Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session LU: Cyberfluids and Industrial Applications |
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Chair: William W. Schultz, National Science Foundation. Room: 204B |
Monday, November 24, 2008 3:35PM - 3:48PM |
LU.00001: An update on turbulence simulations at high core counts P.K. Yeung, D.A. Donzis, D. Pekurovsky Advances in computing power towards the Petascale via systems comprising $O(10^4)$ processor cores (and more) are creating great opportunities as well as substantial challenges for computational science, including direct numerical simulations of turbulence covering a wide range of scales in time and space. We present performance benchmarking data and discuss future optimization strategies for a code based on a highly scalable domain decomposition that allows up to $N^2$ cores on an $N^3$ periodic domain. Very favorable performance results have been achieved on new ``Track 2'' systems supported by NSF, up to $N=8192$ on 32768 cores and over a range of parameters including the choice of Cartesian processor-grid geometry for a given hardware configuration. Both strong scaling (increasing core count for fixed problem size) and weak scaling (core count varied in proportion to problem size) have been assessed in detail. The new algorithms are currently deployed in simulations at $4096^3$ resolution to achieve higher Reynolds number and to resolve the small scales better as suggested by recent literature. Plans for extension to more complex geometries and for sharing both data and codes with the wider Cyber-Fluid Dynamics community will be briefly addressed. [Preview Abstract] |
Monday, November 24, 2008 3:48PM - 4:01PM |
LU.00002: Analysis of isotropic turbulence using a public database and the Web service model, and applications to study subgrid models Charles Meneveau, Yunke Yang, Eric Perlman, Minpin Wan, Randal Burns, Alex Szalay, Shiyi Chen, Gregory Eyink A public database system archiving a direct numerical simulation (DNS) data set of isotropic, forced turbulence is used for studying basic turbulence dynamics. The data set consists of the DNS output on 1024-cubed spatial points and 1024 time-samples spanning about one large-scale turn-over timescale. This complete space-time history of turbulence is accessible to users remotely through an interface that is based on the Web-services model (see http://turbulence.pha.jhu.edu). Users may write and execute analysis programs on their host computers, while the programs make subroutine-like calls that request desired parts of the data over the network. The architecture of the database is briefly explained, as are some of the new functions such as Lagrangian particle tracking and spatial box-filtering. These tools are used to evaluate and compare subgrid stresses and models. [Preview Abstract] |
Monday, November 24, 2008 4:01PM - 4:14PM |
LU.00003: Open source PIV software applied to streaming, time-resolved PIV data Zachary Taylor, Roi Gurka, Alex Liberzon, Gregory Kopp The data handling requirements for time resolved PIV data have increased substantially in recent years as the advent in high speed imaging and real time streaming. Therefore, there is a need for new hardware and software solutions for data storage and analysis. The presented solution is based on open source software (OSS) which has proven to be a successful means of development. This includes the PIV algorithms and flow analysis software. The solution, based on OSS known as ``URAPIV,'' originally was developed in Matlab and recently available in Python. The advantage of these scripting languages lies within their highly customizable platform; however, their routines cannot compete with commercially available software for computational speed. Thus, an effort has been undertaken to develop URAPIV-C++, a GUI based on the Qt 4 cross-platform open source library. This provides users with features commonly found in commercial packages and is comparable in processing speed to the commercial packages. The uniqueness of this package is in its complete handling of PIV experiments from the algorithms to post analysis under OSS license for large data sets. The package and its features are utilized in the recent STR-PIV system, which will be operable at the Advanced Facility for Avian Research at UWO. The wake flow behind an elongated body will be presented as a demonstration. [Preview Abstract] |
Monday, November 24, 2008 4:14PM - 4:27PM |
