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Colloquia Archive
Untitled Document
| DATE: |
Friday, April 18th, 2008 |
| TITLE: |
ENERGY CASCADE IN TURBULENT FLOWS; QUANTIFYING EFFECTS OF
LOCAL AND NONLOCAL INTERACTIONS
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| TIME: |
3:30 PM |
| LOCATION: |
GMCS 214 |
| SPEAKER: |
Julian Andrzej Domaradzki
Aerospace and Mechanical Engineering
University of Southern California
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| ABSTRACT: |
The classical Kolmogorov theory of turbulence
is based on the concept of
the energy transfer from larger to progressively smaller scales of motion.
The theory assumes that bulk of the energy transfer in the inertial range
of turbulence occurs between scales of similar size, a process known as
the local energy cascade. The assumed locality allows to postulate that
after multiple cascade steps the small scale dynamics become universal,
i.e., independent of particulars of large scales that are determined by
geometry, boundary conditions, and forces causing a particular flow. Yet
despite its central role in the Kolmogorov theory the locality assumption
cannot be easily verified, neither analytically nor experimentally. This
is because, mathematically, the energy transfer is a result of
interactions among different scales of motion originating from the
nonlinear term in the Navier-Stokes equation that couples all scales.
Relevant questions can be productively addressed using databases generated
in large scale numerical simulations. We describe such databases and use
them to compute detailed energy exchanges between scales of motion with
well defined sizes, obtained by decomposing numerical velocity fields
using banded filters, and investigate how the detailed transfers
contribute to the global quantities such as the classical energy transfer
and the energy flux. The developed procedure allows to quantify locality
of the energy transfer and to address a persistent controversy concerning
the role of nonlocal interactions in this process, i.e., of much larger
scales than those transferring energy. The analysis of detailed
interactions reveals that the individual nonlocal contributions are always
large but significant cancellations lead to the global quantities
asymptotically dominated by the local interactions. Apart from an
intellectual challenge of clarifying these issues, obtained results have
bearing on practical questions of turbulence modeling that will be
addressed in the talk.
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| HOST: |
Guus Jacobs |
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Computational Science Research Center :: 5500 Campanile Drive :: San Diego, CA 92182-1245 :: (619) 594-3430
©2007 Computational Science Research Center, SDSU - All rights
reserved.
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Last
updated:
February 21, 2008 8:38 AM
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