Laboratory Measurements of Void Fraction and Turbulence in the Bore Region of Surf Zone Waves

Abstract

Laboratory measurements of the instantaneous free surface, horizontal velocity, and void fraction fluctuations were made simultaneously for three cases of regular waves breaking on a plane slope. The data were reduced by ensemble averaging to quantify the temporal variation of the turbulence intensity and void fraction above trough level in the aeration region of the breaking waves. The cross-shore location of the measurements was restricted to the transition region marked by a rapid decrease in wave height. The study showed that the maximum ensemble-averaged void fractions were between 15 and 20% and that the temporal variation of the normalized void fraction above the still water level could be modeled by linear growth followed by exponential decay. The temporal variation of void fraction above the still water normalized by the wave period and average void fraction appears to be self-similar.