Séminaire de Jean-Baptiste Gorce (Lab. Matière et Systèmes Complexes, Univ. Paris)Séminaire
Turbulence generated by magnetic stirrers
Jean-Baptiste Gorce, Laboratoire Matière et Systèmes Complexes, Université de Paris
Turbulent flows develop in different situations: atmospheric winds, ocean currents, or industry. Although there is a large diversity of turbulent flows, they all show some similarities and require a comprehensive understanding. Here, we present a technique for generating turbulent flows using magnetic stirrers immersed in a fluid. A vertical oscillating magnetic field transfers kinetic energy to the magnetic stirrers by imposing an angular momentum. The kinetic energy of the magnetic stirrers is then transferred to the surrounding fluid randomly in both space and time. The generated flow is statistically homogeneous, stationary, isotropic, and satisfies the assumptions of the Kolmogorov theory. Velocity field measurements show that the kinetic energy injected into the fluid is dissipated at small scales by a self-similar turbulent cascade mechanism. The flow at large scales exhibits different dynamics. The energy modes are in equipartition, and the energy flux is zero on average in the large scale interval. These observations suggest a statistical equilibrium regime at large scales and thus the use of statistical mechanic concepts to describe turbulent flows.
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