Macroturbulent velocity measurement in wave breaking

MOSSO C; A RODRIGUEZ; JP SIERRA; SANCHEZ ARCILLA A

Turbulent Diffusion in the Environment

ERCOFTAC ISBN: 84-85433-9

Lugar: Barcelona; Año: 2000; p. 155 - 163

Studies of turbulence have been done in almost every field of fluid mechanics. However, the study of turbulence in the surf zone is a very complex task due to the overlapping of spatial and temporal scales of the macrovortices and the oscillatory flow associated to wave motion, and the difficulty of measuring in adverse field conditions.The study area where the experiments were carried out to obtain hydrodynamic data is the Trabucador Bar surf-zone of the Ebro Delta, located on the Spanish Mediterranean coast, (see figure 1).The methodology developed to analyze macroturbulence, splitting the turbulent fluctuations (high frequency) and the oscillatory flow (wave motion) from the total signal appears to work successfully, although care should be taken due to the non-negligible dependence of the results on the filtering technique.The hybrid method used to define the cut-off frequency for macroturbulence, seems to work well inside the surf-zone. Computations show a non homogeneous vertical structure for turbulence, being higher near the surface probably due to the entrainment of wave-induced turbulence. The local equilibrium assumption for surf-zone turbulence seems to be confirmed, since the turbulent dissipation  is only important in the upper third of the water column, showing that the energy is mainly dissipated where it is produced.