiences large forces due to the variation of added-mass energy. We extend this line of research by investigating a spring-mass oscillator submerged in quiescent fluid subject to periodic changes in its volume. This system isolates the ability of the added-mass thrust to cancel the bluff body resistance (having no jet flow to confuse the analysis) and moves closer to studying how these effects would work in a sustained propulsion case by studying periodic shape-change instead of a “one-shot” escape maneuver. With a combination of analytical, numerical, and experimental results, we show that the recovery of added-mass kinetic energy can be used to completely cancel the drag of the fluid, driving the onset of sustained oscillations with amplitudes as large as four times the average body radius. Moreover, these results are fairly independent of the details of the shape-change kinematics as long as the Stokes number and shape-change number are large. In addition, the effective pumping frequency range based on parametric oscillator analysis is shown to predict large amplitude response region observed in the numerics and experiments. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700