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Modeling for the topology of coherent structures within a laminar separation bubble

Miozzi, Massimo and Klein, Christian and Di Felice, Fabio and Costantini, Marco (2019) Modeling for the topology of coherent structures within a laminar separation bubble. In: 15th International Conference on Fluid Control, Measurements and Visualization (FLUCOME 2019) (168), 1 - 2. University of Naples Federico II. 15th International Conference on Fluid Control, Measurements and Visualization (FLUCOME 2019), 27.-30. Mai 2019, Neapel, Italien.

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Official URL: https://flucome2019.unina.it/e-book/FLUCOME2019.html

Abstract

The large variation of lift and drag around a lifting profile, as a consequence of the flow transition and/or separation, has been widely investigated in recent years. The accurate characterization of the flow separation and the laminar-turbulent transition evolution is a primary input for surface design and flow control, while accurate measurements resolved in space and time are still not available. To this aim, the skin-friction estimation provides useful insights in the understanding of laminar and turbulent boundary layer evolution and in the investigation of separation and laminar-turbulent transition. Here we deal this subject with an experimental approach whose focus is on the skin-friction data derived from time histories of temperature maps obtained using Temperature Sensitive Paint (TSP). We report about a NACA 0015 hydrofoil tested in a water cavitating tunnel (CEIMM facility) at angles of attack AoA between 1° and 10° and Re = 180000, observed at a frame rate of 1 kHz via a Photron SAX camera. A region of recirculating flow was identified confined between laminar separation and turbulent reattachment points, which is commonly referred to as Laminar Separation Bubble (LSB). We extract wall quantities which allow for a topological description of the flow at the wall and shed a light in complex interactions of flow structures with the surface. The focus is placed on the topology of the coherent structures that appear in the reverse flow inside the recirculating region at different AoA. We conjecture that disturbances from the shear layer, which develop before the incoming laminar-turbulent transition, appear as impinging jets in the reverse flow region. Then, by adopting a potential vortex model as corresponding induced flow field and coupling it with a model of the flow in the reverse region, the raise, development and set of the associated coherent structures at the wall is described and compared with the corresponding skin friction topology extracted from temperature maps. Test cases are shown about the interaction of such impinging jets against the separation line at AoA = 10° and the development of omega-shaped, hairpin-like vortices in the reverse flow region at AoA = 3°. These flow structures appear opposite to the classical hairpin scheme of turbulent boundary layer, i.e. faster flow far from the wall is pushed down against the separation line towards the leading edge, thus inducing intermittent, highly energetic bursting phenomena involving the LSB dynamics. Further examples of coherent structures will be reported in the final contribution.

Item URL in elib:https://elib.dlr.de/127749/
Document Type:Conference or Workshop Item (Speech)
Additional Information:Extended Abstract ID: 168. FLUCOME2019-168.
Title:Modeling for the topology of coherent structures within a laminar separation bubble
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Miozzi, Massimomassimo.miozzi (at) cnr.itUNSPECIFIED
Klein, Christianchristian.klein (at) dlr.dehttps://orcid.org/0000-0001-7592-6922
Di Felice, Fabiofabio.difelice (at) cnr.itUNSPECIFIED
Costantini, Marcomarco.costantini (at) dlr.dehttps://orcid.org/0000-0003-0642-0199
Date:May 2019
Journal or Publication Title:15th International Conference on Fluid Control, Measurements and Visualization (FLUCOME 2019)
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Page Range:1 - 2
Editors:
EditorsEmail
Cardone, Gennarogcardone@unina.it
Publisher:University of Naples Federico II
Series Name:E-Book Proceedings
Status:Published
Keywords:Laminar/Turbulent flows; Heat and mass transfer; Temperature-sensitive paints; Image processing
Event Title:15th International Conference on Fluid Control, Measurements and Visualization (FLUCOME 2019)
Event Location:Neapel, Italien
Event Type:international Conference
Event Dates:27.-30. Mai 2019
Organizer:University of Naples Federico II
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:26 Jun 2019 11:12
Last Modified:31 Jul 2019 20:25

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