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Global stability of 180-bend pipe flow with mesh adaptivity
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-6712-8944
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.ORCID iD: 0000-0002-8426-4833
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.ORCID iD: 0000-0002-7448-3290
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Institute of Fluid Mechanics (LSTM), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen 91058, Germany.ORCID iD: 0000-0001-9627-5903
2023 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 8, no 11, article id 113903Article in journal (Refereed) Published
Abstract [en]

The global stability of the flow in a spatially developing 180∘-bend pipe with curvature δ=R/Rc=1/3 is investigated by performing direct numerical simulations to understand the underlying transitional mechanism. A unique application of the adaptive mesh refinement technique is used during the stability analysis for minimizing the interpolation and quadrature errors. Independent meshes are created for the direct and adjoint solutions, as well as for the base flow extracted via selective frequency damping. The spectrum of the linearized Navier-Stokes operator reveals a pair of complex conjugate eigenvalues, with frequency f≈0.233. Therefore, the transition is attributed to a Hopf bifurcation that takes place at Reb,cr=2528. A structural sensitivity analysis is performed by extracting the wavemaker. We identify the primary source of instability located on the outer wall, θ≈15 downstream of the bend inlet. This region corresponds to the separation bubble on the outer wall. We thus conclude that the instability is caused by the strong shear resulting from the backflow, similar to the 90-bend pipe flow. We believe that understanding the stability mechanism and characterizing the base flow in bent pipes is crucial for studying various biological flows, like blood vessels. Hence, this paper aims to close the knowledge gap between a 90-bend and toroidal pipes by investigating the transition nature in a 18-bend pipe flow.

Place, publisher, year, edition, pages
American Physical Society (APS) , 2023. Vol. 8, no 11, article id 113903
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-340973DOI: 10.1103/PhysRevFluids.8.113903ISI: 001110146700002Scopus ID: 2-s2.0-85178080751OAI: oai:DiVA.org:kth-340973DiVA, id: diva2:1820277
Note

Not duplicate with DiVA 1757985

QC 20231218

Available from: 2023-12-18 Created: 2023-12-18 Last updated: 2024-02-29Bibliographically approved
In thesis
1. Space-adaptive simulation of transition and turbulence in shear flows
Open this publication in new window or tab >>Space-adaptive simulation of transition and turbulence in shear flows
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Rymdadaptiv simulering av transition och turbulens i skjuvströmning
Abstract [en]

Transitional and turbulent shear flows are ubiquitous, from the boundary layer developing on an aeroplane wing to the flow within the aortic arch. In this thesis, we study wall-bounded and free shear flows through direct numerical simulations. To control numerical errors and represent every flow structure, we implement the adaptive mesh refinement (AMR) technique within a spectral element method code. Using data-driven methods and causality metrics, we explore the fundamental physical mechanisms in various shear flows.

The adaptive mesh refinement technique necessitates a precise evaluation of the committed error. Thus, we compare the local spectral error indicator with the dual-weighted adjoint error estimator. The former ensures a more homogeneous refinement, targeting regions with a high-velocity gradient, while the latter is goal-oriented. However, the adjoint error estimator fails in turbulent flows due to the exponential sensitivity of the adjoint linear solution to any perturbation. Alternatively, we introduce a causality-based error indicator that employs the Shannon transfer entropy, i.e. a causality metric arising from information theory, to establish causal relations between the local solution and a specified quantity of interest.

Using information-theoretic causality, linear global stability analysis and modal decomposition, we investigate transitional and turbulent coherent structures. In turbulent straight pipe flows, the proper orthogonal decomposition is integrated with the Voronoi diagram to automatically discern between wall-attached and detached eddies. In spatially developing bent pipe flows, we employ the proper orthogonal decomposition to examine the swirl switching phenomenon, the origins of which continue to be a topic of debate. In the context of external flows around a cylinder, we explore two configurations: the Flettner rotor, a rotating cylinder in a wall-bounded shear flow, and the stepped cylinder, namely two cylinders of different diameters joined at one extremity. In the first configuration, we analyse the large-scale motion at the base of the rotor and the local vortex shedding suppression. In the second, we provide an in-depth look at structures arising on the junction surface and in the wake. Additionally, we conduct a global stability analysis with a novel AMR-based approach for some of the aforementioned cases.

Abstract [sv]

I denna avhandling studerar vi transitionella och turbulenta skjuvströmningar genom direkta numeriska simuleringar. Med hänsyn till den avgörande rollen av att kontrollera numeriska fel och representera varje skala i rummet, utvecklar, validerar och implementerar vi den adaptiva nätförfiningstekniken inom en spektralelementkod. Med hjälp av data-drivna metoder och mått för kausalitet utforskar vi de grundläggande fysikaliska mekanismerna i olika skjuvströmningar.

Den adaptiva nätförfiningen kräver en noggrann beräkning av det begångna felet. Således jämför vi den lokala spektrala felindikatorn med den felestimatorn från adjunkt-ekvationen. Den förra säkerställer en mer homogen förfining, inriktad på områden med en stor hastighetsgradient, medan den senare är målinriktad. Emellertid misslyckas den adjunkta felestimatorn i turbulenta flöden på grund av den exponentiella känsligheten hos den adjunkta linjära lösningen för turbulenta störningar. Som nytt alternativ introducerar vi en kausalitets-baserad felindikator som använder Shannon-transferentropin, dvs. ett kausalitets-mått som härrör från informationsteori, för att fastställa kausala samband mellan den lokala lösningen och en specificerad kvantitet av intresse.

Med hjälp av detta kausalitets-mått, linjär global stabilitetsanalys och modal dekomposition undersöker vi transitionella och turbulenta koherenta strukturer. I glatta turbulenta rörströmningar använder vi den så kallade proper orthogonal decomposition (POD) med Voronoi-diagrammet för att automatiskt skilja mellan väggnära och yttre virvlar. För strömningsfallet med ett krökt rör med 90 eller 180 grader-vinkel använder vi POD för att undersöka fenomenet swirl switching, vars ursprung fortsatt är oklart i litteraturen. I samband med den externa strömningen runt en cylinder utforskar vi två konfigurationer: Flettner-rotorn, en roterande cylinder i ett gränsskikt och den stegformade cylindern, där två cylindrar med olika diametrar är sammanfogade i ena änden. I den första konfigurationen analyserar vi den storskaliga rörelsen vid rotorns bas och den lokala förändringen av virvelamplituden. I den andra ger vi en djupgående analys av strukturer som uppstår nära mitten och i vaken. Dessutom genomför vi en global stabilitetsanalys med en ny adaptiv metod för att förstå bättre fysiken av de tidigare nämnda fallen.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2024
Series
TRITA-SCI-FOU ; 2024:10
Keywords
Turbulence, global stability, coherent structures, adaptive mesh refinement, Turbulens, global stabilitet, koherenta strukturer, adaptiv nätförfining
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-344052 (URN)978-91-8040-844-8 (ISBN)
Public defence
2024-03-27, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
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Supervisors
Note

QC 240304

Available from: 2024-03-04 Created: 2024-02-29 Last updated: 2024-03-06Bibliographically approved

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Massaro, DanieleLupi, ValerioPeplinski, AdamSchlatter, Philipp

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