On application of empirical mode decomposition for turbulence analysis in open-channel flows

Andrea Zampiron; Stuart M. Cameron; Vladimir I. Nikora

doi:10.1080/00221686.2023.2241838

On application of empirical mode decomposition for turbulence analysis in open-channel flows

Andrea Zampiron^* (Corresponding Author), Stuart M. Cameron, Vladimir I. Nikora

^*Corresponding author for this work

Engineering

Research output: Contribution to journal › Comment/debate › peer-review

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Abstract

Large-scale coherent structures are key elements of open-channel flow turbulence, quantification of which remains elusive. In this work, we use empirical mode decomposition (EMD) to break down a velocity time series into different modes, denoted as “intrinsic mode functions” (IMFs). Analysis of velocity auto- and co-spectra indicates that large-scale (LSMs) and very large-scale (VLSMs) fluid motions are sufficiently represented by particular groups of IMFs. A correlation between LSMs and VLSMs, identified by the EMD analysis, was found to generate 7% of the Reynolds shear stresses. However, the EMD analysis of surrogate velocity signals with randomized spectral phases demonstrated that the revealed correlation is actually an artefact of the EMD approach and should not be interpreted physically.

Original language	English
Pages (from-to)	788-795
Number of pages	8
Journal	Journal of Hydraulic Research
Volume	61
Issue number	5
Early online date	13 Sept 2023
DOIs	https://doi.org/10.1080/00221686.2023.2241838
Publication status	Published - 13 Sept 2023

Bibliographical note

The study has been supported by the EPSRC/UK grants: “Bed friction in rough-bed free-surface flows: a theoretical framework, roughness regimes, and quantification” (EP/K041088/1) and “Secondary currents in turbulent flows over rough walls” (EP/V002414/1).

Data Availability Statement

Supplemental data for this article can be accessed https://doi.org/10.1080/00221686.2023.2241838.

Keywords

Coherent structures
empirical mode decomposition
open-channel flow
turbulence
velocity spectra

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Cite this

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title = "On application of empirical mode decomposition for turbulence analysis in open-channel flows",

abstract = "Large-scale coherent structures are key elements of open-channel flow turbulence, quantification of which remains elusive. In this work, we use empirical mode decomposition (EMD) to break down a velocity time series into different modes, denoted as “intrinsic mode functions” (IMFs). Analysis of velocity auto- and co-spectra indicates that large-scale (LSMs) and very large-scale (VLSMs) fluid motions are sufficiently represented by particular groups of IMFs. A correlation between LSMs and VLSMs, identified by the EMD analysis, was found to generate 7% of the Reynolds shear stresses. However, the EMD analysis of surrogate velocity signals with randomized spectral phases demonstrated that the revealed correlation is actually an artefact of the EMD approach and should not be interpreted physically.",

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note = "The study has been supported by the EPSRC/UK grants: “Bed friction in rough-bed free-surface flows: a theoretical framework, roughness regimes, and quantification” (EP/K041088/1) and “Secondary currents in turbulent flows over rough walls” (EP/V002414/1).",

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AU - Cameron, Stuart M.

AU - Nikora, Vladimir I.

N1 - The study has been supported by the EPSRC/UK grants: “Bed friction in rough-bed free-surface flows: a theoretical framework, roughness regimes, and quantification” (EP/K041088/1) and “Secondary currents in turbulent flows over rough walls” (EP/V002414/1).

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N2 - Large-scale coherent structures are key elements of open-channel flow turbulence, quantification of which remains elusive. In this work, we use empirical mode decomposition (EMD) to break down a velocity time series into different modes, denoted as “intrinsic mode functions” (IMFs). Analysis of velocity auto- and co-spectra indicates that large-scale (LSMs) and very large-scale (VLSMs) fluid motions are sufficiently represented by particular groups of IMFs. A correlation between LSMs and VLSMs, identified by the EMD analysis, was found to generate 7% of the Reynolds shear stresses. However, the EMD analysis of surrogate velocity signals with randomized spectral phases demonstrated that the revealed correlation is actually an artefact of the EMD approach and should not be interpreted physically.

AB - Large-scale coherent structures are key elements of open-channel flow turbulence, quantification of which remains elusive. In this work, we use empirical mode decomposition (EMD) to break down a velocity time series into different modes, denoted as “intrinsic mode functions” (IMFs). Analysis of velocity auto- and co-spectra indicates that large-scale (LSMs) and very large-scale (VLSMs) fluid motions are sufficiently represented by particular groups of IMFs. A correlation between LSMs and VLSMs, identified by the EMD analysis, was found to generate 7% of the Reynolds shear stresses. However, the EMD analysis of surrogate velocity signals with randomized spectral phases demonstrated that the revealed correlation is actually an artefact of the EMD approach and should not be interpreted physically.

KW - Coherent structures

KW - empirical mode decomposition

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KW - turbulence

KW - velocity spectra

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On application of empirical mode decomposition for turbulence analysis in open-channel flows

Abstract

Bibliographical note

Data Availability Statement

Keywords

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