Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study

Bernhard  Vowinckel; Vladimir Nikora; Tobias  Kempe; Jochen  Fröhlich

doi:10.1080/00221686.2016.1260658

Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study

Bernhard Vowinckel^* (Corresponding Author), Vladimir Nikora, Tobias Kempe, Jochen Fröhlich

^*Corresponding author for this work

Engineering

Technische Universität Dresden

Research output: Contribution to journal › Article › peer-review

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Abstract

Based on direct numerical simulations, the paper investigates momentum fluxes and hydrodynamic stresses within and above a mobile granular bed in a turbulent open-channel flow laden with monodisperse spherical particles. Two simulation scenarios are considered: one with partially mobilized particles (“heavy” particles) and another with all particles in motion (“light” particles). The momentum fluxes were computed as temporal and spatial averages following the double-averaging methodology for rough-bed flows. The analysis, hence, allows the DNS data to be convoluted in a rigorous way to provide detailed description and quantification of the physical mechanisms involved in momentum exchanges. In particular, it was found that heavy particles create streamwise bedforms causing heterogeneity in the spanwise direction. This yields significant form-induced momentum fluxes that cannot be neglected. For both scenarios, the mobile particles take up a substantial amount of the momentum supplied, which ultimately increases the hydraulic resistance of the channel. These effects enhance and stabilize secondary flows in the channel.

Original language	English
Pages (from-to)	208-223
Number of pages	16
Journal	Journal of Hydraulic Research
Volume	55
Issue number	2
Early online date	16 Jan 2017
DOIs	https://doi.org/10.1080/00221686.2016.1260658
Publication status	Published - 1 Mar 2017

Bibliographical note

Acknowledgements
The authors gratefully acknowledge the Centre for Information Services and High Performance Computing (ZIH), Dresden, and the Jülich Supercomputing Centre (JSC) for providing computing time. The authors thank Markus Uhlmann and Clemens Chan-Braun for stimulating discussions on bed-load transport.

Funding
The present work was funded by the German Research Foundation (DFG) via the project [FR 1593/5-2] and was partly supported by the Engineering and Physical Sciences Research Council (EPSRC) UK, Grant [EP/G056404/1].

Keywords

bedforms
direct numerical simulations
double-averaging methodology
particle-laden flows
secondary currents
turbulence-sediments interactions

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10.1080/00221686.2016.1260658Licence: CC BY

Spatially averaged momentum fluxes and stresses in flows over mobile granular beds a DNS based study
© 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Final published version, 3.67 MBLicence: CC BY

V.I. Nikora
- Engineering, Engineering - Sixth Century Chair in Environmental Fluid Mechanics
Person: Academic

Cite this

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title = "Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study",

abstract = "Based on direct numerical simulations, the paper investigates momentum fluxes and hydrodynamic stresses within and above a mobile granular bed in a turbulent open-channel flow laden with monodisperse spherical particles. Two simulation scenarios are considered: one with partially mobilized particles (“heavy” particles) and another with all particles in motion (“light” particles). The momentum fluxes were computed as temporal and spatial averages following the double-averaging methodology for rough-bed flows. The analysis, hence, allows the DNS data to be convoluted in a rigorous way to provide detailed description and quantification of the physical mechanisms involved in momentum exchanges. In particular, it was found that heavy particles create streamwise bedforms causing heterogeneity in the spanwise direction. This yields significant form-induced momentum fluxes that cannot be neglected. For both scenarios, the mobile particles take up a substantial amount of the momentum supplied, which ultimately increases the hydraulic resistance of the channel. These effects enhance and stabilize secondary flows in the channel.",

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note = "Acknowledgements The authors gratefully acknowledge the Centre for Information Services and High Performance Computing (ZIH), Dresden, and the J{\"u}lich Supercomputing Centre (JSC) for providing computing time. The authors thank Markus Uhlmann and Clemens Chan-Braun for stimulating discussions on bed-load transport. Funding The present work was funded by the German Research Foundation (DFG) via the project [FR 1593/5-2] and was partly supported by the Engineering and Physical Sciences Research Council (EPSRC) UK, Grant [EP/G056404/1].",

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AU - Fröhlich, Jochen

N1 - Acknowledgements The authors gratefully acknowledge the Centre for Information Services and High Performance Computing (ZIH), Dresden, and the Jülich Supercomputing Centre (JSC) for providing computing time. The authors thank Markus Uhlmann and Clemens Chan-Braun for stimulating discussions on bed-load transport. Funding The present work was funded by the German Research Foundation (DFG) via the project [FR 1593/5-2] and was partly supported by the Engineering and Physical Sciences Research Council (EPSRC) UK, Grant [EP/G056404/1].

PY - 2017/3/1

Y1 - 2017/3/1

N2 - Based on direct numerical simulations, the paper investigates momentum fluxes and hydrodynamic stresses within and above a mobile granular bed in a turbulent open-channel flow laden with monodisperse spherical particles. Two simulation scenarios are considered: one with partially mobilized particles (“heavy” particles) and another with all particles in motion (“light” particles). The momentum fluxes were computed as temporal and spatial averages following the double-averaging methodology for rough-bed flows. The analysis, hence, allows the DNS data to be convoluted in a rigorous way to provide detailed description and quantification of the physical mechanisms involved in momentum exchanges. In particular, it was found that heavy particles create streamwise bedforms causing heterogeneity in the spanwise direction. This yields significant form-induced momentum fluxes that cannot be neglected. For both scenarios, the mobile particles take up a substantial amount of the momentum supplied, which ultimately increases the hydraulic resistance of the channel. These effects enhance and stabilize secondary flows in the channel.

AB - Based on direct numerical simulations, the paper investigates momentum fluxes and hydrodynamic stresses within and above a mobile granular bed in a turbulent open-channel flow laden with monodisperse spherical particles. Two simulation scenarios are considered: one with partially mobilized particles (“heavy” particles) and another with all particles in motion (“light” particles). The momentum fluxes were computed as temporal and spatial averages following the double-averaging methodology for rough-bed flows. The analysis, hence, allows the DNS data to be convoluted in a rigorous way to provide detailed description and quantification of the physical mechanisms involved in momentum exchanges. In particular, it was found that heavy particles create streamwise bedforms causing heterogeneity in the spanwise direction. This yields significant form-induced momentum fluxes that cannot be neglected. For both scenarios, the mobile particles take up a substantial amount of the momentum supplied, which ultimately increases the hydraulic resistance of the channel. These effects enhance and stabilize secondary flows in the channel.

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DO - 10.1080/00221686.2016.1260658

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Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study

Abstract

Bibliographical note

Keywords

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V.I. Nikora

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