The proposed contribution is dedicated to numerical methods for solving strongly coupled fluid–structure dynamic problems where the complexity of the structures and the reduced remaining fluid volume do not allow to handle their exact geometry. Porous approaches are preferred instead but it is mandatory to go beyond classical techniques to account for inertial and convective components of the flow, as explicitly required by the application of the methods to the dynamics of a set of pressurized water reactors fuel assemblies under axial flow and seismic‐like loading. A new computational framework is thus introduced with special care given to stability, robustness, and computational efficiency of the coupled solver. Comparisons with well‐chosen experimental results provide some valuable validation of the numerical methods and demonstrate the ability of the model to reproduce the hydraulic coupling between several fuel assemblies.

The vibration of rods is of prime importance to estimate their wearing due to the frictions with grids' elements. To predict this wearing, the forces exerted on the rods need to be identified and quantified. Pressure fluctuations are explored using an instrumented rod centred within a 5x5 rods bundle. Two configurations of spacer-grids are used: with and without mixing vanes respectively noted WMV and NMV. The position of the measurement point is rotated over 360° and its distance from the grids is varied from 0.5Dh to 20Dh. The results show the non-homogeneity of the azimuthal distribution of the pressure fluctuations in the near wake of the spacer-grids for both configurations. The return to a homogeneous azimuthal distribution of the pressure fluctuations is faster without mixing vanes than with mixing vanes. The intensities of the pressure fluctuations are (in average) higher for WMV than for NMV: higher by 13% and 136% respectively at distances 0.5Dh and 20Dh from the grids. Power law approximations show decreases of 〈 〉 like (⁄). and (⁄). respectively for the configurations WMV and NMV. The profiles of mean velocity and velocity fluctuations are explored around the instrumented rod using LDV. Results show oscillation of the profiles and a damping with the distance from the grids. Power law approximations show decreases of 〈 〉 ⁄ like (⁄). and (⁄). respectively for WMV and NMV. Between 2Dh and 15Dh, the dimensionless ratio of "pressure fluctuations to velocity fluctuations" 〈 〉 〈 〉 is found to increase by 70% and 100% respectively for the configurations NMV and WMV. This increase demonstrated by the combination of pressure and velocity measurements further reveals the complexity of the turbulent flow in the wake of spacer-grids.

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