Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session KN: General Fluid Dynamics II |
Hide Abstracts |
Chair: M. Koochesfahani, Michigan State University Room: Salt Palace Convention Center 251 B |
Tuesday, November 20, 2007 8:00AM - 8:13AM |
KN.00001: When does the dipole caused by the motion of a two-dimensional body vanish? Stefan Llewellyn Smith, Sebastien Michelin, Darren Crowdy The fluid velocity far from a translating body in two-dimensional irrotational flow is dipolar. This is a classical result. Here we ask when the dipolar component vanishes. Lamb (1945, \S\,\textbf{126}) provides symmetry conditions on the virtual mass tensor for this to be the case. We show that these conditions are not necessary and obtain the sufficient and necessary condition in terms of the shape of the body using conformal maps. The applicability of the condition is discussed. [Preview Abstract] |
Tuesday, November 20, 2007 8:13AM - 8:26AM |
KN.00002: PIV investigation of a shallow wake Arindam Singha, A. Shinneeb, R. Balachandar Shallow wake, generated by shallow flow past a bluff body, has very distinct characteristics different from a conventional deep wake. The presence of the bounding surfaces (bed and free surface) imparts significant three-dimensionality to the flow. Although many wakes encountered in nature and in engineering applications can be classified as shallow, few studies have been carried out to explore this flow. The present study is aimed towards understanding the characteristics of a typical shallow wake using particle image velocimetry (PIV). The shallow wake is generated by a sharp-edged bluff body, placed in a boundary layer type of flow with freestream velocity of 0.19 m/s (Reynolds number based on momentum thickness $\approx $ 735). Measurements are taken at near-bed, mid-depth and near free-surface horizontal planes behind the body. The analysis of the mean velocity field shows drastic effect of the bed as well as free surface. The extent of the wake, as well as the half-width and entrainment characteristics at different horizontal planes clearly show three-dimensionality of the near-wake flow field. Proper orthogonal decomposition technique is also applied to understand the dynamics of the large-scale structures of the shallow wake. [Preview Abstract] |
Tuesday, November 20, 2007 8:26AM - 8:39AM |
KN.00003: Experimental Investigation of Flow in a Cavity with a Porous Opening M. Koochesfahani, S. Rayepalli, R. Gupta The velocity field within a nominally two-dimensional cavity is investigated in a water channel. The Reynolds number based on cavity depth and freestream speed is about 300. The purpose of the study is to characterize the changes in the recirculation flow pattern inside the cavity caused by a porous surface covering the cavity opening. Both flow visualization and quantitative results for the mean and fluctuating velocity field will be discussed for various surfaces of different porosity. [Preview Abstract] |
Tuesday, November 20, 2007 8:39AM - 8:52AM |
KN.00004: Friction laws for planar channels with idealized periodic roughness elements. D. Kasiteropoulou, A. Liakopoulos, T. Karakasidis Laminar 2D and turbulent flows in channels formed by two infinite parallel walls (a smooth lower wall and a rough upper wall) have been studied numerically. Roughness of upper wall is modeled by periodically-spaced rectangular or triangular protruding elements. Laminar flows were studied by Direct Numerical Simulation (DNS) while the Reynolds-averaged Navier-Stokes equations (RANS) were employed for the turbulent flow. The dependence of flow pattern on protrusion type, channel geometry dimensionless parameters, and Reynolds number is investigated. Protrusions promote formation of vortices even at very low Reynolds numbers. An inherently unstable shear layer is formed between the low-speed fluid trapped between adjacent protrusions and the high-speed fluid streaming in the central channel part. The force exerted by the walls on the fluid is larger in the case of rectangular protrusions, at least in the range of Reynolds numbers and protrusion heights studied. The calculated pressure drop is compared with theoretical relations for planar Poiseuille flow and empirical relations for turbulent flows. An effort is also made to determine the validity of laminar flow scaling relations for micro and nano-flows. Acknowledgments: The project is co-funded by the European Union -- European Social Fund {\&} National Resources -- Epeaek II. [Preview Abstract] |
Tuesday, November 20, 2007 8:52AM - 9:05AM |
KN.00005: Bistability and the transition to chaos in a flapping flag model Silas Alben, Michael Shelley We study the nonlinear dynamics of a heavy elastic sheet moving in a 2D inviscid fluid and which sheds a vortex sheet from its trailing edge. Many previous flag models are approximations, with varying degrees of accuracy, to this model. We use the model to characterize the behavior of flapping flags at large amplitudes and over many flapping periods. As bending rigidity is decreased, we find a transition from periodic to chaotic flapping. This transition is characterized by the appearance of higher-wavelength bending modes and smaller flapping frequencies. We also determine the stability boundary of the flow-aligned state for the flag, in the two-dimensional parameter space of dimensionless flag inertia and bending rigidity. We find bistability of flapping and stretched-straight states over a range of dimensionless rigidity, in agreement with experiments. [Preview Abstract] |
