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Characterization of turbulent coherent structures in square duct flow
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-6570-5499
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-9627-5903
2018 (English)In: Journal of Physics: Conference Series, Institute of Physics Publishing (IOPP), 2018, Vol. 1001, no 1Conference paper, Published paper (Refereed)
Abstract [en]

This work is aimed at a first characterization of coherent structures in turbulent square duct flows. Coherent structures are defined as connected components in the domain identified as places where a quantity of interest (such as Reynolds stress or vorticity) is larger than a prescribed non-uniform threshold. Firstly, we qualitatively discuss how a percolation analysis can be used to assess the effectiveness of the threshold function, and how it can be affected by statistical uncertainty. Secondly, various physical quantities that are expected to play an important role in the dynamics of the secondary flow of Prandtl's second kind are studied. Furthermore, a characterization of intense Reynolds-stress events in square duct flow, together with a comparison of their shape for analogous events in channel flow at the same Reynolds number, is presented.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018. Vol. 1001, no 1
Series
Journal of Physics: Conference Series, ISSN 1742-6588 ; 1001
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-238245DOI: 10.1088/1742-6596/1001/1/012008ISI: 000454926900008Scopus ID: 2-s2.0-85046084236OAI: oai:DiVA.org:kth-238245DiVA, id: diva2:1263768
Conference
3rd Madrid Summer School on Turbulence, School of Aeronautics of the Universidad Politecnica de MadridMadrid, Spain, 29 May 2017 through 30 June 2017
Funder
EU, European Research CouncilSwedish Research CouncilSwedish Foundation for Strategic Research , BD15-0082Knut and Alice Wallenberg Foundation, BD15-0082Swedish e‐Science Research Center
Note

QC 20181116

Available from: 2018-11-16 Created: 2018-11-16 Last updated: 2024-03-15Bibliographically approved
In thesis
1. Coherent structures and control in wall-bounded turbulent flows
Open this publication in new window or tab >>Coherent structures and control in wall-bounded turbulent flows
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is concerned with two distinct topics related to the study of wall-bounded turbulence: the connection between instantaneous three-dimensional coherent structures and mean-flow properties, and the development and analysis of pre-determined control techniques for adverse-pressure-gradient boundary layers.

We examined regions with intense velocity fluctuations in various flowcases. In turbulent ducts, we found that, on the one hand, the specific geometry of the domain has measurable effects on the shape and dimensions of these structures. On the other hand, however, their contribution to the mean secondary flow, which is the main distinguishing feature of turbulent ducts, is not particularly significant. Intense events contribute to the mean velocity in a similar way as in periodic channels, where the secondary flow is not present. Studying adverse- and zero-pressure-gradient turbulent boundary layers, we found that there are qualitative differences in how intense-fluctuation events affect the mean properties of these two flows. Our results suggest that coherent structures may help to explain history effects and development of the outer peak in wall-tangential fluctuations. An efficient algorithm for percolation analysis and an in-situ adaptor for the simulation code Nek5000 and the visualization software Paraview have also been developed as part of this effort.

We also created a new dataset including various combinations of uniform blowing and suction applied to a NACA4412 airfoil, employing high-fidelity numerical simulations and turbulence models. There are significant discrepancies between how the control interacts with turbulence under different pressure-gradient conditions, which illustrates the need of considering test cases as similar as possible to operative conditions in control studies. We also found that the most promising control configuration for a wide range of Reynolds numbers is uniform blowing applied to the airfoil pressure side. In particular, it reduces both pressure and skin-friction drag, resulting in higher aerodynamic efficiency and potential net-energy saving when the actuation cost is included.

Abstract [sv]

Denna avhandling handlar om två olika ämnen relaterade till studien av väggbunden turbulens: sambandet mellan momentana tredimensionella koherenta strukturer och medelflödesegenskaper och utveckling och analys av förutbestämda styrtekniker för negativ tryckgradientgräns skikten. 

Vi undersökte regioner med intensiva hastighetsfluktuationer i olika studiefall. I turbulenta kanaler fann vi att å ena sidan har domänens specifika geometri mätbara effekter på formen och dimensionerna hos dessa strukturer. Å andra sidan är deras bidrag till det genomsnittliga sekundära flödet, som är huvudfunktionen i turbulenta kanaler, inte särskilt signifikant. Intensiva händelser bidrar till medelhastigheten på ett liknande sätt som i periodiska kanalströmmar, där sekundärflödet inte finns. När vi studerade ogynnsamma och nolltryckgradient turbulenta gränsskikt, fann vi att det finns kvalitativa skillnader i hur intensiva fluktuationshändelser påverkar medelegenskaperna för dessa två flöden. Våra resultat tyder på att sammanhängande strukturer kan hjälpa till att förklara historiska effekter och utveckling av den yttre toppen i väggtangentiella fluktuationer. En effektiv algoritm för perkoleringsanalys och en adapter på plats för simuleringskoden Nek5000 och visualiseringsmjukvaran Paraview har också utvecklats som en del av detta arbete.

Vi skapade en ny dataset inklusive olika kombinationer av enhetlig blåsning och sugning applicerad på en NACA4412-flygplatta, med användning av högkvalitativa numeriska simuleringar och turbulensmodeller. Det finns signifikanta skillnader mellan hur kontrollen interagerar med turbulens under olika tryckgradientförhållanden, vilket illustrerar behovet av att betrakta testfall som liknar operativa förhållanden i kontrollstudier. Vi fann också att den mest lovande kontrollkonfigurationen för ett brett spektrum av Reynolds-nummer är enhetlig blåsning som appliceras på flygplattans trycksida. I synnerhet minskar det både tryck- och hudfriktionsdragningar, vilket resulterar i högre aerodynamisk effektivitet och potentiell nettoenergibesparing när manöverkostnaden beräknas.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2021. p. 95
Series
TRITA-SCI-FOU ; 2021:23
Keywords
Turbulent boundary layers, numerical simulations, coherent structures, predetermined flow control., Turbulenta gränsskikt, numeriska simuleringar, koherenta strukturer, förutbestämd flödeskontroll
National Category
Mechanical Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-295682 (URN)978-91-7873-917-2 (ISBN)
Public defence
2021-06-14, Live-streaming via Zoom: https://kth-se.zoom.us/j/66964086047, Stockholm, 10:30 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research, BD15-0082
Available from: 2021-05-25 Created: 2021-05-25 Last updated: 2022-07-08Bibliographically approved

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Atzori, MarcoVinuesa, RicardoSchlatter, Philipp

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