** ****Centrifugal instability of Stokes layers in crossflow: the case of a forced cylinder wake**

J. D’Adamo, R. Godoy-Diana & J. E. Wesfreid

**Proceedings of the Royal Society A ****471**: 20150011 (2015).

DOI:10.1098/rspa.2015.0011

A circular cylinder oscillating in a viscous fluid produces an axisymmetric Stokes layer, a fundamental flow susceptible to centrifugal instabilities [see e.g. Seminara & Hall, *Proc. Roy. Soc. London A*** 350**, 299 (1976)]. In the present work we study such problem in the wake flow around a circular cylinder at Re = 100 performing rotary oscillations. For a forcing frequency ff and amplitude Ut, the non-dimensional control parameters f+ = ff /fn and A = Ut/U∞ are related to the flow properties, the inflow velocity U∞ and the natural vortex shedding frequency fn. In a previous work [D’Adamo et al., *Phys. Rev. E.* **84**, 056308 (2011)], we identified experimentally a zone in the parameter space with forcing at frequencies lower than the natural vortex shedding frequency, where the flow exhibited some turbulence features such as a continuous spectrum for the velocity components, and multiple vortex splitting interactions in the wake. We show here using numerical simulations that these observations result from a 3D centrifugal instability.

Supplementary video material from Juan D’Adamo:

Centrifugal instability in cross flow from Juan D'Adamo on Vimeo.