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Complexity of localised coherent structures in a boundary-layer flow
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
LIMSI-CNRS, Université Paris-Sud.
Fachbereich Physik, Philipps-Universität Marburg.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-9627-5903
Show others and affiliations
2014 (English)In: The European Physical Journal E Soft matter, ISSN 1292-8941, E-ISSN 1292-895X, Vol. 37, no 32Article in journal (Refereed) Published
Abstract [en]

We study numerically transitional coherent structures in a boundary-layer flow with homogeneous suction at the wall (the so-called asymptotic suction boundary layer ASBL). The dynamics restricted to the laminar-turbulent separatrix is investigated in a spanwise-extended domain that allows for robust localisation of all edge states. We work at fixed Reynolds number and study the edge states as a function of the streamwise period. We demonstrate the complex spatio-temporal dynamics of these localised states, which exhibits multistability and undergoes complex bifurcations leading from periodic to chaotic regimes. It is argued that in all regimes the dynamics restricted to the edge is essentially low-dimensional and non-extensive.

Place, publisher, year, edition, pages
2014. Vol. 37, no 32
Keyword [en]
boundary layers, nonlinear dynamical systems, edge states, multistability, period doubling, Pomeau-Manneville intermittency
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-141345DOI: 10.1140/epje/i2014-14032-3ISI: 000335160300002Scopus ID: 2-s2.0-84901942755OAI: oai:DiVA.org:kth-141345DiVA: diva2:696400
Note

QC 20140602

Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Transition to turbulence in the asymptotic suction boundary layer
Open this publication in new window or tab >>Transition to turbulence in the asymptotic suction boundary layer
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this thesis is on the numerical study of subcritical transition to turbulence in the asymptotic suction boundary layer (ASBL). Applying constant homogeneous suction prevents the spatial growth of the boundary layer, granting access to the asymptotic dynamics. This enables research approaches which are not feasible in the spatially growing case.

In a first part, the laminar–turbulent separatrix of the ASBL is investigated numerically by means of an edge-tracking algorithm. The consideration of spanwise-extended domains allows for the robust localisation of the attracting flow structures on this separatrix. The active part of the identified edge states consists of a pair of low- and high-speed streaks, which experience calm phases followed by high energy bursts. During these bursts the structure is destroyed and re-created with a shift in the spanwise direction. Depending on the streamwise extent of the domain, these shifts are either regular in direction and distance, and periodic in time, or irregular in space and erratic in time. In all cases, the same clear regeneration mechanism of streaks and vor- tices is identified, bearing strong similarities with the classical self-sustaining cycle in near-wall turbulence. Bifurcations from periodic to chaotic regimes are studied by varying the streamwise length of the (periodic) domain. The resulting bifurcation diagram contains a number of phenomena, e.g. multistability, intermittency and period doubling, usually investigated in the context of low-dimensional systems.

The second part is concerned with spatio–temporal aspects of turbulent ASBL in large domains near the onset of sustained turbulence. Adiabatically decreasing the Reynolds number, starting from a fully turbulent state, we study low-Re turbulence and events leading to laminarisation. Furthermore, a robust quantitative estimate for the lowest Reynolds number at which turbulence is sustained is obtained at Re  270.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. viii, 27 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2014:03
Keyword
boundary layers, instability, laminar-turbulent transition, dynamical systems, edge states, near-wall turbulence, laminarisation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-141344 (URN)978-91-7595-022-8 (ISBN)
Presentation
2014-02-28, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20140213

Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2014-02-13Bibliographically approved
2. Edge states and transition to turbulence in boundary layers
Open this publication in new window or tab >>Edge states and transition to turbulence in boundary layers
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this thesis is the numerical study of subcritical transition to turbulence in boundary-layer flows. For the most part, boundary layers with uniform suction are considered. Constant homogeneous suction counteracts the spatial growth of the boundary layer, rendering the flow parallel. This enables research approaches which are not feasible in the context of spatially developing flows.

In the first part, the laminar–turbulent separatrix of the asymptotic suction boundary layer (ASBL) is investigated numerically by means of an edge-tracking algorithm. The obtained edge states experience recurrent dynamics, going through calm and bursting phases. The self-sustaining mechanism bears many similarities with the classical regeneration cycle of near-wall turbulence. The recurrent simple structure active during calm phases is compared to the nucleation of turbulence events in bypass transition originating from delocalised initial conditions. The implications on the understanding of the bypass-transition process and the edge state's role are discussed.

Based on this understanding, a model is constructed which predicts the position of the nucleation of turbulent spots during free-stream turbulence induced transition in spatially developing boundary-layer flow. This model is used together with a probabilistic cellular automaton (PCA), which captures the spatial spreading of the spots, correctly reproducing the main statistical characteristics of the transition process.

The last part of the thesis is concerned with the spatio-temporal aspects of turbulent ASBL in extended numerical domains near the onset of sustained turbulence. The different behaviour observed in ASBL, i.e. absence of sustained laminar–turbulent patterns, which have been reported in other wall-bounded flows, is associated with different character of the large-scale flow. In addition, an accurate quantitative estimate for the lowest Reynolds number with sustained turbulence is obtained

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. 45 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2016:08
Keyword
boundary layer, transition to turbulence, direct numerical simulation, edge state, free-stream turbulence, bypass transition, probabilistic cellular automaton, turbulence at the onset, laminar–turbulent coexistence, laminarisation
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-186038 (URN)978-91-7595-977-1 (ISBN)
Public defence
2016-05-19, F3, Lindstedtsvägen 26, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20160429

Available from: 2016-04-29 Created: 2016-04-29 Last updated: 2016-05-03Bibliographically approved

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Schlatter, PhilippHenningson, Dan Stefan

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