Lagrangian Characteristics of Surface Turbulence

While tracing small particles floating at the surface of a steady, uniform, open channel flow, measurements were obtained of the Lagrangian characteristics of surface turbulence. The experimental technique was photographical using a stroboscope as light source. In this way the changing velocity of a particle was observed as it moves along its path line. The width to depth ratio of the flow considered was large so that dispersion was due exclusively to diffusion caused by surface turbulence. Mean square values, time scales, covariance functions, and variance spectra of the Lagrangian velocity fluctuations were obtained. It was found that the estimated Lagrangian covariance functions might be very closely approximated by exponential functions.