Turbulent spots in the asymptotic suction boundary layer
2007 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 584, 397-413 p.Article in journal (Refereed) Published
Amplitude thresholds for transition of localized disturbances, their breakdown to turbulence and the development of turbulent spots in the asymptotic suction boundary layer are studied using direct numerical simulations. A parametric study of the horizontal scales of the initial disturbance is performed and the disturbances that lead to the highest growth under the conditions investigated are used in the simulations. The Reynolds-number dependence of the threshold amplitude of a localized disturbance is investigated for 500 <= Re <= 1200, based on the free-stream velocity and the displacement thickness. It is found that the threshold amplitude scales as Re-1.5 for the considered Reynolds numbers. For Re <= 367, the localized disturbance does not lead to a turbulent spot and this provides an estimate of the critical Reynolds number for the onset of turbulence. When the localized disturbance breaks down to a turbulent spot, it happens through the development of hairpin and spiral vortices. The shape and spreading rate of the turbulent spot are determined for Re = 500, 800 and 1200. Flow visualizations reveal that the turbulent spot takes a bullet-shaped form that becomes more distinct for higher Reynolds numbers. Long streaks extend in front of the spot and in its wake a calm region exists. The spreading rate of the turbulent spot is found to increase with increasing Reynolds number.
Place, publisher, year, edition, pages
2007. Vol. 584, 397-413 p.
plane poiseuille flow, adverse pressure-gradient, free-stream turbulence, couette-flow, localized disturbances, subcritical transition, numerical simulations, bypass transition, channel flows, shear flows
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-8903DOI: 10.1017/S0022112007006544ISI: 000249137500018ScopusID: 2-s2.0-34547787137OAI: oai:DiVA.org:kth-8903DiVA: diva2:14384
Uppdaterad från manuskript till artikel: 20101025.
QC 201010252005-12-082005-12-082010-10-25Bibliographically approved