Turbulent Flow Induced by Regular and Irregular Waves above a Steep Rock-Armored Slope

Abstract

The turbulent flow induced by regular and irregular waves on a steep rock-armored slope of 1:3 was studied experimentally. The armor layer consisted of two rows of stones with a median weight of 0.925 N. Four cases of incident waves, whose heights satisfied the hydraulic stability criterion for the armor layer, were tested. The measured wave reflection coefficients were in accordance to values in the literature. Flow measurements were performed using an underwater particle image velocimetry (PIV) system to record instantaneous velocity fields in the region seaward of the breaking point on the slope. In all cases, a return current toward deep water developed, and its magnitude was stronger for the regular than the irregular waves. The vertical profile of the current was approximately linear, and it compared well with a semianalytical model in the literature, which was modified for the present application. The generation of turbulence was enhanced mainly by flow separation resulting from the rough geometry of the armor layer and secondarily by local outflow/inflow resulting from the porosity of the armor layer, and it was correlated to ejection and sweep events. For the regular waves, the relative contributions of the streamwise, transverse, and vertical velocity fluctuations to the mean turbulent kinetic energy were 0.44, 0.28, and 0.28, respectively. The behavior of the phase-averaged velocity field for the regular waves demonstrated that the armor layer behaved as a rough impermeable surface rather than a true porous medium because of the small number (two) of rows of stones.