The Structure of Turbulence and Other Motions Beneath an Air-Water Interface

Both physical experiments and numerical simulation experiments were used to study three-dimensional, unsteady, real-fluid flows beneath the alr-water interface. The focus of the numerical work was the kinematics of the interaction between surface waves and a turbulent current. The numerical method produces a time-accurate, large-eddy simulations of an unsteady turbulent free-surface flow in three space-dimensions. The simulations show that the turbulence in the near-surface region is enhanced by the interactions between non-breaking waves and a turbulent shear current. A novel measurement technique, digital particle tracking velocimetry DFTV, was developed and used to make near-surface measurements of the velocity field in wavy and non-wavy open channel flows. This approach is based on cross-correlation digital particle image velocimetry DPIV and results in significantly improved resolution and accuracy. In particular, this approach allows for the direct measurement of mean squared fluctuating gradients, and thus several important components of the turbulent dissipation.