Experimental study of large turbulent structures in a breaking solitary wave using particle image velocimetry

This study focused on large turbulent structures under a breaking solitary wave. Stereoscopic Particle Image Velocimetry (PIV) was used to measure approximately a 17 cm by 17 cm area in the horizontal plane. PIV measurements were taken at approximately the middle of the still water column because it is supposedly the farthest away from the free surface and bottom where obliquely descending eddies are well developed. The solitary wave broke as a plunging wave and had already broken at the location of the PIV measurements. By measuring the velocity field under a solitary wave, the effects of the wave train and residual turbulence do not affect the results.; The results presented focused on large turbulent structures. Two different types of turbulent structures were observed, spiral vortices and a downburst. Vortices were seen in nearly every trial where four different types of vortices were viewed. The downburst was observed in all trials. Fixed-point measurements were extracted from the PIV velocity fields for selected test runs. From these point measurements, Reynolds stress and turbulent kinetic energy time series were plotted. Spikes or peaks were related to individual eddies or other flow structures. Obliquely descending eddies (ODE) are a pair of counter-rotating vortices. ODE were observed under a breaking wave in consecutive velocity fields in approximately one-third of the test runs.; Overall, this research project has provided new information on the velocities and turbulent structures under a breaking wave in a laboratory surf zone. Large-scale turbulent structures were analyzed in this experiment. This particular study identified the different types of turbulent structures and obliquely descending eddies. More research is needed to determine the evolution of large eddies and to better understand the kinematics and dynamics of turbulent structures under breaking waves.