## Abstract

In this experimental note, we consider the centrifugal instability of a laminar shear layer, generated by the impulsive start of the rotation of a circular solid cylinder about its vertical axis immersed in a linearly stratified fluid. The flow is determined by the Reynolds number, Re, based on the cylinder rotation rate and the cylinder radius, and the Froude number, F_{r}, represented by the ratio of the rotation frequency Ω over the buoyancy frequency N. The onset of the instability starts when the boundary layer reaches a certain thickness. We show for this boundary layer that there is a transition from the centrifugally unstable regime to a wave-like regime at Fr ≈ 1 and a stable flow below a critical Reynolds number. We focus on the centrifugally unstable regime Fr⪆1, for which the onset time and wavelength are predicted by scaling laws that depend on the Reynolds number. Agreement with the theoretical prediction of Kim and Choi [“The onset of instability in the flow induced by an impulsively started rotating cylinder,” Chem. Eng. Sci. 60, 599-608 (2005)] in a homogeneous fluid confirms that the instability of this boundary layer is not modified by the presence of stratification. These results therefore show that the centrifugal instability of the spin-up boundary is dominated by inertial motions, suggesting that close lateral boundaries, as in thin-gap stratified Taylor-Couette flow, increase the effects of buoyancy on the instability and wavelength.

Original language | English |
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Article number | 084103 |

Number of pages | 6 |

Journal | Physics of Fluids |

Volume | 30 |

Issue number | 8 |

DOIs | |

Publication status | Published - 1 Aug 2018 |