On the decrease of intermittency in decaying rotating turbulence

The scaling of the longitudinal velocity structure functions, $S_q(r) = < | \delta u (r) |^q > \sim r^{\zeta_q}$, is analyzed up to order $q=8$ in a decaying rotating turbulence experiment from a large Particle Image Velocimetry (PIV) dataset. The exponent of the second-order structure function, $\zeta_2$, increases throughout the self-similar decay regime, up to the Ekman time scale. The normalized higher-order exponents, $\zeta_q / \zeta_2$, are close to those of the intermittent non-rotating case at small times, but show a marked departure at larger times, on a time scale $\Omega^{-1}$ ($\Omega$ is the rotation rate), although a strictly non-intermittent linear law $\zeta_q / \zeta_2 = q/2$ is not reached.Comment: 5 pages, 5 figures. In revision for Phys. Fluids Letter

Experimental and numerical study of mean zonal flows generated by librations of a rotating spherical cavity

International audienceWe study both experimentally and numerically the steady zonal flow generated by longitudinal librations of a spherical rotating container. This study follows the recent weakly nonlinear analysis of Busse (2010), developed in the limit of small libration frequency - rotation rate ratio, and large libration frequency - spin-up time product. Using PIV measurements as well as results from axisymmetric numerical simulations, we confirm quantitatively the main features of Busse's analytical solution: the zonal flow takes the form of a retrograde solid body rotation in the fluid interior, which does not depend on the libration frequency nor on the Ekman number, and which varies as the square of the amplitude of excitation. We also report the presence of an unpredicted prograde flow at the equator near the outer wall

Campagne CORAIL 1 de chalutage exploratoire aux îles Chesterfield et à Lansdowne ("N.O. ALIS" - 15 août au 4 septembre 1988)

Au cours de la campagne de chalutage exploratoire CORAIL 1 le N.O. ALIS a réalisé 55 traits de chalut aux îles Chesterfield, Bellona et sur le banc de Lansdowne. La proportion de fonds chalutables n'excède pas 30 % des fonds de plus de 50 m et est nulle entre 0 et 50 m. Au total 123 espèces ont été collectées dont trois pourraient être nouvelles. Les affinités des peuplements ichthyologiques rencontrés sont plus importantes avec la Nouvelle-Calédonie qu'avec l'Australie. Les densités (8 à 35 poissons/ha) et les biomasses (0.4 à 2.6 kg/ha) estimées sont très faibles, de 8 à 60 fois moindres que ce qui a été observé en Nouvelle Calédonie. Les fréquences de longueur des principales espèces sont du même ordre que celles observées en Nouvelle-Calédonie à des époques similaires. La taille maximale des espèces commerciales est supérieure à celles notées en Nouvelle-Calédonie. (Résumé d'auteur

From granular collapses to shallow water waves: A predictive model for tsunami generation

In this article, we present a predictive model for the amplitude of impulse waves generated by the collapse of a granular column into a water layer. The model, which combines the spreading dynamics of the grains and the wave hydrodynamics in shallow water, is successfully compared to a large dataset of laboratory experiments, and captures the influence of the initial parameters while giving an accurate prediction. Furthermore, the role played on the wave generation by two key dimensionless numbers, i.e., the global Froude number and the relative volume of the immersed deposit, is rationalized. These results provide a simplified, yet comprehensive, physical description of the generation of tsunami waves engendered by large-scale subaerial landslides, rockfalls, or cliff collapses in a shallow water