Analysis of an ensemble of plunging breaking events

The dynamics of three plunging breaking waves is studied through measurements of the evolution of their free surface profiles during 10 repeated breaking events for each wave. The waves are created from dispersively focused wave packets which are generated by a highly accurate programmable wave maker. The wave maker motions that create the three breakers are identical except for the overall amplitude. Breaker profiles are measured with a cinematic laser induced fluorescence technique covering a streamwise region of approximately one wavelength. The 10 repeated sets of breaker profiles are spatially aligned at the time of jet impact. The aligned data is used to create spatio-temporal maps of the ensemble average surface height and the standard deviation of both the local normal distance from the instantaneous mean profile and the local arc length relative to the local mean arc length of the instantaneous mean profile. It is found that the mean and standard deviation maps contain strongly correlated localized features that indicate that the transition from laminar to turbulent flow is a highly repeatable process. Regions of high standard deviation include the splash created by the plunging jet impact as well as the site where the air pocket entrained under the plunging jet comes to the surface and pops on the back face of the wave.