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Direct numerical simulation of turbulent open channel flow: Streamwise turbulence intensity scaling and its relation to large-scale coherent motions

Bauer, Christian and Sakai, Yoshiyuki and Uhlmann, Markus (2023) Direct numerical simulation of turbulent open channel flow: Streamwise turbulence intensity scaling and its relation to large-scale coherent motions. In: iTi X conference on turbulence 2023. iTi X Conference on Turbulence 2023, 2023-07-24 - 2023-07-26, Bertinoro, Italien.

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Official URL: https://www.fdy.tu-darmstadt.de/iti/itihome_2.en.jsp

Abstract

The well-known failure of wall-scaling of the streamwise turbulent intensity in closed channel flows (CCF) is associated with the appearance of very-large-scale motions (VLSMs, [1]). In turbulent open channel flow (OCF), VLSM are larger, more energetic and appear at lower Reynolds number than in CCF [2, 3]. Thus, to investigate the scaling of turbulence intensities and its relation to underlying coherent structures in OCF, we carried out direct numerical simulations of both OCF and CCF of friction Reynolds numbers up to Ret = 900 in large computational domains (Lx/h × Lz/h = 12pi × 4pi). Figure 1 shows the turbulent intensities normalized by the bulk flow velocity ub. Unlike CCF, where the streamwise turbulent intensity scales neither in wall nor in bulk units (figure 1b), our data suggests that urms in OCF scales with the bulk velocity ub for Ret > 400. This difference in scaling behavior of OCF with respect to CCF is presumably caused by contributions from VLSMs as depicted in figure 2(a,b). In OCF, VLSMs are linked to so-called super-streamwise vortices (SSVs), which are statistically difficult to track [6]. However, in figure 2(c,d) we visualize SSVs in terms of the two-point correlation of the streamfunction of the streamwise averaged crosssectional velocity components. Similar to VLSMs, SSVs are more intense in OCF than in CCF and they occur much more regularly in the shape of alternating positive and negative vortices. Summarizing, at the conference we are going to present new evidence of bulk scaling of the streamwise turbulence intensity in OCF and relate it to underlying coherent motions, such as VLSMs and SSVs. In addition, we are going to look at the scaling of the near-surface layers in OCF.

Item URL in elib:https://elib.dlr.de/196543/
Document Type:Conference or Workshop Item (Poster)
Title:Direct numerical simulation of turbulent open channel flow: Streamwise turbulence intensity scaling and its relation to large-scale coherent motions
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Bauer, ChristianUNSPECIFIEDhttps://orcid.org/0000-0003-1838-6194UNSPECIFIED
Sakai, YoshiyukiTUMUNSPECIFIEDUNSPECIFIED
Uhlmann, MarkusKITUNSPECIFIEDUNSPECIFIED
Date:24 July 2023
Journal or Publication Title:iTi X conference on turbulence 2023
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:direct numerical simulation, turbulent open channel flow
Event Title:iTi X Conference on Turbulence 2023
Event Location:Bertinoro, Italien
Event Type:international Conference
Event Start Date:24 July 2023
Event End Date:26 July 2023
Organizer:TU Darmstadt
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Transport
HGF - Program Themes:Rail Transport
DLR - Research area:Transport
DLR - Program:V SC Schienenverkehr
DLR - Research theme (Project):V - RoSto - Rolling Stock
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Ground Vehicles
Deposited By: Bauer, Christian
Deposited On:25 Aug 2023 15:57
Last Modified:24 Apr 2024 20:56

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