Wavelet analysis of wall turbulence to study large-scale modulation of small scales

Baars, W, Talluru, K, Hutchins, N and Marusic, I 2015, 'Wavelet analysis of wall turbulence to study large-scale modulation of small scales', Experiments in Fluids, vol. 56, no. 10, pp. 1-15.

Document type: Journal Article
Collection: Journal Articles

Title Wavelet analysis of wall turbulence to study large-scale modulation of small scales
Author(s) Baars, W
Talluru, K
Hutchins, N
Marusic, I
Year 2015
Journal name Experiments in Fluids
Volume number 56
Issue number 10
Start page 1
End page 15
Total pages 15
Publisher Springer
Abstract Wavelet analysis is employed to examine amplitude and frequency modulations in broadband signals. Of particular interest are the streamwise velocity fluctuations encountered in wall-bounded turbulent flows. Recent studies have shown that an important feature of the near-wall dynamics is the modulation of small scales by large-scale motions. Small- and large-scale components of the velocity time series are constructed by employing a spectral separation scale. Wavelet analysis of the small-scale component decomposes the energy in joint time-frequency space. The concept is to construct a low-dimensional representation of the small-scale time-varying spectrum via two new time series: the instantaneous amplitude of the small-scale energy and the instantaneous frequency. Having the latter in a time-continuous representation allows a more thorough analysis of frequency modulation. By correlating the large-scale velocity with the concurrent small-scale amplitude and frequency realizations, both amplitude and frequency modulations are studied. In addition, conditional averages of the small-scale amplitude and frequency realizations depict unique features of the scale interaction. For both modulation phenomena, the much studied time shifts, associated with peak correlations between the large-scale velocity and small-scale amplitude and frequency traces, are addressed. We confirm that the small-scale amplitude signal leads the large-scale fluctuation close to the wall. It is revealed that the time shift in frequency modulation is smaller than that in amplitude modulation. The current findings are described in the context of a conceptual mechanism of the near-wall modulation phenomena.
Subject Aerodynamics (excl. Hypersonic Aerodynamics)
DOI - identifier 10.1007/s00348-015-2058-8
Copyright notice © 2015, Springer-Verlag Berlin Heidelberg.
ISSN 0723-4864
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