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Statistical and temporal characterization of turbulent Rayleigh Bénard convection boundary layers using time-resolved PIV measurements

Willert, Christian and du Puits, Ronald and Resagk, Christian (2014) Statistical and temporal characterization of turbulent Rayleigh Bénard convection boundary layers using time-resolved PIV measurements. WALLTURB - Progress in Wall Turbulence: Understanding and Modelling, 18.-20. Jun. 2014, Lille, France.

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This contribution reports on near-wall flow field measurements in turbulent Rayleigh-Bénard convection (RBC) in air at a fixed Prandtl number Pr=0.7 and Rayleigh number Ra = 1.45E10. For the experiment the large scale convection (LSC) was confined to a rectangular box of 2.5x2.5x0.65 m^3 made of transparent acrylic sheets. Prior video-graphic visualizations of the bottom boundary layer flow by means of laser light sheet illumination of small particles indicated the presence of highly dynamic flow behaviour at flow conditions that classical stability analysis predict to still be in the laminar regime. While theory predicts a transition to turbulence at Reynolds numbers R_\delta \appox 420 the present investigation exhibits highly unsteady flow at a much lower Reynolds number of Re_\delta \appox 260 based on boundary layer thickness. With the help of the PIV data it can be demonstrated that the entrainment of turbulent structures from the mean wind into the boundary layer acts, alongside with the destabilization due to inner shear, as a second mechanism on its path to turbulence. Both contributions must be considered when predicting the critical bound towards the ultimate regime of thermal convection. The measurements rely on the acquisition of long, continuous sequences of particle image velocimetry (PIV) data from which both statistical and spectral information can be retrieved. Contrary to conventional implementation of the PIV technique the field of view is restricted to a narrow strip, generally extending in wall-normal direction. In this way both the acquisition frequency and the total number images of the employed high speed camera are proportionally increased. The temporally oversampled data allows the use of multi-frame PIV processing algorithms which reduces measurement uncertainties with respect to standard dual-frame analysis.

Item URL in elib:https://elib.dlr.de/94592/
Document Type:Conference or Workshop Item (Speech)
Title:Statistical and temporal characterization of turbulent Rayleigh Bénard convection boundary layers using time-resolved PIV measurements
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Willert, Christianchris.willert (at) dlr.deUNSPECIFIED
du Puits, RonaldTechnische Universität IlmenauUNSPECIFIED
Resagk, ChristianTechnische Universität IlmenauUNSPECIFIED
Date:18 June 2014
Refereed publication:No
Open Access:No
Gold Open Access:No
In ISI Web of Science:No
Keywords:boundary layer, convection driven flow, Rayleigh Benard convection, transition to turbulence, wall-bounded flows, flow visualization, particle image velocimetry, turbulence statistics
Event Title:WALLTURB - Progress in Wall Turbulence: Understanding and Modelling
Event Location:Lille, France
Event Type:international Conference
Event Dates:18.-20. Jun. 2014
Organizer:École Centrale de Lille
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:propulsion systems
DLR - Research area:Aeronautics
DLR - Program:L ER - Engine Research
DLR - Research theme (Project):L - Virtual Engine and Validation methods (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Propulsion Technology > Engine Measurement Systems
Deposited By: Willert, Dr.phil. Christian
Deposited On:15 Jan 2015 15:47
Last Modified:16 Jan 2015 14:45

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