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How far does the influence of the free surface extend in turbulent open channel flow?

Bauer, Christian und Sakai, Yoshiyuki und Uhlmann, Markus (2025) How far does the influence of the free surface extend in turbulent open channel flow? Flow Turbulence and Combustion, 115, Seiten 447-468. Springer. doi: 10.1007/s10494-025-00665-4. ISSN 1386-6184.

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Offizielle URL: https://link.springer.com/content/pdf/10.1007/s10494-025-00665-4.pdf

Kurzfassung

Turbulent open channel flow is known to feature a multi-layer structure near the free surface. In the present work we employ direct numerical simulations considering Reynolds numbers up to \mathrm{Re}_\tau=900$ and domain sizes large enough ($L_x=12 \pi h$, $L_z=4 \pi h$) to faithfully capture the effect of very-large-scale motions in order to test the proposed scaling laws an ultimately answer the question: How far does the influence of the free surface extend? In the region near the free surface, where fluctuation intensities of velocity and vorticity become highly anisotropic, we observe the previously documented triple-layer structure, consisting of a wall-normal velocity damping layer that scales with the channel height $h$, and two sublayers that scale with the near-surface viscous length scale $\ell_\mathrm{V}=\mathrm{Re}_\mathrm{b}^{-1/2}h$ and with the Kolmogorov length scale $\ell_\mathrm{K}=\mathrm{Re}_\mathrm{b}^{-3/4}h$, respectively. The scaling laws previously proposed by Calmet and Magnaudet [J. Fluid. Mech. \textbf{474}, 355--378 (2003)] are found to hold with the following exceptions. The thin layer, where the intensity of surface-parallel components of the vorticity rapidly decreases to zero, is here found to scale with the Kolmogorov length scale $\ell_\mathrm{K}$ rather than with the near-surface viscous scale $\ell_\mathrm{V}$. In addition, we argue that the Kolmogorov length scale is the relevant scale for the mean velocity gradient near the free surface. Both the mean velocity gradient and the fluctuation intensity of the surface-parallel component of vorticity decay to zero in the Kolmogorov sublayer $\delta_\mathrm{K} \approx 20 \ell_\mathrm{K}$. On the other hand, the layer, where the wall-normal turbulence intensity decreases linearly to zero near the free surface, scales with $\ell_\mathrm{V}$ rather than $\ell_\mathrm{K}$ as suggested by Calmet and Magnaudet. The corresponding near-surface viscous sublayer measures $\delta_\mathrm{V} \approx \ell_\mathrm{V}$. Importantly, the streamwise turbulence intensity profile for $\mathrm{Re}_\tau \ge 400$ suggests that the influence of the free-slip boundary penetrates essentially all the way down to the solid wall through the appearance of enhanced very-large-scale motions ($ delta_{\mathrm{SIL}}\approx h$). In contrast, the layer where the surface-normal turbulence intensity is damped to zero is restricted to the free surface ($\delta_{\mathrm{NVD}}\approx 0.3h$). As a consequence, the partitioning of the surface-influenced region has to be expanded to a four-layer structure that spans the entire channel height $h$.

elib-URL des Eintrags:https://elib.dlr.de/214076/
Dokumentart:Zeitschriftenbeitrag
Titel:How far does the influence of the free surface extend in turbulent open channel flow?
Autoren:
AutorenInstitution oder E-Mail-AdresseAutoren-ORCID-iDORCID Put Code
Bauer, ChristianChristian.Bauer (at) dlr.dehttps://orcid.org/0000-0003-1838-6194NICHT SPEZIFIZIERT
Sakai, YoshiyukiTU MünchenNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Uhlmann, MarkusKITNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Datum:16 Juni 2025
Erschienen in:Flow Turbulence and Combustion
Referierte Publikation:Ja
Open Access:Ja
Gold Open Access:Nein
In SCOPUS:Ja
In ISI Web of Science:Ja
Band:115
DOI:10.1007/s10494-025-00665-4
Seitenbereich:Seiten 447-468
Herausgeber:
HerausgeberInstitution und/oder E-Mail-Adresse der HerausgeberHerausgeber-ORCID-iDORCID Put Code
Salvetti, Maria VittoriaERCOFTACNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Kempf, Andreas M.ERCOFTACNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Verlag:Springer
Name der Reihe:Springer Nature Link
ISSN:1386-6184
Status:veröffentlicht
Stichwörter:turbulent open channel flow, direct numerical simulation, free surface
HGF - Forschungsbereich:Luftfahrt, Raumfahrt und Verkehr
HGF - Programm:Verkehr
HGF - Programmthema:Schienenverkehr
DLR - Schwerpunkt:Verkehr
DLR - Forschungsgebiet:V SC Schienenverkehr
DLR - Teilgebiet (Projekt, Vorhaben):V - RoSto - Rolling Stock
Standort: Göttingen
Institute & Einrichtungen:Institut für Aerodynamik und Strömungstechnik > Bodengebundene Fahrzeuge
Hinterlegt von: Bauer, Christian
Hinterlegt am:18 Jun 2025 15:49
Letzte Änderung:09 Sep 2025 20:41

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