Transition of streamwise streaks in zero-pressure-gradient boundary layers

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 op...

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Bibliographic Details
Published in:Journal of fluid mechanics 2002-12, Vol.472, p.229-261
Main Authors: BRANDT, LUCA, HENNINGSON, DAN S.
Format: Article
Language:English
Subjects:
Boundary layer
Boundary layers
BYPASS TRANSITION
CHANNEL FLOW
Creeks & streams
DIRECT NUMERICAL-SIMULATION
Exact sciences and technology
Fluid dynamics
Fundamental areas of phenomenology (including applications)
Hydrodynamic stability
OPTIMAL PERTURBATIONS
Physics
PLANE POISEUILLE FLOW
REYNOLDS-NUMBER
SECONDARY INSTABILITY
SELF-SUSTAINING PROCESS
STABILITY
Transition to turbulence
TURBULENCE
Turbulent flows, convection, and heat transfer
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Summary: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.
ISSN:0022-1120
1469-7645
1469-7645
DOI:10.1017/S0022112002002331