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Écoulement et entraînement d’air autour d’un cylindre vertical partiellement immergé

Abstract : The flow past ships or an emerged body such as bridge pilar, is a fundamental, familiar and fascinating sight.Measurements and modelling of this simple flow can have relevance to offshore structures and renewable energy systems. The interaction of such structures with marine environment lead to drag, lift forces and free-surface effects.Our current problem is simplified by considering cylindrical geometry. This work presents experimental results, in which vertical cylinders are translated at constant speed through water initially at rest, and numerical results using YALES2 computing code based on finite volume method. The cylinders are partially immersed, then the motion induces turbulent wake and free-surface deformation. The flow is governed by the Reynolds and Froude numbers defined with cylinder diameter. The explored range of parameters are in the regime of turbulent wake with experiments carried out for Reynolds number up to 240 000, and Froude number up to 2.4. The focus here is on drag force measurements and strong free-surface deformation up to rupture and air-entrainment. Two modes of air-entraiment have been observed: (i) in the wake of the cylinder and (ii) in a cavity along the cylinder wall. Results are as follows. First, a scaling for the critical velocity for air-entrainment in the cavity proportional to D1/5 proposed by Benusiglio is recovered. Secondly, drag coefficients measured by piezoelectric sensors are smaller in two phase flow compared to monophasic case, and air-entrainment in the cavity enhances this decrease. Numerically, YALES2 uses level-set method for the descirption of the free-surface, and is able to reproduce air-entrainment phenomenon, free-surface deformations and flow dynamics around the cylinder. The present work expands the range of dimensionless parameters and highlights free-surface effects on drag forces.
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  • HAL Id : tel-02585789, version 1

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Valentin Ageorges. Écoulement et entraînement d’air autour d’un cylindre vertical partiellement immergé. Mécanique des fluides [physics.class-ph]. Normandie Université, 2019. Français. ⟨NNT : 2019NORMLH23⟩. ⟨tel-02585789⟩

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