Focused waves on shear currents interacting with a vertical cylinder

Abstract

This paper reports on numerical simulations of focused waves on currents interacting with a vertical cylinder. The simulations are conducted using a Numerical Wave Tank (NWT) based on the method of Large Eddy Simulations (LES). Experimental data are utilised to validate the NWT’s ability to reproduce accurately the wave–current kinematics for a following, an opposing and no current case, all under the same wave condition. The LES-predicted results in terms of wave elevations and velocities under wave crest and trough agree well with the experimental data for all conditions. The instantaneous and mean velocity field at various locations and current conditions as well as three-dimensional visualisations using isosurfaces of the Q-criterion showcase the complexity of the wave–current-cylinder interactions which is manifested in turbulence structures near the cylinder in the form of the horseshoe vortex, flow separation vortices as well as shear layer vortices in the cylinder wake. The effect of the focused wave on the distribution of the wall shear stress in the vicinity of the cylinder is quantified: while the overall distribution of the wall shear stress is similar with and without waves, the wall shear stress attains substantially higher values locally, up to 80 times, when the focused wave passes by than in the shear current only scenario.