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Les ferrofluides : ondes de surface, résistance de vague et simulation de la convection dans le manteau terrestre

Abstract : Ferrofluids are stable colloidal solutions of nanoparticles. The influence of a magnetic can generate several hydrodynamic instabilities, either at the interfaces or in the bulk. After a short introduction to ferrofluids, three situations are examined. Surface waves are susceptible to be amplified by a normal magnetic field, leading to the Rosensweig instability. An experiment is designed in order to measure the dispersion relation that is otherwise obtained by linear analysis. The shadowgraph method that is used allows to observe a pre-transitional deformation, as well as azimutal wavelets close to the magnetic field threshold. The wave resistance is the force that puts up against the movement of an object at the surface of a fluid, caused by the emission of surface waves. If its size is much smaller that the capillary length, the wave resistance is to be zero below a critical speed, the minimum velocity of capillary-gravity waves. Beyond, it is an increasing function of the movement speed. An experiment has been designed in order to observe those recent theoretical predictions stemming from linear analysis. Fluids with different viscosities have been employed. With ferrofluids, we show that it is possible to reduce at will the critical velocity. In any case, the critical phenomenon is observed in accordance with the theory. However, the wave resistance seems to be a non-monotonic function of speed. Lastly, the original properties of ferrofluids allow conceiving a magneto-caloric experiment in central geometry, similar to the Rayleigh-Bénard convection. By the use of appropriate scaling laws, a laboratory model is elaborated that simulates the earth mantle convection: the Rayleigh number is in the order of a million. The temperature field is observed by infrared imaging. Moving convection cells are observed, and the Nusselt number is obtained as a function of the Rayleigh number.
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Contributor : Julien Browaeys <>
Submitted on : Wednesday, October 27, 2004 - 6:13:00 PM
Last modification on : Tuesday, April 13, 2021 - 7:16:01 PM
Long-term archiving on: : Friday, April 2, 2010 - 9:10:36 PM


  • HAL Id : tel-00007235, version 1



Julien Browaeys. Les ferrofluides : ondes de surface, résistance de vague et simulation de la convection dans le manteau terrestre. Dynamique des Fluides [physics.flu-dyn]. Université Paris-Diderot - Paris VII, 2000. Français. ⟨tel-00007235⟩



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