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   -> Volume 6, Issue 10


Preprint: Cross-correlation based on complex-wavelet transforms
 
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Guido Buresti (buresti@docenti.ing.unipi.it)
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PostPosted: Wed Sep 24, 1997 5:34 pm    
Subject: Preprint: Cross-correlation based on complex-wavelet transforms
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#7 Preprint: Cross-correlation based on complex-wavelet transforms

Dear Sirs,

I would like to inform you of two recent papers regarding a new
cross-correlation technique based on the complex-wavelet continuous
transform. The technique allows the time-local contribution of each
scale to the correlation of two signals to be characterized; the
time-local phase difference between the the fluctuations of the two
signals at each frequency may also be obtained. In the present papers
the technique is applied to the analysis of fluctuating velocity
signals derived in the first from the direct numerical solution of the
flow equations, and in the second from wind tunnel experiments.

For further information, please contact:
Prof. Guido Buresti
Dip. Ing. Aerospaziale - Universita' di Pisa
Via Diotisalvi, 2 - 56126 PISA - Italy
tel: +39-50-550200 fax: +39-50-553654
E-mail: buresti@ing.unipi.it =

Title:

Application of a wavelet cross-correlation analysis to DNS velocity
signals.
European Journal of Mechanics B/ Fluids, Vol. 16, N. 4, 1997, pp.
575-597

Authors:

M. Onorato Jr., M.V. Salvetti, G. Buresti, P. Petagna =

Abstract: A wavelet cross-correlation analysis is applied to the
velocity signals derived from axisymmetric direct numerical
simulations of a coaxial jet configuration. It is shown that this
technique permits to determine the time intervals and scales
contributing to the Reynolds stresses, and thus to assess the level of
intermittency of this contribution at the various scales. The
availability of the vorticity field from the numerical simulations
permits also to associate roll-up, passage and pairing of vortical
structures with average, spectral and instantaneous contributions to
the Reynolds stresses. High values of Reynolds stresses are found in
the roll-up region, where the axial and radial velocity fluctuations
have a small phase lag for significant time intervals. Conversely,
more downstream the passage of approximately symmetrical vortices,
although giving rise to high velocity fluctuations, does not produce
significant Reynolds stresses because the two velocity signals are
nearly orthogonal for most of the time. This demonstrates that
eduction schemes based on the energy of the velocity fluctuations
might not adequately reproduce the flow features characterizing the
Reynolds stress production.

Title:
Low aspect-ratio triangular prisms in cross-flow: measurements of the
wake fluctuating velocity field
Proc. 2nd European and African Conference on Wind Engineering, SGE Ed.,
1997, pp. 743-750.

Authors:
G. Buresti, G. Lombardi, A. Talamelli

Abstract: An experimental investigation is carried out to study the
characteristics of the fluctuating wake flow field of finite-length
prismatic bodies in cross-flow, placed vertically on a plane and
having isosceles triangular cross-section with 60=B0 or 90=B0 apex
angle orienta= ted in the downstream direction. The wake fluctuating
field is studied with hot-wire anemometry for aspect ratios h/w =3D
1.0, 1.5, 2.0 and 3.0 at Re==3D wU/n @ 1.2 x 105, and the velocity
signals are analysed by means of procedures based on the wavelet
transform. Velocity fluctuations with a clear dominating frequency are
found immediately outside the wake along all the models, even if their
magnitude decreases at a height corresponding to the free end of the
bodies. The wavelet analysis of the phase difference between signals
acquired at opposite sides of the wake shows that alternate vortex
shedding occurs for all the models. An increase in the phase shift
between the fluctuations on the same side of the wake with increasing
vertical distance between the probes suggests that the shed vortices
are curved. No evidence of symmetrical shedding or of the presence of
arch-type vortices is found, even for the models with the smaller
aspect ratios.
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