LU.00004: The Process of Polymer-Turbulence Interactions leading to Polymer Drag Reduction James Brasseur, Ashish Robert, T. Vaithianathan, Lance Collins In a previous study we showed that the statistical properties of polymer drag reduction (DR) in the equilibrium state are found in homogeneous turbulent shear flow (HTSF) with the FENE-P model. We concluded that DR results fundamentally from an interaction among mean shear, turbulence, and polymer molecules. Here we develop insight into the mechanisms that suppress drag by analyzing the activation of polymer-turbulence interactions in HTSF and the transition to the equilibrium state as s function of shear Weissenberg number. We show that the initial state of polymer-turbulence interactions is different from equilibrium. Although both states follow from the suppression of smaller-scale turbulence strain-rate fluctuations by polymer stretching, the details depend on the ultimate level of DR. At early times and in the very low DR equilibrium state, DR is a direct consequence of the small-scale energy transfer from turbulence to polymer. At longer times and at higher drag reduction, DR results from the full elimination of the small scales and the restructuring of the remaining large-scale large vorticity by mean shear that statistically manifests as a suppression of slow pressure-strain energy transfer into vertical velocity. MDR is an asymptotic state in which the mean gradient interacts with polymer to maintain turbulence. [Preview Abstract] |
Monday, November 24, 2008 4:27PM - 4:40PM |
LU.00005: Modeling of particle capture by mechanical means in automotive air filters Brad Bailey, Frank Chambers A model was developed to predict the removal of aerosol particles by automotive air filters. Filtration by direct interception, inertial impaction, and diffusion are correlated to dimensionless parameters. A Kuwabara flow field solution corrected for slip is applied to the flow around a single fiber. The contributions of the three filtration mechanisms are combined into a single-fiber efficiency, yielding overall filter performance. The accuracy of the new model is compared to simulated and experimental data of previous authors for two filter media. One medium has a mean fiber diameter of 0.65 $\mu $m and is examined for particle diameters of 0.01 to 1.0 $\mu $m with filter face velocities from 2 to 8 cm/s. A 2.7 $\mu $m diameter medium is considered for particle diameters of 0.1 to 1.0 $\mu $m with face velocities of 10 to 140 cm/s. For both media, the new model is a better predictor of filtration than our previous model. However, the results of the new model agreed more closely with experimental data for the larger-diameter medium for Stokes numbers less than 0.3, suggesting that direct interception and inertial impaction are predicted more accurately. [Preview Abstract] |
Monday, November 24, 2008 4:40PM - 4:53PM |
LU.00006: Transient models of a displacement ventilation (DV) system and an underfloor air distribution (UFAD) system Jong Keun Yu, Paul Linden Transient models of a displacement ventilation (DV) system and an underfloor air distribution (UFAD) system are examined theoretically and experimentally. We consider that a room heated by a single heat source represented as a buoyant plume and cooled with cooling diffusers. The cooling diffusers of DV system are assumed not to produce any appreciable mixing, while those of UFAD system are negatively buoyant jets which can mix warm air down from the upper part of the space. Conserving mass flux and buoyancy flux, the models determine the transient response of the temperatures in the lower occupied zone and the warm upper layer and the height of the interface between the layers. Non-dimensional transient models of DV and UFAD systems are derived by considering two competing time scales, the filling box time (Baines {\&} Turner 1968) which provides a measure for the establishment of the stratification and the replenishment time in which all the air in the enclosure is replaced by supply air. The models are examined by laboratory experiments using a salt-water analogy. The experiments show good agreement with the theoretical predictions for the initial transients in which the heat source and diffusers start simultaneously, and the time-varying heat or cooling loads simulating dynamic thermal responses in a real building. [Preview Abstract] |
Monday, November 24, 2008 4:53PM - 5:06PM |
LU.00007: Application of a 3D Defocusing Particle Image Velocimetry System to a Virtual Impactor for Microscopic Aerosol Particles Alvaro Pantigoso, Wei-Hsin Tien, Dana Dabiri A Defocusing Digital Particle Image Velocimetry (DDPIV) system is used to observe near-wall effects and flow instabilities within a virtual impactor section of an aerodynamic lens concentrator used to concentrate microscopic aerosol particles. The aerodynamic lens concentrator uses air as its main carrier gas which it draws from a small vacuum system. The DDPIV set up includes a 200mm close-up lens and a double pulsed laser used to backlight the field of view. The image volume is 1.76mmx1.32mmx1.83mm. A three-dimensional velocity field is extracted and the results are compared with preliminary CFD findings. [Preview Abstract] |
