A 3D investigation of the dynamic loads over an array of in-line cylinders at low KC and Re numbers

Abstract

The oscillating flow around an infinite array of circular cylinders at low Keulegan-Carpenter numbers and Reynolds numbers is investigated numerically 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 second and the third are asymmetric and 3D. In each regime, the gap between two neighboring cylinders has been varied in a very wide range, from the case of practically isolated cylinder to the case of very strong interference. As regards the isolated cylinder, the mean value of the inertia coefficient is much more affected by 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 isolated cylinder are known.