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Article Dans Une Revue Journal of Fluid Mechanics Année : 2023

Internal shear layers in librating spherical shells: the case of attractors

Jiyang He
Benjamin Favier
Michel Rieutord

Résumé

Following our previous work on periodic ray paths (He et al. 2022), we study asymptotically and numerically the structure of internal shear layers for very small Ekman numbers in a threedimensional (3D) spherical shell and in a two-dimensional (2D) cylindrical annulus when the rays converge towards an attractor. We first show that the asymptotic solution obtained by propagating the self-similar solution generated at the critical latitude on the librating inner core describes the main features of the numerical solution. The internal shear layer structure and the scaling for its width and velocity amplitude in 1/3 and 1/12 respectively are recovered. The amplitude of the asymptotic solution is shown to decrease to 1/6 when it reaches the attractor, as is also observed numerically. However, some discrepancies are observed close to the particular attractors along which the phase of the wave beam remains constant. Another asymptotic solution close to those attractors is then constructed using the model of Ogilvie (2005). The solution obtained for the velocity has an (1/6) amplitude, but a different self-similar structure than the critical-latitude solution. It also depends on the Ekman pumping at the contact points of the attractor with the boundaries. We demonstrate that it reproduces correctly the numerical solution. Surprisingly, the numerical solution close to an attractor with phase shift (that is an attractor touching the axis in 3D or in 2D with a symmetric forcing) is also found to be (1/6) but its amplitude is much weaker. However, its asymptotic structure remains a mystery.
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Dates et versions

hal-04286209 , version 1 (15-11-2023)

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Jiyang He, Benjamin Favier, Michel Rieutord, Stéphane Le Dizès. Internal shear layers in librating spherical shells: the case of attractors. Journal of Fluid Mechanics, 2023, 974, ⟨10.1017/jfm.2023.761⟩. ⟨hal-04286209⟩
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