Centrifugal instability of Stokes layers in crossflow: the case of a forced cylinder wake
arXiv:1504.06229 · doi:10.1098/rspa.2015.0011
Abstract
The wake flow around a circular cylinder at performing rotatory oscillations has been thoroughly discussed in the literature, mostly focusing on the modifications to the natural Bénard-von Kármán vortex street that result from the forced shedding modes locked to the rotatory oscillation frequency. The usual experimental and theoretical frameworks at these Reynolds numbers are quasi-two-dimensional, since the secondary instabilities bringing a three-dimensional structure to the cylinder wake flow occur only at higher Reynolds numbers. In the present paper we show that a three-dimensional structure can appear below the usual three-dimensionalization threshold, when forcing with frequencies lower than the natural vortex shedding frequency, at high amplitudes, as a result of a previously unreported mechanism: a pulsed centrifugal instability of the oscillating Stokes layer at the wall of the cylinder. The present numerical investigation lets us in this way propose a physical explanation for the turbulence-like features reported in the recent experimental study of D'Adamo et al. (2011).
arXiv comment18 pages, 13 figures. To appear in Proc. Roy. Soc. A. For supplementary video material, see http://vimeo.com/123152022