Author:
BRANDT LUCA,HENNINGSON DAN S.
Abstract
A transition scenario initiated by streamwise low- and high-speed streaks in a flat-plate
boundary layer is studied. In many shear flows, the perturbations that show the highest
potential for transient energy amplification consist of streamwise-aligned vortices.
Due to the lift-up mechanism these optimal disturbances lead to elongated streamwise
streaks downstream, with significant spanwise modulation. In a previous investigation
(Andersson et al. 2001), the stability of these streaks in a zero-pressure-gradient
boundary layer was studied by means of Floquet theory and numerical simulations.
The sinuous instability mode was found to be the most dangerous disturbance. We
present here the first simulation of the breakdown to turbulence originating from
the sinuous instability of streamwise streaks. The main structures observed during
the transition process consist of elongated quasi-streamwise vortices located on the
flanks of the low-speed streak. Vortices of alternating sign are overlapping in the
streamwise direction in a staggered pattern. The present scenario is compared with
transition initiated by Tollmien–Schlichting waves and their secondary instability and
by-pass transition initiated by a pair of oblique waves. The relevance of this scenario
to transition induced by free-stream turbulence is also discussed.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
113 articles.
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