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Transition to turbulence in the asymptotic suction boundary layer
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
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 $\approx$ 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 [en]
boundary layers, instability, laminar-turbulent transition, dynamical systems, edge states, near-wall turbulence, laminarisation
##### National Category
Fluid Mechanics and Acoustics
##### Identifiers
ISBN: 978-91-7595-022-8 (print)OAI: oai:DiVA.org:kth-141344DiVA: diva2:696386
##### Presentation
2014-02-28, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:15 (English)
##### Note

QC 20140213

Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2014-02-13Bibliographically approved
##### List of papers
1. Localized edge states in the asymptotic suction boundary layer
Open this publication in new window or tab >>Localized edge states in the asymptotic suction boundary layer
2013 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 717, no R6Article in journal (Refereed) Published
##### Abstract [en]

The dynamics on the laminar-turbulent separatrix is investigated numerically for boundary-layer flows in the subcritical regime. Constant homogeneous suction is applied at the wall, resulting in a parallel asymptotic suction boundary layer (ASBL). When the numerical domain is sufficiently extended in the spanwise direction, the coherent structures found by edge tracking are invariably localized and their dynamics shows bursts that drive a remarkable regular or irregular spanwise dynamics. Depending on the parameters, the asymptotic dynamics on the edge can be either periodic in time or chaotic. A clear mechanism for the regeneration of streaks and streamwise vortices emerges in all cases and is investigated in detail.

##### Keyword
boundary layers, instability, nonlinear dynamical systems
##### National Category
Fluid Mechanics and Acoustics
##### Identifiers
urn:nbn:se:kth:diva-122354 (URN)10.1017/jfm.2013.20 (DOI)000317421600006 ()2-s2.0-84878528716 (Scopus ID)
##### Note

QC 20130522

Available from: 2013-05-22 Created: 2013-05-20 Last updated: 2017-12-06Bibliographically approved
2. Complexity of localised coherent structures in a boundary-layer flow
Open this publication in new window or tab >>Complexity of localised coherent structures in a boundary-layer flow
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.

##### Keyword
boundary layers, nonlinear dynamical systems, edge states, multistability, period doubling, Pomeau-Manneville intermittency
##### National Category
Fluid Mechanics and Acoustics
##### Identifiers
urn:nbn:se:kth:diva-141345 (URN)10.1140/epje/i2014-14032-3 (DOI)000335160300002 ()2-s2.0-84901942755 (Scopus ID)
##### Note

QC 20140602

Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2017-12-06Bibliographically approved
3. Turbulence and laminarisation in the spatially extended asymptotic suction boundary layer
Open this publication in new window or tab >>Turbulence and laminarisation in the spatially extended asymptotic suction boundary layer
##### 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.

22 p.
##### Keyword
Boundary layers, turbulence, amplitude modulation, lamin arisation
##### National Category
Engineering and Technology
##### Identifiers
urn:nbn:se:kth:diva-141346 (URN)
##### Note

QC 20140213

Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2014-02-13Bibliographically approved

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Cite
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