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Skin friction and coherent structures within a laminar separation bubble

Miozzi, Massimo and Capone, Alessandro and Costantini, Marco and Fratto, Lorenzo and Klein, Christian and Di Felice, Fabio (2019) Skin friction and coherent structures within a laminar separation bubble. Experiments in Fluids, 60 (1), pp. 1-25. Springer. DOI: 10.1007/s00348-018-2651-8 ISSN 0723-4864

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Official URL: https://link.springer.com/article/10.1007%2Fs00348-018-2651-8

Abstract

We study the Laminar Separation Bubble (LSB) which develops on the suction side of a NACA 0015 hydrofoil by means of a Temperature-Sensitive Paint (TSP), at a Reynolds number of 1.8x10⁵ and angles of attack AoA = [3°, 5°, 7°, 10°]. The thermal footprints T_w(x,y,t) of the fluid unveil three different flow regimes whose complexity in time and space decreases when AoA increases, up to 10° where the LSB-induced spatial gradients are linked to almost fixed positions in time. At AoA = 7° the LSB system undergoes through a 3D destabilization, that induces C-shaped arcs at separation and weak bubble-flapping at reattachment. Structural changes occur at AoA = 5° and 3°: bubble-flapping raises homogeneously at reattachment while intermittent, wedge- shaped events alter the LSB shape. The relative skin-friction vector fields τ_w(x,y,t), extracted from T_w(x,y,t) by means of an optical-flow-based algorithm, provide the topology of the flow at the wall and feed a physics-based criterion for the identification of flow separation S(y,t) and reattachment R(y,t) which fulfill, in average, a ground-truth validation. The obtained S(y,t) is composed of several manifolds that extend spanwise from saddle points to converging nodes via the saddles unstable manifold, while, at least at higher AoA, manifolds that compose R(y,t) move from diverging nodes to saddle points via the saddles stable manifolds. The trigger of a wedge-shaped event by a rising Omega-shaped vortex in the reverse LSB flow is captured and described.

Item URL in elib:https://elib.dlr.de/125789/
Document Type:Article
Additional Information:Published Online: 13 December 2018, Article:13, ISSN:1432-1114 (Online)
Title:Skin friction and coherent structures within a laminar separation bubble
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Miozzi, Massimomassimo.miozzi (at) cnr.itUNSPECIFIED
Capone, Alessandroalessandro.capone (at) uniud.itUNSPECIFIED
Costantini, MarcoMarco.Costantini (at) dlr.dehttps://orcid.org/0000-0003-0642-0199
Fratto, Lorenzofrattolorenzo (at) gmail.comUNSPECIFIED
Klein, Christianchristian.klein (at) dlr.dehttps://orcid.org/0000-0001-7592-6922
Di Felice, Fabiofabio.difelice (at) cnr.itUNSPECIFIED
Date:January 2019
Journal or Publication Title:Experiments in Fluids
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:60
DOI :10.1007/s00348-018-2651-8
Page Range:pp. 1-25
Publisher:Springer
Series Name:Springer Verlag
ISSN:0723-4864
Status:Published
Keywords:Temperature-Sensitive Paint, Skin Friction, Laminar Separation Bubble
Institution:Deutsches Zentrum für Luft- und Raumfahrt e.V.
Department:AS-EXV
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: Micknaus, Ilka
Deposited On:10 Jan 2019 01:41
Last Modified:06 Sep 2019 15:25

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