Far field of turbulent spots

The proliferation of turbulence in subcritical wall-bounded shear flows involves spatially localised coherent structures. Turbulent spots correspond to finite-time nonlinear responses to pointwise disturbances and are regarded as seeds of turbulence during transition. The rapid spatial decay of the...

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Bibliographic Details
Published in:arXiv.org 2020-09
Main Authors: Kashyap, Pavan V, Duguet, Yohann, Chantry, Matthew
Format: Article
Language:English
Subjects:
Computational fluid dynamics
Decay
Fluid flow
Numerical methods
Reynolds number
Robustness (mathematics)
Shear flow
Spectral methods
Turbulence
Velocity distribution
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Summary:The proliferation of turbulence in subcritical wall-bounded shear flows involves spatially localised coherent structures. Turbulent spots correspond to finite-time nonlinear responses to pointwise disturbances and are regarded as seeds of turbulence during transition. The rapid spatial decay of the turbulent fluctuations away from a spot is accompanied by large-scale flows with a robust structuration. The far field velocity field of these spots is investigated numerically using spectral methods in large domains in four different flow scenarios (plane Couette, plane Poiseuille, Couette-Poiseuille and a sinusoidal shear flow). At odds with former expectations, the planar components of the velocity field decay algebraically. These decay exponents depend only on the symmetries of the system, which here depend on the presence of an applied gradient, and not on the Reynolds number. This suggests an effective two-dimensional multipolar expansion for the far field, dominated by a quadrupolar flow component or, for asymmetric flow fields, by a dipolar flow component.
ISSN:2331-8422
DOI:10.48550/arxiv.2009.02108