Statistics and dynamics of the boundary layer reattachments during the drag crisis transitions of a circular cylinder
Résumé
Time series of pressure measured on the periphery of the central section of a
circular cylinder of aspect ratio 22 are used to investigate the dynamics of the
local reattachments during the drag crisis transitions. A succession of multi-stable
dynamics are identified and characterized through conditional statistical analysis as
the Reynolds number is increased. The first transition marking an abrupt weakening
of the periodic pressure fluctuations associated to the global shedding dynamics is
accompanied by the appearance of symmetric and bistable perturbations. Afterwards,
two scenarii of asymmetric and symmetric boundary layer reattachments are found.
The asymmetric scenario leads to two transitions. During the first transition, the
flow explores randomly three stable states to eventually stabilize on the state corresponding
to the permanent reattachment on one side of the cylinder. The second
transition is bistable and leads to the permanent reattachment on both sides. For the
second symmetric scenario, the boundary layer reattachments occur simultaneously
on both side of the cylinder. In that case, the flow explores randomly two stable
states to eventually stabilize on the state of full reattachment. Pressure distributions
of all of these states are characterized as well as their corresponding probabilities
during the drag crisis transitions of the critical regime.
Domaines
Sciences de l'ingénieur [physics]
Origine : Fichiers produits par l'(les) auteur(s)
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