Breadcrumb
Oblique laminar-turbulent interfaces in wall-bounded shear flows
Thu 31 January 2013, 14:00
Yohann Duguet
Laboratoire d'Informatique pour la Mécanique et les Sciences de l'Ingénieur (LIMSI-CNRS)
Organiser: Mark Woodhouse
ABSTRACT
The onset of transition to turbulence in subcritical wall-bounded flows is characterised by large-scale localised structures such as turbulent spots or turbulent stripes. Interestingly, the laminar-turbulent interfaces associated with these structures always display obliqueness with respect to the mean direction of the flow. We will attempt to explain this phenomenon using an assumption of scale separation between large and small scales, and we can show analytically that the corresponding laminar-turbulent interfaces are always oblique with respect to the mean direction of the flow. In the case of plane Couette flow, the mismatch between the streamwise flow rates near the boundaries of a single turbulence patch generates a large-scale flow with a non-zero spanwise component. Advection of the small-scale turbulent fluctuations by the corresponding large-scale flow distorts the shape of the turbulence patch and is responsible for its oblique growth. This mechanism can be easily extended to other flows such as Plane Poiseuille flow or Taylor-Couette flow.