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 KS: Mini-Symposium V: Lagrangain Dynamics in Turbulence |
Hide Abstracts |
Chair: Lance Collins, Cornell University Room: Salt Palace Convention Center Ballroom EG |
Tuesday, November 20, 2007 8:00AM - 8:26AM |
KS.00001: Turbulence in atmospheric clouds Invited Speaker: Atmospheric clouds, a crucial piece of the climate change problem, are almost iconic as visualizations of turbulence. Some of the many aspects of turbulence interacting with cloud particles and radiation fields will be reviewed: from inhomogeneous mixing, to inertial clustering, to stochastic coalescence. The fundamental role of the Lagrangian viewpoint in the cloud-particle coalescence problem will be discussed in the context of a toy model of stochastic rain formation. This provides a context for discussing the emerging recognition of the dominant role of fluctuations in cloud processes. [Preview Abstract] |
Tuesday, November 20, 2007 8:26AM - 8:52AM |
KS.00002: Lagrangian measurements of inertial particle accelerations in turbulent flows. Invited Speaker: Fluid turbulence exhibits strong intermittency at the small scales: the probability of high amplitude fluctuations, caused by intense regions of local vorticity is greatly increased from what would be predicted if the fluctuations had a~Gaussian distribution. This results in the acceleration probability density function (pdf) of passive fluid particles having~highly~stretched exponential tails.~ Particles with density greater than that of the surrounding fluid, i.e., inertial particles, will respond to the flow differently than passive fluid particles. They will be ejected from the intense, intermittent high vorticity regions into regions of high strain, thereby preferentially sampling the flow. This has consequences for raindrop formation in clouds, industrial mixing, dispersion and pollution, and also provides insight into the fluid structure itself. Here we review recent experimental measurements of inertial particles in turbulence. We show that as inertial effects become more pronounced, the tails of the acceleration pdf become less stretched, and that clustering occurs at the small scales. We present measurements of the radial distribution function, a statistical measure of clustering, and relate this to the changes we observe in the acceleration pdf. Results of wind-tunnel experiments are compared with measurements from stirred tanks and ``box turbulence'' and related to direct numerical simulations and models. Effects of particle size and initial flow conditions will be discussed. [Preview Abstract] |
Tuesday, November 20, 2007 8:52AM - 9:18AM |
KS.00003: Lagrangian Structure Functions in Turbulence: Experimental and Numerical Results Invited Speaker: A detailed comparison between experimental and numerical data of Lagrangian velocity structure functions in turbulent flows is presented. Thanks to the integration of information coming from experimental and numerical data, a quantitative understanding of the velocity scaling properties over a wide range of time scales and Reynolds numbers can be achieved. Intermittency changes if measured close to the Kolmogorov time scales or at larger time lags. A quantitative comparison with prediction from multifractal theory for Lagrangian turbulence will also be presented. These results shed some new insight on the relevance of vortex filaments for the statistics of tracers and/or heavy/light particles in turbulence. [Preview Abstract] |
Tuesday, November 20, 2007 9:18AM - 9:44AM |
KS.00004: Imaging-Based Lagrangian Particle Tracking: A Tutorial Invited Speaker: Over the past ten years, there has been an explosive growth in the analysis of turbulent flows in the Lagrangian frame of reference. This is driven in large part by new capabilities in tracking particles in turbulent flows at high Reynolds numbers. Among the particle tracking techniques successfully implemented, imaging-based Lagrangian particle tracking is the most extensively used and provides the highest resolution and the most detailed Lagrangian data of particles in turbulence. Imaging-based particle tracking uses stereoscopic views of particle motions in turbulent flows to reconstruct the 3D trajectories. The most significant challenge is with obtaining the necessary (sub-Kolmogorov) spatial and temporal accuracy to resolve the fastest events in the flow (e.g., large particle accelerations). In this talk, I will review methods we have used to track single- and multiple-particle trajectories in three spatial dimensions and time, including detection of particles based on photo-diode arrays, silicon strip detectors, and ultra-fast CMOS cameras. I will describe in detail the image processing steps to obtain Lagrangian information, including the evaluation and suppression of the effect of noise in the measurement. I will also discuss a new strategy we have developed to dramatically extend particle trajectories by reconstructing trajectory fragments in the images. [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