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Boundary layer stabilization using free-stream vortice
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-3251-8328
2015 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 764, R2- p.Article in journal (Refereed) Published
Abstract [en]

In this numerical investigation we explore the possibility of applying free-stream vortices as a passive flow control method for delaying the transition to turbulence. The work is motivated by previous experimental studies demonstrating that stable streamwise boundary layer (BL) streaks can attenuate both two-and three-dimensional disturbances inside the BL, leading to transition delay, with the implication of reducing skin-friction drag. To date, successful control has been obtained using physical BL modulators mounted on the surface in order to generate stable streaks. However, surface mounted BL modulators are doomed to failure when the BL is subject to free-stream turbulence (FST), since a destructive interaction between the two is inevitable. In order to tackle free-stream disturbances, such as FST, a smooth surface is desired, which has motivated us to seek new methods to induce streamwise streaks inside the BL. A first step, in a systematic order, is taken in the present paper to prove the control idea of generating free-stream vortices for the attenuation of ordinary Tollmien-Schlichting waves inside the BL. In this proof-of-concept study we show that, by applying a spanwise array of counter-rotating free-stream vortices, inducing streamwise BL streaks further downstream, it is possible to alter the BL stability characteristics to such a degree that transition delay may be accomplished. For the demonstration we use direct numerical simulations along with stability analysis.

Place, publisher, year, edition, pages
2015. Vol. 764, R2- p.
Keyword [en]
boundary layer control, drag reduction, transition to turbulence
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-160373DOI: 10.1017/jfm.2014.731ISI: 000348128700002ScopusID: 2-s2.0-84927138962OAI: diva2:791225
EU, European Research Council

QC 20150227

Available from: 2015-02-27 Created: 2015-02-19 Last updated: 2015-02-27Bibliographically approved

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Fransson, Jens H. M.
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