Investigation of flow and scour around head of a vertical wall breakwater

Karakaş, Kadir
In this study, wave induced hydrodynamic and morphodynamic processes around the head of a vertical wall breakwater are investigated by numerical and physical modeling. An open source computational fluid dynamics code was used to investigate the flow around the head of structure. The code solves incompressible Reynolds-Averaged Navier-Stokes equations with a k-omega turbulence closure. For investigating flow and scour around the structure, small-scale physical model tests were carried out in the random wave flume of Middle East Technical University, Department of Civil Engineering, Coastal and Ocean Engineering Laboratory. The experiments are composed of two stages where in the first stage the flow around the structure on a fixed bed is investigated by means of flow visualization techniques, and Acoustic Doppler Velocimeter measurements and in the second stage the scour around the structure mounted on a movable sandy bed under the same wave conditions is observed. The experiments are carried out for various Keulegan-Carpenter numbers and wave steepnesses. The wave induced scour depths are observed via underwater camcorders, and bed evolution is analyzed via semi-automatic laser scanner. When the results of scour experiments performed under regular and random waves are examined; in the dimensionless time scale, regular waves reached 25 times faster to the equilibrium state than random waves. When the KC number is around 5.5, the scour depths formed under random waves are 7 times the scour depths formed under regular waves. In the experiments, waves with different steepnesses but similar KC numbers are examined, and no significant difference was observed in the scour depths of these waves. When the shape effect of the breakwater head under random waves is examined, it is concluded that the scour depths in the tests with sharp-edged head structure are higher than the models with round head shape by 20% to 25%. Numerical model results and physical model results are found to be in agreement for the lee-wake vortex dimensions and velocity distribution measurements. In both numerical and physical model results, when the velocity distribution measurements are examined, it is observed that the velocities converge to the undisturbed velocities beyond 10B distance from the tip of the breakwater head and there is no blockage effect after this distance. It is observed that, contrary to regular and random waves, the equilibrium scour depths of solitary waves occur at the leeward of the structure, not in front of the breakwater head. Furthermore, while solitary waves have the same wave height but occur at different depths are examined, scour depth increases with increasing water depth.