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Quantification of amplitude modulation in wall-bounded turbulence
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-1663-3553
Karlsruhe Inst Technol, Inst Fluid Mech, Kaiserstr 10, D-76131 Karlsruhe, Germany..
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-6570-5499
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2019 (English)In: Fluid Dynamics Research, ISSN 0169-5983, E-ISSN 1873-7005, Vol. 51, no 1, article id 011408Article in journal (Refereed) Published
Abstract [en]

Many recent investigations on the scale interactions in wall-bounded turbulent flows focus on describing so-called amplitude modulation, the phenomenon that deals with the influence of large scales in the outer region on the amplitude of the small-scale fluctuations in the near-wall region. The present study revisits this phenomenon regarding two aspects, namely the method for decomposing the scales and the quantification of the modulation. First, the paper presents a summary of the literature that has dealt with either or both aspects. Second, for decomposing the scales, different spectral filters (temporal, spatial or both) and empirical mode decomposition (EMD) are evaluated and compared. The common data set is a well-resolved large-eddy simulation that offers a wide range of Reynolds numbers spanning Re-theta = 880-8200. The quantification of the amplitude modulation is discussed for the resulting scale components. Particular focus is given to evaluate the efficacy of the various filters to separate scales for the range of Reynolds numbers of interest. Different to previous studies, the different methods have been evaluated using the same data set, thereby allowing a fair comparison between the various approaches. It is observed that using a spectral filter in the spanwise direction is an effective approach to separate the small and large scales in the flow, even at comparably low Reynolds numbers, whereas filtering in time should be approached with caution in the low-to-moderate Re range. Additionally, using filters in both spanwise and time directions, which would separate both wide and long-living structures from the small and fast scales, gives a cleaner image for the small-scales although the contribution to the scales interaction from that filter implementation has been found negligible. Applying EMD to decompose the scales gives similar results to Fourier filters for the energy content of the scales and thereby for the quantification of the amplitude modulation using the decomposed scales. No direct advantage of EMD over classical Fourier filters could be seen. Potential issues regarding different decomposition methods and different definitions of the amplitude modulation are also discussed.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2019. Vol. 51, no 1, article id 011408
Keywords [en]
amplitude modulation, turbulent boundary layer, scale interaction
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-243936DOI: 10.1088/1873-7005/aaca81ISI: 000456203700009Scopus ID: 2-s2.0-85061429605OAI: oai:DiVA.org:kth-243936DiVA, id: diva2:1293980
Conference
Inernational Camp-Style Seminar on Dynamics of Wall-Bounded Shear Flows, AUG 31-SEP 02, 2016, Kyoto, JAPAN
Note

QC 20190306

Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2019-03-18Bibliographically approved

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Dogan, EdaÖrlü, RamisVinuesa, RicardoSchlatter, Philipp

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