Jeudi 27 novembre à 14h00 ; salle des séminaires IRPHE
Abstract: Experiments have revealed that, starting from a linear with height density profile, forced stably-stratified flows can produce a step-like vertical density profile, where layers, with well-mixed almost constant density, alternate with interfaces where large vertical gradients are concentrated.
Here we report a numerical study at moderate resolution but with unprecedented time extension (up to fO(10^4) turnover times) of forced Boussinesq flows for three different stratification strengths, quantified in terms of the Froude number, Fr=0.1, 0.3 and Fr=0.6. The staircase profile, found for the two smallest values, coarsens either by decay of interfaces or by merging of these. The kinetic energy remains roughly stationary during decays, whereas abrupt and strong excursions are observed when pairs of interfaces merge.
Intermittency of both vertical velocity and density fluctuation is observed only in proximity of the layer-interface borders.
Acknowledgements: *This work is done in collaboration with Niccolo' Cocciaglia, Fabio Bonaccorso and Luca Biferale.
Alessandra Lanotte, Istituto di Nanotecnologia, Consiglio Nazionale delle Ricerche