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Coherent structures in turbulent mixed convection flows through channels with differentially heated walls

Wagner, Claus and Wetzel, Tim (2022) Coherent structures in turbulent mixed convection flows through channels with differentially heated walls. GAMM Mitteilungen, pp. 1-18. Wiley. doi: 10.1002/gamm.202200006. ISSN 0936-7195.

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Official URL: https://doi.org/10.1002/gamm.202200006


The occurrence and shape of turbulent structures in mixed convection flows through a differently heated vertical channel are investigated in terms of thermally induced attenuation and amplification of turbulent velocity, pressure, and temperature fluctuations using direct numerical simulations. It is shown that the wall-normal momentum transport is decreased and increased near the heated and cooled wall, respectively, and that this leads to a reduced and elevated production of turbulent velocity fluctuations in the streamwise velocity component in the aiding and opposing flow, respectively. The corresponding flow structures are smoother, faster and warmer in the aiding flow and aligned along the main flow, while the colder structures in the opposing flow are more frayed and less directed. The warmer flow structures in the aiding flow are overall more stable than the colder structures in the opposing flow. Besides, the study reveals that the position of the maximum temperature fluctuations moves toward the heated wall, so that the sweeps produced at the two walls are affected differently by the former. As a consequence, the distance and time period over which the fluctuations develop in the aiding flow are shorter than in the opposing flow. It is further shown that vortex structures oriented in the streamwise direction usually arise with an offset to the right or left above a sweep or an ejection, whereby the decreasing values of the correlation coefficients with increasing Grashof number indicate a weakening of the vortex structures. Since none of the evaluated vortex criteria, that is, the distributions of the vorticity, lambda_2- value or Rortex-value correlate well with the evaluated minima of the pressure fluctuations, they do not allow a clear identification of the vortex structures. Finally, analyzing the budget of the turbulent kinetic energy it is confirmed that the velocity fluctuations are only indirectly influenced by the buoyancy force. Thus, the attenuation and amplification of the turbulent velocity fluctuations is reflected in the reduction and exaggeration of the Reynolds shear stresses in the aiding and opposing flow, respectively

Item URL in elib:https://elib.dlr.de/185922/
Document Type:Article
Title:Coherent structures in turbulent mixed convection flows through channels with differentially heated walls
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Wagner, ClausUNSPECIFIEDhttps://orcid.org/0000-0003-2273-0568UNSPECIFIED
Date:27 February 2022
Journal or Publication Title:GAMM Mitteilungen
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Page Range:pp. 1-18
EditorsEmailEditor's ORCID iDORCID Put Code
Keywords:DNS, coherent structures, differentially heated channel, mixed convection flow
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 (old)
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Ground Vehicles
Deposited By: Wagner, Prof. Dr.-Ing. Claus
Deposited On:07 Apr 2022 12:22
Last Modified:27 Jun 2023 13:30

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