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Numerical studies of the instability and breakdown of a boundary-layer low-speed streak
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.ORCID iD: 0000-0002-4346-4732
2007 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 26, no 1, 64-82 p.Article in journal (Refereed) Published
Abstract [en]

The experimental configuration in [M. Asai, M. Minagawa, M. Nishioka, The instability and breakdown of a near-wall low-speed streak, J. Fluid Mech. 455 (2002) 289-314] is numerically reproduced in order to examine the instability of a single low-speed streak in a laminar boundary layer and to investigate the resulting generation of coherent structures. Such a configuration is chosen since the experimental data show that the two instability modes, varicose and sinuous, are of comparable strength. The instability characteristics are retrieved from the simulation of the flow impulse response. The varicose instability is associated to higher frequencies and lower group velocities than those of the sinuous modes. The latter are less affected by the diffusion of the streak mean shear and are amplified for a longer streamwise distance. Analysis of the perturbation kinetic energy production reveals that both the varicose and the sinuous instability are driven by the work of the Reynolds stress against the wall-normal shear of the streak. The base flow considered here therefore presents an exception to the common knowledge, supported by several previous studies, that the sinuous instability is associated to the streak spanwise shear. The vortical structures at the late stage of the varicose breakdown are identified from the numerical data. By comparing them with those pertaining to other transition scenarios, it is confirmed that streaks and streamwise vortices are universal features of boundary layer transition.

Place, publisher, year, edition, pages
2007. Vol. 26, no 1, 64-82 p.
Keyword [en]
boundary layers, transition to turbulence, stability, streamwise streaks, hairpin vortices, near-wall turbulence, shear flows, localized disturbances, channel flow, transition, simulation, growth, vortex, waves, zero
URN: urn:nbn:se:kth:diva-16312DOI: 10.1016/j.euromechflu.2006.04.008ISI: 000243293000006ScopusID: 2-s2.0-33845336109OAI: diva2:334354
QC 20100525Available from: 2010-08-05 Created: 2010-08-05Bibliographically approved

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