Projet ANR-07-BLAN-0182 – IMAGINE : Instabilités Magnéto-Inertielles
Programme : Blanc (BLANC) 2007
Année de financement : 2007
Coordinateur du projet : CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE PROVENCE CORSE (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE PROVENCE CORSE)
Partenaires : Centre national de la recherche scientifique; Université Pierre et Marie Curie
Montant : 140000.0 euros
Date de début : 2007
Durée : 24 mois
Résumé : "Inertial instabilities are found in industrial applications, related in particular to aeronautics (elliptic instabilities of the vortices of airplanes, precessional instabilities of the rotating fluid tanks of rockets...). However, such inertial instabilities can also be present in many natural systems such as stratified atmospheres or oceans or in the liquid cores of certain planets and satellites [Kerswell and Malkus, 1998] (Earth, Io, Ganymède...), where they could influence or even control the processes of generation of a magnetic field. The recent success of three different dynamo experiments (Riga [Gailitis A et al., Phys. Rev. Lett. 84 (2001) 4365], Karslruhe [R. Stieglitz and U. Müller, Phys. Fluids 13, 561 (2001)] and Cadarache [Monchaux et al., Phys. Rev. Lett. 98 (2007) 044502]) showed that if the power injected in a liquid metal flow is sufficient but also if the geometry of these flows are correctly choosen, a natural growth of a magnetic field is possible as expected by the theory. However, the exact mechanism of the generation of a magnetic field in particular in planetary cores is still an open question. This problem is the subject of an intense international competition with numerical computations that simulate convection driven geodynamos [J. Aubert, J .Fluid Mech. (2005), 542: 53-67] or precessionnal geodynamos [A. Tilgner, Phys. Fluids 17 (2005), 034104] and experiments on MHD geophysical flows [H. C. Nataf et al., Geophys. Astrophys. Fluid Dyn. 100,281 (2006)]. The generally accepted idea of a convection driven dynamo for Earth relies on the existence of a solid inner core whose crystallization provides the energy for the fluid motions. This scenario presents however several drawbacks such as the origin of the energy in the early Earth whereas the solid inner core did not yet exist. Our objectives focus on the possible fluid motions that may appear in planetary cores because of different types of forcing. In particular, our principal objectives will be to quantify the characteristics of inertial instabilities of rotating fluid flows in configurations where they are coupled to other phenomena which can be met (but not only) in geophysical configurations. In addition to the purely geometrical aspects (presence of a solid inner core, flatness at the poles...), we wish to study their interactions with other mechanisms whose importance in the planetary cores was already stressed, in particular the presence of a magnetic field and/or convective motions. The present project corresponds to a natural interdisciplinary evolution of the initial scientific programs of the demanding research group. It received already the support of CNRS by the recruitment of a young geophysicist (M. Le Bars) and lead to the creation of a new team at IRPHE entitled ""Rotating flows and Geophysics. It will be reinforced by the visit of A. Tilgner from the Geophysical laboratory of Göttingen (non permanent CNRS position obtained for 2007) and by a collaboration with J. Aubert from the Institut de Physique du Globe (Paris). The proposal is thus based on a good balance and a strong complementarity between experimentalists and theoreticians on one hand, hydrodynamicians and geophysicists on the other hand. Moreover the team would be supplemented by the recruitment of a post-doctorant specialized in the numerical simulations of instabilities of rotating flows. This will permit to implement in the team an expertise in numerical simulation of this type of flows. Let us note moreover that the interdisciplinary character of our program will be still reinforced by a collaboration with researchers from the LI2C whose expertise in liquid metal and ferrofluids chemistry will be necessary in order to develop the Magneto-Hydrodynamic part of the project. The principal objective of the present project is to quantify in a systematic way the characteristics of inertial instabilities of rotating flows in configurations close to natural configurations...