A 3d Investigation Of The Dynamic Loads Over An Array Of In-line Cylinders At Low Kc And Re Numbers

Résumé: The oscillating flow aroundan infinite array of circular cylinders at low Keulegan-Carpenter numbers andReynolds numbers is investigatednumerically using a 3D mathematical model. Three different regimes of the Tatsuno and Bearman (1990) map are investigated; the first one is a 2D symmetric regime, whereas the secondandthe thirdare asymmetric and3D. In each regime, the gap between two neighboring cylinders has been varied in a very wide range, from the case of practically isolatedcylinder to the case of very strong interference. As regards the isolated cylinder, the mean value of the inertia coefficient is much more affectedby the 3D effects than that of the drag coefficient. Conversely, the variation along the axial direction of the sectional drag coefficient is much stronger than that found for the sectional inertia coefficient. In all cases investigated, the reduction of the gap between cylinders has two main effects: first, it causes the reduction of the Morison coefficients; second, in the 3D regimes, the gap enhances 3D motion in the range of moderate values due to the interaction between vortex structures released by two neighboring cylinders, whereas a further reduction of the gap in the range of small values tends to reduce the three-dimensionality of flow field up to a complete suppression occurring for very small values of the gap. Finally, we propose a very simple parameterization that gives the Morison coefficients as a function of the gap once the values for the case of isolatedcylinder are known.

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