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This work aims to improve understanding of the damping induced by an axial flow on a rigid cylinder undergoing small lateral oscillations within the framework of the quasistatic assumption. The study focuses on the normal force exerted on the cylinder for a Reynolds number of Re = 24 000 (based on the cylinder diameter and axial flow velocity). Both dynamic and static approaches are investigated. With the static approach, fluid forces, pressure distributions and velocity fields are measured for different yaw angles and cylinder lengths in a wind tunnel. It is found that for yaw angles smaller than 5• , the normal force varies linearly with the angle and is fully dominated by its lift component. The lift originates from the high pressure coefficient at the front of the cylinder, which is found to depend linearly on the angle, and from a base pressure coefficient that remains close to zero independent of the yaw angle. At the base, a flow deficit and two counter-rotating vortices are observed. A numerical simulation using a k-ω shear stress transport turbulence model confirms the static experimental results. A dynamic experiment conducted in a water tunnel brings out damping-rate values during free oscillations of the cylinder. As expected from the linear dependence of the normal force on the yaw angle observed with the static approach, the damping rate increases linearly with the axial flow velocity. Satisfactory agreement is found between the two approaches.

Turbulent-induced vibrations of fuel assemblies in PWR power plants is a potential cause of deformation and of fretting wear damage. Because of the complexity of a 17 × 17 rod assembly with a length exceeding four meters, the prediction of its vibrations is still a challenging task as regards computer simulation. The Large Eddy Simulation (LES) technique provides the instantaneous pressure and velocity fields inside the fluid as well as the shear stress and the pressure along the walls. EDF inhouse open source CFD tool Code_Saturne is used in the present work with a 8 million cells grid to compute the flow along four sub-channels all around one fuel rod by taking into account only one mixing grid. The computations are carried out on 1024 processors of a BlueGene/L supercomputer. Hence, the overall turbulent excitation upon one single rod is estimated numerically, taking into account the specific influence of the deflectors. As regards the structure, using the forces provided by the CFD computation, a linear model of the rod based on Euler beam theory and simplified boundary conditions is proposed. The first natural modes of the structure are hence obtained, and the modal forces are estimated using the standard techniques of modal projection and joint acceptance. Estimations of the vibration amplitude of rod induced by the local flow are finally obtained, using simplified expressions of the added mass and of the damping coefficient. The amplitudes are significant for the first mode essentially, and reach a value of the order of the μm, with a maximum around 6 μm.