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Reversals of coherent structures in turbulent mixed convection

Mommert, Michael and Schiepel, Daniel and Schmeling, Daniel and Wagner, Claus (2020) Reversals of coherent structures in turbulent mixed convection. Journal of Fluid Mechanics, 904, A33-1-A33-33. Cambidge University Press. doi: 10.1017/jfm.2020.705. ISSN 0022-1120.

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Official URL: https://doi.org/10.1017/jfm.2020.705

Abstract

Reconfiguration events in turbulent mixed convection, i.e. the superposition of thermal and forced flow contributions, at the two different Richardson numbers Ri=1.5 and Ri=3.7 and similar Rayleigh numbers of Ra≈10^8 are investigated with tomographic particle image velocimetry in combination with local temperature measurements. For both cases, the three-dimensional velocity fields reflect diagonally aligned large-scale circulations (LSC) switching their alignment by rotating their axes around a pivot located at the centre of the LSC, while the temperatures perform a translation movement of the structures in agreement with earlier temperature-based investigations. For the high Ri case, the switching process of the observed spontaneous reconfigurations is induced by a reversing thermal flow contribution while the forced flow contribution is constant. Furthermore, it is shown that a secondary roll structure, which drives the reconfiguration process in Rayleigh–Bénard convection, also exists in mixed convection. However, in the latter, the flow reversals are triggered by different structures which accumulate and release their kinetic energy according to a proper orthogonal decomposition analysis. In contrast, for the low Ri case, the structure formation during continuous reconfigurations is governed by a Taylor- or Görtler-type instability. This means that the forced convection substantially affects the reconfiguration mechanism of these structures. Therefore, the reconfigurations cannot be described by a simple superposition of structures associated with the two flow contributions as for the high Ri.

Item URL in elib:https://elib.dlr.de/134154/
Document Type:Article
Title:Reversals of coherent structures in turbulent mixed convection
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Mommert, MichaelMichael.Mommert (at) dlr.dehttps://orcid.org/0000-0002-7817-3388
Schiepel, Danieldaniel.schiepel (at) dlr.dehttps://orcid.org/0000-0002-3703-3514
Schmeling, DanielDaniel.Schmeling (at) dlr.dehttps://orcid.org/0000-0003-2712-9974
Wagner, ClausClaus.Wagner (at) dlr.deUNSPECIFIED
Date:13 October 2020
Journal or Publication Title:Journal of Fluid Mechanics
Open Access:Yes
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:904
DOI :10.1017/jfm.2020.705
Page Range:A33-1-A33-33
Editors:
EditorsEmailEditor's ORCID iD
UNSPECIFIEDCambridge University PressUNSPECIFIED
Publisher:Cambidge University Press
ISSN:0022-1120
Status:Published
Keywords:buoyancy-driven instability, convection in cavities, turbulent convection
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 - NGT BIT
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Ground Vehicles
Deposited By: Mommert, Michael
Deposited On:19 Oct 2020 12:02
Last Modified:19 Oct 2020 12:02

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