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REACTIVE CONTROL OF BYPASS TRANSITION IN A WING BOUNDARY LAYER
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-1766-5557
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-5913-5431
Saab Aeronautics, Bröderna Ugglas gata, SE-58188, Linköping, Sweden, Bröderna Ugglas gata.
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Number of Authors: 52022 (English)In: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022, International Council of the Aeronautical Sciences , 2022, p. 3037-3047Conference paper, Published paper (Refereed)
Abstract [en]

This investigation deals with the numerical implementation of a data-driven method for reactive control of the boundary-layer over a NACA0008 airfoil. The aim of this work is to evaluate the performance of controller in damping the flow disturbances and its efficiency in delaying laminar-turbulent transition. We focus our attention on the bypass transition scenario caused by free-stream turbulence. In this scenario, the perturbations in the wing boundary-layer develop into streaky structures. We show that this data-driven method is effective in decreasing the wall shear stress and disturbance energy at the objective location, and this damping is sustained downstream of the objective location. However, further downstream, the fluctuations grow again reaching amplitudes similar to those in the uncontrolled case.

Place, publisher, year, edition, pages
International Council of the Aeronautical Sciences , 2022. p. 3037-3047
Keywords [en]
Bypass transition, Flow control
National Category
Aerospace Engineering
Identifiers
URN: urn:nbn:se:kth:diva-333313Scopus ID: 2-s2.0-85159580713OAI: oai:DiVA.org:kth-333313DiVA, id: diva2:1784931
Conference
33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022, Stockholm, Sweden, Sep 4 2022 - Sep 9 2022
Note

Part of ISBN 9781713871163

QC 20230801

Available from: 2023-08-01 Created: 2023-08-01 Last updated: 2024-05-20Bibliographically approved
In thesis
1. Numerical investigations of bypass transition and its control
Open this publication in new window or tab >>Numerical investigations of bypass transition and its control
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the laminar-turbulent transition process in boundary layers induced by free-stream turbulence (FST), commonly referred to as bypass transition. The investigation has been carried out using direct numerical simulations (DNS), stability analysis, and control theory. The various aspects of bypass transition considered in this work can be grouped into two categories: open and closed-loop dynamics. 

The open-loop dynamics span from the inception to the breakdown of instabilities, driving the flow from a laminar to a turbulent state. A broader understanding of this process could inspire new and more accurate models for transition prediction, which is of great interest in many engineering applications. In this context, stability theory provides an excellent framework to study the pre-transitional flow. This work has confirmed the relevance of optimal disturbance theory in realistic flow conditions, and how its inexpensive computations can provide valuable information regarding the most 'dangerous' disturbances in terms of their amplification. The key role of streak secondary instabilities in bypass transition has also been studied. They constitute the main cause of transition in a flat plate simulation considering realistic wind tunnel conditions. By comparing the secondary instabilities leading to breakdown in different geometries and FST compositions, it has been found that their hosting streaks feature similar aspect ratios, regardless of their streamwise position. An explanation for this apparent size preference has been provided based on optimal growth and energy propagation due to non-linear interactions.

The closed-loop dynamics address how new inputs can steer the system to a desired state based on operational information extracted from the system. In boundary layers, delaying transition is an attractive idea for energy savings due to the lower drag associated with a laminar state. This work explores this possibility with the use of control theory in reduced-order models constructed solely on input/output data from DNS. The methods are restricted to being equally feasible in experiments. Here, streak attenuation is successfully achieved based only on wall measurements and wall localised actuation. It has been shown that the dissimilar performances regarding transition delay are connected to the controller's capabilities of acting on breaking streaks.

Abstract [sv]

Denna avhandling behandlar den laminära-turbulenta övergångsprocessen i gränsskikt inducerad av friströmsturbulens (FST), vanligen kallad bypass-transition. Studien har genomförts med hjälp av direkta numeriska simuleringar (DNS), stabilitetsanalys och reglerteknik. Två typer av bypass-transition beaktas, omslagsprocessen utan reglerteknisk påverkan och med användning av reglerteknik. 

Omslagsprocessen utan användning av reglerteknik handlar till stor del om hur instabiliteter växer och bryter ner strömningen till turbulens.  En bredare förståelse av denna process kan resultera i bättre metoder för att förutsäga laminärt-turbulent omslag, vilket är av stort intresse i många tekniska tillämpningar. I detta sammanhang ger stabilitetsteori ett utmärkt ramverk för att studera strömningen före omslaget sker. Vårt arbete har bekräftat relevansen av sk ``optimal störningsteori'' i realistiska situationer, och hur de kan ge värdefull information om de mest ``farliga'' störningarna. Nyckelrollen av sekundärinstabiliteter har också studerats. De utgör huvudorsaken till övergången till turbulens för strömningen över vingar och plana plattor där strömningen i friströmmen innehåller tillräckligt med turbulens. Genom att jämföra sekundärinstabiliteterna som leder till sammanbrott i olika geometrier har det visat sig att långa strukturer av hög- och låghastighetsstråk med liknande förhållande mellan spännvidds och vertikal skalor är associerade med sammanbrott till turbulens. En förklaring för denna storlekspreferens baseras på optimal tillväxt tillsammans med icke-linjär interaktion mellan stråk med olika spännvidds skalor. 

Med användning av reglerteknik adresserar vi hur aktuatorer kan styra systemet till ett önskat tillstånd baserat på information som via mätningar extraherats från systemet. I gränsskiktströmning är man intresserad av att fördröja övergång från laminärt till turbulent tillstånd för att åstadkomma energibesparingar genom det lägre motståndet ett laminärt tillstånd har. Detta arbete undersöker möjligheten att använda reglerteknik tillsammans med enkla modeller baserade på analys av på in/utdata från direktsimuleringarna. Metoderna är beskaffade så att de skulle kunna anvädas i en experimentellt. Vi dämpar de stråkstrukturer som finns i gränsskiktsströmningen framgångsrikt. Fördröjningen av laminär-turbulent omslag är kopplade till möjligheten att begränsa amplituden på de stråk som har störst sannolikhet att bryta samman till turbulens via sekundärinstabiliteter. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2024. p. 44
Series
TRITA-SCI-FOU ; 2024:27
Keywords
boundary layers, stability, laminar-turbulent transition, reduced order model, flow control, direct numerical simulations, gränsskikt, stabilitet, laminär-turbulent omslag, modellreduktion, strömningskontroll, direkt numerisk simulering
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-346610 (URN)978-91-8040-948-3 (ISBN)
Public defence
2024-06-14, U1, Brinellvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2024-05-21 Created: 2024-05-20 Last updated: 2024-06-13Bibliographically approved

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Alarcón, José FaúndezSasaki, KenzoHanifi, ArdeshirHenningson, Dan S.

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