Tuesday, November 20, 2007 9:05AM - 9:18AM |
KN.00006: Flow-induced Forces on Two Nearby Circular Cylinders Dong-Hyeog Yoon, Kyung-Soo Yang, Kyongjun Lee Flow-induced forces on two identical nearby circular cylinders immersed in the cross flows below Re=160 were numerically studied using an immersed boundary method. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and, the angle inclined with respect to the main flow direction. It turns out that significant changes in the characteristics of vortex shedding are noticed depending on how the two cylinders are positioned, resulting in quantitative changes of force coefficients on both cylinders. Collecting all the numerical results obtained, we propose contour diagrams for the force coefficients on the distance vs. angle plane for each of the two cylinders. The geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow- induced forces on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction. [Preview Abstract] |
Tuesday, November 20, 2007 9:18AM - 9:31AM |
KN.00007: Flow-induced Forces on Two Nearby Spheres Kyung-Soo Yang, Dong-Hyeog Yoon Flow-induced forces on two identical nearby spheres at Re=300 were numerically studied using an immersed boundary method. We consider all possible arrangements of the two spheres in terms of the distance between the spheres and, the angle inclined with respect to the main flow direction. It turns out that significant changes in the characteristics of vortex shedding are noticed depending on how the two spheres are positioned, resulting in quantitative changes of force coefficients on both spheres. Collecting all the numerical results obtained, we present the diagrams for the force coefficients on the distance vs. angle plane for each of the two spheres. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow-induced forces on two identical spheres arbitrarily positioned in physical space with respect to the main flow direction. [Preview Abstract] |
Tuesday, November 20, 2007 9:31AM - 9:44AM |
KN.00008: Drag Crisis of Gyro-Balls Yoshiyuki Yokoyama, Takeshi Miyazaki, Ryutaro Himeno Using a high-speed video camera, we measured the trajectory and the rotation of a hard baseball thrown by a pitching machine which can launch Gyro-Balls (rifle spinning balls). We determined the drag- and lift- coefficients by analyzing the video images. The measurements were performed in the range of 0.6$\times $10$^{5}<$Re$<$2.5$\times $10$^{5}$, and for three values of the spin parameter (SP : dimensionless spin rate)=0.12,0.23 and 0.35. Two seam patterns relative to the translational direction were investigated, i.e. 2-seam and 4-seam. The drag coefficient of a 4-seam gyro-ball with SP=0.12,0.23 and 0.35, decreases gradually with Re. However, the drag coefficient of a 2-seam gyro-ball with SP=0.12 decreases in two steps, i.e. in the ranges 0.8$\times $10$^{5}<$Re$<$1.0$\times $10$^{5}$ and 2.0$\times $10$^{5}<$Re$<$2.2$\times $10$^{5}$, and attains its minimum at Re=2.2$\times $10$^{5}$. The drag coefficients of a 2-seam Gyro-Ball with SP=0.23,0.35 are almost constant below Re=1.6$\times $10$^{5 }$and Re=1.3$\times $10$^{5}$, respectively. Their minima are attained at Re=1.8$\times $10$^{5}$ and Re=1.6$\times $10$^{5}$, respectively. These findings confirm the occurrence of the drag crisis for Gyro-Balls. The different Re-dependencies are due to the different seam patterns. [Preview Abstract] |
Tuesday, November 20, 2007 9:44AM - 9:57AM |
KN.00009: Innovative method for greatly reducing fluid flow resistance Weiyi Lin In this paper, firstly, the aerated pipe flow experiment is introduced. And some experimental research on comparison between different volume of air entrained is presented. Secondly, the technical characteristics of gravity pipe flow under the action of Torricelli's vacuum, shortly called as GPFUTV are dissertated, including creative and functional design, fundamental principle and the strange energy loss phenomena, etc. The detailed information on energy loss of water flow under GPFUTV's condition please find the attached YongAn Water Plant Test Report Auguest 1997 and ShiLong District Reservoir Diversion Project Test Report April 2007. Thirdly, an appeal in relation to the experimental research, the applied studies and basic theory research is given. For instance, Reynolds' experiment and Nikuradze's experiments under GPFUTV's condition, the use of GPFUTV instead of lifting pump in DOW project and deep ocean mining project, flow stability and flow resistance under GPFUTV's condition, etc. At last, the application of GPFUTV in reservoir release control is is illustrated. [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