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Decomposition of the mean friction drag in adverse-pressure-gradient turbulent boundary layers
Shanghai Jiao Tong Univ, Sch Aeronaut & Astronaut, Shanghai 200240, Peoples R China..
Shanghai Jiao Tong Univ, Sch Aeronaut & Astronaut, Shanghai 200240, Peoples R China..
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. (SimEx FLOW)
KTH, School of Engineering Sciences (SCI), Engineering Mechanics. (SimEx FLOW)
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2020 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, no 11, article id 114608Article in journal (Refereed) Published
Abstract [en]

In this study, we exploit the Renard-Deck identity [J. Fluid Mech. 790, 339 (2016)] to decompose the mean friction drag in adverse-pressure-gradient turbulent boundary layers (APG-TBLs) into three components, associated with viscous dissipation, turbulence kinetic energy production, and spatial growth of the flow, respectively. We consider adverse-pressure-gradient turbulent boundary layers developing on flat plates and airfoils, with friction Reynolds numbers in the range 200 < Re-tau < 2000, and with Rotta-Clauser pressure-gradient parameters (beta) ranging from 0 to 50. The effects of Reynolds number, adverse pressure gradient, and the pressure-gradient history on the contributing components are individually investigated, and special attention is paid to the comparisons with zero-pressure-gradient turbulent boundary layers (ZPG-TBLs). Our results indicate that the inner peaks of the dissipation and production terms are located at y(+) approximate to 6 and y(+) approximate to 16.5, respectively, and their outer peaks scale with the 99% boundary-layer thickness (delta(99)), i.e., y/delta(99) approximate to 0.7 and 0.53, respectively. These results are independent of the friction Reynolds number, the magnitude of beta, and its development history. Moreover, the spatial-growth component is negative in the investigated APG-TBLs, and its magnitude increases with beta.

Place, publisher, year, edition, pages
American Physical Society (APS) , 2020. Vol. 5, no 11, article id 114608
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-287416DOI: 10.1103/PhysRevFluids.5.114608ISI: 000590413100006Scopus ID: 2-s2.0-85097581154OAI: oai:DiVA.org:kth-287416DiVA, id: diva2:1509961
Note

QC 20201215

Available from: 2020-12-15 Created: 2020-12-15 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
2. Study of adverse-pressure-gradient effects on a flat-plate boundary layer at high Reynolds numbers
Open this publication in new window or tab >>Study of adverse-pressure-gradient effects on a flat-plate boundary layer at high Reynolds numbers
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
En studie av effekter av negativ tryckgradient på gränsskiktet över en plan platta vid höga Reynolds-tal
Abstract [en]

Turbulent boundary layers are present in many aspects of life, from the weather and wind currents to transportation, production of energy or mixing processes. Understanding turbulent motions can allow for an improvement and development of technical devices, techniques or diagnosis of phenomena where a fluid flow is in the turbulent regime. From the economical and environmental perspectives, knowledge of turbulent boundary layers may help to reduce the drag on aerodynamic surfaces in transportation, thus leading to a reduction in fuel consumption and emissions. It is also possible to enhance the production of energy from wind sources or the harvest of tidal energy. Otherturbulent motions that have recently impacted society are those related to diffusion such as the transport of aerial diseases, or the motions of air in the respiratory system. In all those examples, external pressure gradients or those produced by the curvature of wall surfaces affect the turbulent structures and thus, the outputs that we study such as drag, transport of substances, energetic output, etc. A relevant case is that of adverse pressure gradient, which enhances the wall-normal convection and redistributes the turbulent energy across the turbulent boundary later. In this work, we study a canonical case of an adverse-pressure-gradient turbulent boundary layer, which is the flow over a flat plate, under near-equilibrium adverse-pressure-gradient conditions. We have extended the previous datasets on flat-plate boundary layers under adverse pressure gradients which were obtained at low Reynolds numbers, with a new numerical simulation reaching high Reynolds numbers, comparable to those of experimental campaigns. This new data set allowed us to study both adverse-pressure-gradient and Reynolds-number effects, where the thicker boundary layer exhibits a clear separation of turbulent scales. The influence of the size of the domain and the wider turbulent scales are analyzed through a set of turbulent channel-flow simulations and the spectral analysis of the Reynolds stresses in high Reynolds numbers turbulent boundary layers. The impact of the wider scales was analyzed and scaling factors were found for different regions of the spectra of the Reynolds stresses. In particular, we propose a new scaling for the energy of the small scales that have been advected to the outer region of the boundary layer.

Place, publisher, year, edition, pages
Sweden 2022: KTH Royal Institute of Technology, 2022. p. 177
Series
TRITA-SCI-FOU ; 2022:47
Keywords
Turbulence, simulations, turbulent boundary layers, adverse pressure gradients.
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-319942 (URN)978-91-8040-353-5 (ISBN)
Public defence
2022-11-03, F3, Lindstedtsvägen 26, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 221012

Available from: 2022-10-12 Created: 2022-10-11 Last updated: 2022-10-24Bibliographically approved

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Atzori, MarcoPozuelo, RamonSchlatter, PhilippVinuesa, Ricardo

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