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Publications (5)9.67 Total impact

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    ABSTRACT: We report the observation of dynamo action in the von Kármán sodium experiment, i.e., the generation of a magnetic field by a strongly turbulent swirling flow of liquid sodium. Both mean and fluctuating parts of the field are studied. The dynamo threshold corresponds to a magnetic Reynolds number R(m) approximately 30. A mean magnetic field of the order of 40 G is observed 30% above threshold at the flow lateral boundary. The rms fluctuations are larger than the corresponding mean value for two of the components. The scaling of the mean square magnetic field is compared to a prediction previously made for high Reynolds number flows.
    Physical Review Letters 02/2007; 98(4):044502. · 7.73 Impact Factor
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    ABSTRACT: We study the magnetic induction in a confined swirling flow of liquid sodium, at integral magnetic Reynolds numbers up to 50. More precisely, we measure in situ the magnetic field induced by the flow motion in the presence of a weak external field. Because of the very small value of the magnetic Prandtl number of all liquid metals, flows with even modest R-m are strongly turbulent. Large mean induction effects are observed over a fluctuating background. As expected from the von Karman flow geometry, the induction is strongly anisotropic. The main contributions are the generation of an azimuthal induced field when the applied field is in the axial direction (an Omega effect) and the generation of axial induced field when the applied field is the transverse direction (as in a large scale alpha effect). Strong fluctuations of the induced field, due to the flow nonstationarity, occur over time scales slower than the flow forcing frequency. In the spectral domain, they display a f(-1) spectral slope. At smaller scales (and larger frequencies) the turbulent fluctuations are in agreement with a Kolmogorov modeling of passive vector dynamics.
    Physics of Fluids 01/2002; · 1.94 Impact Factor
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    ABSTRACT: We demonstrate the feasibility of studying dunes in a laboratory experiment. It is shown that an initial sand pile, under a wind flow carrying sand, flattens and gets a shape recalling barchan dunes. An evolution law is proposed for the profile and the summit of the dune. The dune dynamics is shown to be shape invariant. The invariant shape, the “dune function” is isolated. To cite this article: O. Dauchot et al., C. R. Mecanique 330 (2002) 185–191.RésuméNous montrons qu'il est possible d'étudier les dunes en laboratoire. Un tas de sable initial, soumis à un écoulement d'air chargé en sable, s'applatit et prend une forme qui rappelle celle d'une barchane. Nous proposons une loi d'évolution du profil et du sommet de la dune. Nous montrons que la dynamique de la dune est invariante de forme, et nous isolons cette forme invariante, « la fonction dune ». Pour citer cet article : O. Dauchot et al., C. R. Mecanique 330 (2002) 185–191.
    Comptes Rendus Mécanique. 01/2002; 330(3):185–191.
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    ABSTRACT: We study the magnetic induction in a confined swirling flow of liquid sodium, at integral magnetic Reynolds numbers up to 50. More precisely, we measure in situ the magnetic field induced by the flow motion in the presence of a weak external field. Because of the very small value of the magnetic Prandtl number of all liquid metals, flows with even modest Rm are strongly turbulent. Large mean induction effects are observed over a fluctuating background. As expected from the von Kármán flow geometry, the induction is strongly anisotropic. The main contributions are the generation of an azimuthal induced field when the applied field is in the axial direction ~an V effect! and the generation of axial induced field when the applied field is the transverse direction ~as in a large scale a effect!. Strong fluctuations of the induced field, due to the flow nonstationarity, occur over time scales slower than the flow forcing frequency. In the spectral domain, they display a f21 spectral slope. At smaller scales ~and larger frequencies! the turbulent fluctuations are in agreement with a Kolmogorov modeling of passive vector dynamics.
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