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Experimental study of the global flow state transformation in a rectangular Rayleigh-Bénard sample

Horstmann, Gerrit Maik and Schiepel, Daniel and Wagner, Claus (2018) Experimental study of the global flow state transformation in a rectangular Rayleigh-Bénard sample. International Journal of Heat and Mass Transfer, 126, pp. 1333-1346. Elsevier. ISSN 0017-9310

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Official URL: https://www.journals.elsevier.com/international-journal-of-heat-and-mass-transfer/

Abstract

Large-scale flow structures were measured in a rectangular Rayleigh-Bénard sample of equal length and height of 10 cm and a depth of 2.5 cm. The working fluid was water at a Prandtl number of Pr = 6.9. Aiming to capture flow structures to their full extent and throughout the entire sample, the three-dimensional Lagrangian measurement technique 3D Particle Tracking Velocimetry (3DPTV) was employed. The study provides direct confirmation that the global mean flow field changes significantly in dependence of the Rayleigh number Ra within the investigated range of 2.1 x 10^6 < Ra < 4.5 x 10^8. Several distinguishable flow states were observed in the laminarturbulent transition regime complementing the well-known mean wind. A 2D mode decomposition reveals a break down of the mean wind during the transition phase and its new formation in the turbulent regime. Further, the global distribution of magnitudes of the instantaneous velocity fields was used to extract characteristic velocities in the flow field. It is showed, that the Reynoldsnumber-dependent scaling law Re ~ Ra^gamma can be unambiguously determined with directly measured Lagrangian velocities, since the same scaling behavior holds for all chosen reference velocities. In this context, using the product of a polynomial with an exponential function, the global velocity distribution is described analytically in dependence of Ra and four independent fit parameters in the sub-range 2.8 x 10^7 < Ra < 4.5 x 10^8.

Item URL in elib:https://elib.dlr.de/112406/
Document Type:Article
Additional Information:https://www.sciencedirect.com/science/article/pii/S0017931017307305
Title:Experimental study of the global flow state transformation in a rectangular Rayleigh-Bénard sample
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Horstmann, Gerrit Maikgerrit.horstmann (at) dlr.deUNSPECIFIED
Schiepel, Danieldaniel.schiepel (at) dlr.deUNSPECIFIED
Wagner, ClausClaus.Wagner (at) dlr.deUNSPECIFIED
Date:2018
Journal or Publication Title:International Journal of Heat and Mass Transfer
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:126
Page Range:pp. 1333-1346
Publisher:Elsevier
Series Name:Elsevier
ISSN:0017-9310
Status:Published
Keywords:Rayleigh-Bénard Convection, Large-scale Flow Structures, Mean Wind, 3D-PTV, 2DMode Decomposition
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 > Fluid Systems, GO
Deposited By: Bachmann, Barbara
Deposited On:27 Jun 2018 11:08
Last Modified:06 Sep 2019 15:16

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