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Large-scale volumetric flow measurement in a pure thermal plume by dense tracking of helium-filled soap bubbles

Huhn, Florian and Schanz, Daniel and Gesemann, Sebastian and Dierksheide, Uwe and van de Meerendonk, Remco and Schröder, Andreas (2017) Large-scale volumetric flow measurement in a pure thermal plume by dense tracking of helium-filled soap bubbles. Experiments in Fluids, 58 (116). Springer. DOI: 10.1007/s00348-017-2390-2 ISSN 0723-4864

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Official URL: https://doi.org/10.1007/s00348-017-2390-2

Abstract

We present a spatially and temporally highly resolved flow measurement covering a !arge volume (~o.6 m3) in a pure thermal plume in air. The thermal plume develops above an extended heat source and is characterized by moderate velocities (U~0.35 m/s) with a Reynolds number of Re~500 and a Rayleigh number of Ra~100000. We demonstrate the requirements and capa bilities of the measurement equipment and the particle tracking approach to be able to probe measurement volumes up to and beyond one cubic meter. The use of !arge tracer particles (300 µm), helium-filled soap bubbles (HFSBs), is crucial and yields high particle image quality over large-volume depths when illuminated with arrays of pulsed high-power LEDs. The experimental limitations of the HFSBs-their limited lifetime and their intensity loss over time-are quantified. The HFSBs' uniform particle images allows an accurate reconstruction of the flow using Shake-The-Box particle tracking with high partlcle concentrations up to 0.1 particles per pixel. This enables tracking of up to 275,000 HFSBs simultaneously. After interpolating the scattered data onto a regular grid with a Navier-Stokes regularization, the velocity field of the thermal plume reveals a multitude of vortices with a smooth temporal evolution and a remarkable coherence in time (see animation, supplementary data). Acceleration fields are also derived from interpolated particle tracks and complement the flow measurement. Additionally, the flow map, the basis of a !arge dass of Lagrangian coherent structures, is computed directly from observed particle tracks. We show entrainment regions and coherent vortices of the thermal plume in the flow map and compute fields of the finite-time Lyapunov exponent.

Item URL in elib:https://elib.dlr.de/116880/
Document Type:Article
Additional Information:ISSN 1432-1114 (Online); Published online: 03. August 2017; Vol.: 58, lssue 9, Sept. 2017, Article 116, Publisher: Springer Berlin Heidelberg
Title:Large-scale volumetric flow measurement in a pure thermal plume by dense tracking of helium-filled soap bubbles
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Huhn, Florianflorian.huhn (at) dlr.deUNSPECIFIED
Schanz, Danieldaniel.schanz (at) dlr.deUNSPECIFIED
Gesemann, Sebastiansebastian.gesemann (at) dlr.deUNSPECIFIED
Dierksheide, UweLaVision, GöttingenUNSPECIFIED
van de Meerendonk, RemcoAerospace Engineering Department, Delft University of Technology, 2629, The NetherlandsUNSPECIFIED
Schröder, AndreasAndreas.Schroeder (at) dlr.deUNSPECIFIED
Date:March 2017
Journal or Publication Title:Experiments in Fluids
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:58
DOI :10.1007/s00348-017-2390-2
Editors:
EditorsEmail
UNSPECIFIEDSpringer Berlin Heidelberg
Publisher:Springer
ISSN:0723-4864
Status:Published
Keywords:Shake-The-Box, thermal plume, helium-filled soap bubbles, Lagrangian particle tracking
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:fixed-wing aircraft
DLR - Research area:Aeronautics
DLR - Program:L AR - Aircraft Research
DLR - Research theme (Project):L - Simulation and Validation
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Experimental Methods, GO
Deposited By: Bachmann, Barbara
Deposited On:13 Dec 2017 14:34
Last Modified:06 Sep 2019 15:25

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