Monday, November 24, 2008 5:06PM - 5:19PM |
LU.00008: Ocean Renewable Energy Research at U. New Hampshire M. Wosnik, K. Baldwin, C. White, M. Carter, D. Gress, R. Swift, I. Tsukrov, G. Kraft, B. Celikkol The University of New Hampshire (UNH) is strategically positioned to develop and evaluate wave and tidal energy extraction technologies, with much of the required test site infrastructure in place already. Laboratory facilities (wave/tow tanks, flumes, water tunnels) are used to test concept validation models (scale 1:25--100) and design models (scale 1:10--30). The UNH Open Ocean Aquaculture (OOA) site located 1.6 km south of the Isles of Shoals (10 km off shore) and the General Sullivan Bridge testing facility in the Great Bay Estuary are used to test process models (scale 1:3--15) and prototype/demonstration models (scale 1:1-- 4) of wave energy and tidal energy extraction devices, respectively. Both test sites are easily accessible and in close proximity of UNH, with {\em off-the-shelf} availability. The Great Bay Estuary system is one of the most energetic tidally driven estuaries on the East Coast of the U.S. The current at the General Sullivan bridge test facility reliably exceeds four knots over part of the tidal cycle. The OOA site is a ten year old, well established offshore test facility, and is continually serviced by a dedicated research vessel and operations/diving crew. In addition to an overview of the physical resources, results of recent field testing of half- and full-scale hydrokinetic turbines, and an analysis of recent acoustic Doppler surveys of the tidal estuary will be presented. [Preview Abstract] |
Monday, November 24, 2008 5:19PM - 5:32PM |
LU.00009: Optimization of wafer-back pressure profile in chemical mechanical planarization Tian-Shiang Yang, Yao-Chen Wang, Ian Hu In chemical mechanical planarization (CMP), a rotating wafer is pressed facedown against a rotating pad, while a slurry is dragged into the pad--wafer interface to assist in planarizing the wafer surface. Due to stress concentration, the interfacial contact stress near the wafer edge generally is much higher than that near the wafer center, resulting in spatially nonuniform material removal rate and hence imperfect planarity of the wafer surface. Here, integrating theories of fluid film lubrication and two-dimensional contact mechanics, we calculate the interfacial contact stress and slurry pressure distributions. In particular, the possibility of using a multizone wafer-back pressure profile to improve the contact stress uniformity is examined, by studying a practical case. The numerical results indicate that using a two-zone wafer-back pressure profile with optimized zonal sizes and pressures can increase the ``usable'' wafer surface area by as much as 12\%. Using an optimized three- zone wafer-back pressure profile, however, does not much further increase the usable wafer surface area. [Preview Abstract] |
Monday, November 24, 2008 5:32PM - 5:45PM |
LU.00010: ABSTRACT WITHDRAWN |
Monday, November 24, 2008 5:45PM - 5:58PM |
LU.00011: Unsteady 3D flow simulations in cranial arterial tree Leopold Grinberg, Tomer Anor, Joseph Madsen, George Karniadakis High resolution unsteady 3D flow simulations in major cranial arteries have been performed. Two cases were considered: 1) a healthy volunteer with a complete Circle of Willis (CoW); and 2) a patient with hydrocephalus and an incomplete CoW. Computation was performed on 3344 processors of the new half petaflop supercomputer in TACC. Two new numerical approaches were developed and implemented: 1) a new two-level domain decomposition method, which couples continuous and discontinuous Galerkin discretization of the computational domain; and 2) a new type of outflow boundary conditions, which imposes, in an accurate and computationally efficient manner, clinically measured flow rates. In the first simulation, a geometric model of 65 cranial arteries was reconstructed. Our simulation reveals a high degree of asymmetry in the flow at the left and right parts of the CoW and the presence of swirling flow in most of the CoW arteries. In the second simulation, one of the main findings was a high pressure drop at the right anterior communicating artery (PCA). Due to the incompleteness of the CoW and the pressure drop at the PCA, the right internal carotid artery supplies blood to most regions of the brain. [Preview Abstract] |
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