ON ''SPURIOUS'' EDDIES Page: 2 of 11
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INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS
Int. J. Numer. Meth. Fluids 2000; 00:1-6 Prepared using fldauth.cls [Version: 2000/07/27 v1.0]
On "Spurious" Eddies
D. Drikakis', L.G. Margolin2, and P.K. Smolarkiewicz3
'Queen Mary, University of London, Engineering Department, London El 4NS, U.K.
2 Center for Nonlinear Science, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
3National Center for Atmospheric Research, Boulder, CO 80307, USA
Recently several papers have appeared in the CFD literature, proposing an idealized instability
problem as a benchmark for discriminating among numerical algorithms for two-dimensional Navier-
Stokes flows. The problem is a double shear layer simulated at coarse resolution and with a prescribed
interface perturbation. A variety of second-order accurate schemes have been tested, with all results
falling into one of two solution patterns - one pattern with two eddies and the other with three
eddies. In the literature, there is no fast-and-firm rule to predict the results of any particular
algorithm. However it is asserted that the two-eddy solution is correct. Our own research has led
to two conclusions. First, the appearance of the third eddy is tied up with small details of the
truncation error; we illustrate this point by prescribing small changes that lead to reversal of the
appearance/disappearance of the third eddy in several schemes. Second, we discuss the realizability of
the two solutions and suggest that the three-eddy solution is the more physical. Overall, we conclude
that this problem is a poor choice of benchmark to discriminate among numerical algorithms.
Copyright 2000 John Wiley & Sons, Ltd.
KEY WORDS: Unsteady flows; vortices; high-resolution methods
We investigate the formation of spurious vortical structures in time- dependent simulations of
incompressible flow. Our work is motivated by previous studies (, and the references therein)
that have documented the formation of "spurious eddies" in coarsely resolved simulations of
2D vortex-street flows. In general, we seek an understanding and control of the numerical
mechanisms that underlie the formation of these spurious structures. Our study demonstrates
the sensitivity of the simulated behavior of flows to the numerical discretization of the
advective terms, especially when vorticity dynamics plays an essential role in flow evolution.
This sensitivity is of particular relevance to large eddy simulation (LES) of turbulent flows.
In LES, the advective term discretization can alter the simulated large-eddy structures and
subsequently overwhelm the effects of unresolved scales estimated by a subgrid scale model.
An understanding of these issues will lead to better algorithms, including the consistent design
of spatio-temporal filters and subgrid scale models.
Copyright @ 2000 John Wiley & Sons, Ltd.
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Drikakis, D.; Margolin, L. & Smolarkiewicz, P. ON ''SPURIOUS'' EDDIES, article, February 1, 2001; New Mexico. (digital.library.unt.edu/ark:/67531/metadc720384/m1/2/: accessed August 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.