Caractérisation des forces fluides s'exerçant sur un faisceau de cylindres oscillant latéralement en écoulement axial

Abstract : This thesis presents an experimental and a numerical study of the fluid forces exerted on a cylinder or a cylinder array oscillating laterally in an axial flow. The parameters of the system are the amplitude, the oscillation frequency, the confinement and the length to diameter ratio of the cylinder. The objective is to determine the fluid damping created by the axial flow, i.e. the dissipative force. The industrial application of this thesis is the determination of the fluid damping of the fuel assemblies in the core of a nuclear power plant during an earthquake. The study focuses on the configurations where the oscillation velocity is small compared to the axial flow velocity. In a first part, we study the case of a cylinder with no confinement oscillating in axial flow. Two methods are used: a dynamical and a quasi-static approach. In dynamics, the damping rate is measured during free oscillations of the cylinder. In the quasi-static approach, the damping coefficient is calculated from the normal force measured on a yawed cylinder. The range of the small ratios between the oscillation and the axial flow velocities corresponds to a range of low yaw angle where the cylinder is in near-axial flow in statics. The case of a yawed cylinder has been studied both experimentally with experiments in a wind tunnel and numerically with CFD calculations. The analyses of the fluid forces shows that for yaw angles smaller than 5°, a linear lift with the yaw angle creates the damping. The origin of the lift force is discussed from pressure and velocity measurements. The results of the quasi-static approach are compared to the results of the dynamical experiments. In a second part, an experimental study is performed on a rigid cylinder array made up of 40 cylinders oscillating in an axial flow. The normal force and the displacement of the cylinder array are measured simultaneously. The added mass and damping coefficient are calculated and their variation with the amplitude, the oscillation frequency and the axial velocity are studied. The force measurements show that the damping coefficient only depends on a single parameter: le ratio between the amplitude of the oscillation velocity and the axial flow velocity.
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Contributor : Lise Divaret <>
Submitted on : Thursday, July 10, 2014 - 4:04:03 PM
Last modification on : Wednesday, July 3, 2019 - 10:48:04 AM
Long-term archiving on : Friday, October 10, 2014 - 12:21:08 PM

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Lise Divaret. Caractérisation des forces fluides s'exerçant sur un faisceau de cylindres oscillant latéralement en écoulement axial. Mécanique des fluides [physics.class-ph]. ENSTA ParisTech, 2014. Français. ⟨NNT : 447⟩. ⟨pastel-01022672⟩

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