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Streak interactions and breakdown in boundary layer flows
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.ORCID iD: 0000-0002-4346-4732
2008 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 20, no 2Article in journal (Refereed) Published
Abstract [en]

The objective of this paper is to show that the interaction of streamwise velocity streaks of finite length can lead to turbulent breakdown in the flat-plate boundary layer flow. The work is motivated by previous numerical and experimental studies of transitional flows where the high-frequency oscillations leading to turbulence are seen to form in the region of strongest shear induced by streaks in relative motion. Therefore, a model for the interaction of steady and unsteady (i.e., slowly moving in the spanwise direction) spanwise periodic streaks is proposed. The interaction of two subsequent streaks is investigated for varying collision parameters. In particular, the relative spanwise position and angle are considered. The results show that the interaction is able to produce both a symmetric and asymmetric breakdown without the need for additional random noise from the main stream. Velocity structures characteristic of both scenarios are analyzed. Hairpin and A vortices are found in the case of symmetric collision between a low-speed region and an incoming high-speed streak, when a region of strong wall-normal shear is induced. Alternatively, when the incoming high-momentum fluid is misaligned with the low-speed streak in front, single quasi-streamwise vortices are identified. Despite the different symmetry at the breakdown, the detrimental interaction involves for both cases the tail of a low-speed region and the head of a high-speed streak. Further, the breakdown appears in both scenarios as an instability of three-dimensional shear layers formed between the two streaks. The streak interaction scenario is suggested to be of relevance for turbulence production in wall-bounded flows.

Place, publisher, year, edition, pages
2008. Vol. 20, no 2
Keyword [en]
near-wall turbulence, self-sustaining process, low-speed streak, streamwise streaks, channel flow, shear flows, coherent structures, instability, transition, stability
URN: urn:nbn:se:kth:diva-17387DOI: 10.1063/1.2838594ISI: 000254141600020ScopusID: 2-s2.0-40449129137OAI: diva2:335431
QC 20100525Available from: 2010-08-05 Created: 2010-08-05Bibliographically approved

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