Analyse mathématique et numérique d'écoulements de fluides à seuil

Arthur Marly 1, 2
2 NUMED - Numerical Medicine
UMPA-ENSL - Unité de Mathématiques Pures et Appliquées, Inria Grenoble - Rhône-Alpes
Abstract : This thesis is devoted to the flow of yield stress (or viscoplastic) fluids in pipes.Analytical and numerical difficulties lie in the multivaluation of the stress tensor in the plastic regions and in the non-differentiability of the associated minimization problem. This manuscript is organized following two main axes.First, very accurate numerical simulations were carried out using duality methods and parallel multifrontal solvers. Thus, experimental observations were recovered, namely the existence of a slip line for the flow over an obstacle and the Poiseuille-like behaviour of the velocity above this line. Moreover, the viscoplastic boundary layer theory defined by Oldroyd (1947 at high Bingham numbers) was revisited at moderate Bingham numbers in confined areas. This study provided an opportunity to go back and forth between these simulations and the physical measures of Luu et al. from IRSTEA and to perform a theoretical derivation. The boundary layer approximation is valid up to a certain extent in the cavity. An adaptation of the viscoplastic boundary layer definition is then given and allows to generalize the scalings shown by Oldroyd (1947) and Balmforth et al. (JFM 2017). These scalings are also generalized to the Herschel-Bulkley case. Then, an asymptotic analysis of the velocity and stress fields for thin layer (ε) flows is presented. A velocity development up to ε2 lets us find a Reynolds equation of same accuracy. This Reynolds equation extends the already existing results, on the one hand in the newtonian case and on the second hand for free surface flows.
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Arthur Marly. Analyse mathématique et numérique d'écoulements de fluides à seuil. Equations aux dérivées partielles [math.AP]. Université de Lyon, 2018. Français. ⟨NNT : 2018LYSEN034⟩. ⟨tel-02145210⟩

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