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Buoyancy-induced effects on large-scale motions in differentially heated vertical channel flows studied in direct numerical simulations

Wetzel, Tim and Wagner, Claus (2018) Buoyancy-induced effects on large-scale motions in differentially heated vertical channel flows studied in direct numerical simulations. International Journal of Heat and Fluid Flow, 75, pp. 14-26. Elsevier. DOI: 10.1016/j.jheatfluidflow.2018.09.005 ISSN 0142-727X

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Official URL: https://doi.org/10.1016/j.ijheatfluidflow.2018.09.005

Abstract

Direct numerical simulations of turbulent convection in a differentially heated vertical channel flow with Prandtl number Pr = 0.71 are conducted with a fourth-order accurate finite volume method for a bulk Reynolds number Re_b=4328 and three Grashof numbers Gr = {0, 6.4x10^5, 9.5x10^5}. The analysis of instantaneous flow field snapshots, first- and second-order moments, budget equations, power density spectra and quadrant analyses shows that the turbulent velocity fluctuations are attenuated in the aiding flow and enhanced in the opposing flow. In contrast, temperature fluctuations are attenuated in the opposing flow and enhanced in the aiding flow. The analyses further reveal that the low-momentum flow structures in the aiding flow are warmer than the high-momentum flow structures and vice versa in the opposing flow. Due to their different temperatures, buoyancy accelerates and decelerates the flow structures differently, which leads to reduced and increased pressure and shear fluctuations in the aiding and opposing flow. Thus, the redistribution of turbulent velocity fluctuations is lower in the aiding flow and higher in the opposing flow. The Reynolds shear stresses are consequently decreased in the former and increased in the latter, influencing the production of streamwise velocity fluctuations accordingly. In summary, the discussed physical mechanisms underline the indirect effect of buoyancy on the turbulent velocity fluctuations.

Item URL in elib:https://elib.dlr.de/120666/
Document Type:Article
Title:Buoyancy-induced effects on large-scale motions in differentially heated vertical channel flows studied in direct numerical simulations
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Wetzel, Timtim.wetzel (at) dlr.deUNSPECIFIED
Wagner, Clausclaus.wagner (at) dlr.deUNSPECIFIED
Date:17 November 2018
Journal or Publication Title:International Journal of Heat and Fluid Flow
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:75
DOI :10.1016/j.jheatfluidflow.2018.09.005
Page Range:pp. 14-26
Editors:
EditorsEmail
Jakirlic, SuadUNSPECIFIED
Publisher:Elsevier
Series Name:elvesier science direct
ISSN:0142-727X
Status:Published
Keywords:direct numerical simulation; turbulent mixed convection; turbulence attenuation; channel flow; buoyancy
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Transport
HGF - Program Themes:Terrestrial Vehicles (old)
DLR - Research area:Transport
DLR - Program:V BF - Bodengebundene Fahrzeuge
DLR - Research theme (Project):V - Next Generation Train III (old)
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Ground Vehicles
Deposited By: Wetzel, Tim
Deposited On:23 Nov 2018 17:29
Last Modified:06 Sep 2019 15:26

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