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19 octobre 2017: 1 événement


  • Séminaires Internes

    Jeudi 19 octobre 11:00-12:00 - Benjamin Dollet

    [INTERNE] Boundary layers in fluid mechanics, and their influence on modelling in physics

    Résumé : Although the bases of fluid mechanics are well established since the beginning of the nineteenth century, the subtle role of viscosity in inertia-dominated flows has long been overlooked. The role of inertia and viscosity in flows are compared by a dimensionless quantity, the Reynolds number. If this number is large, it seemed reasonable to neglect viscosity. However, this lead to major inconsistencies, the most known being d’Alembert’s paradox, namely the incapacity of the theory to predict the drag experienced by vehicles or planes. Ludwig Prandtl (1875-1953), a German engineer and physicist, solved this problem by recognising that however high the Reynolds number be, viscosity remains essential in a thin region close to solid boundaries. This is the basis of the so-called boundary-layer theory.
    I will first briefly present these ideas, then I will put into perspective boundary layers into a more general context in physics, namely the "art" of doing approximations when a physical effect seems to be negligible : perturbation methods.

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