Two-dimensional experimental and numerical investigations of perforated plates in oscillating flow, orbital flow and incident waves

Abstract

The hydrodynamic loads on two-dimensional perforated plates are investigated experimentally and numerically. Two single perforated plate configurations, consisting of rows of either circular or square cylinders, are studied. Experiments and simulations are performed for oscillating flow, orbital flow and waves. The Keulegan–Carpenter (KC) number and period of oscillation are varied. The hydrodynamic forces and coefficients are highly KC number dependent. There is in general small dependence on the period of oscillation. An exception is in wave tests where the normalized force on the structures depend on both the wave length-to-plate diameter ratios and the submergence. Added mass and damping coefficients are presented for oscillating and orbital flow conditions. The hydrodynamic force on both configurations is dominated by damping. We find in general good agreement between the experimental and numerical results.We highlight some aspects of the influence from plate-end flow separation on the forces of the plates. A considerable reduction in the hydrodynamic forces is found in orbital motion compared to oscillating flow, increasingly so as the KC number is increased. Asymmetric flow patterns, where the vortex generation at the plate-ends occurs only on one side at a time, are observed in orbital flow, whereas the plate-end vortices from the two sides of the plate are generated simultaneously in oscillating flow. Streamline plots indicate that the relative importance of vortex generation from the plate-ends increases with increasing KC number.