Evaluation of transient turbulent flow fields using digital cinematographic particle image velocimetry

This paper describes an experimental development for temporal and spatial r econstruction of continuously varying flow fields by means of digital cinem atographic particle image velocimetry (PIV). The system uses a copper-vapor laser illumination synchronized with a high-speed camera, and continuously samples at 250 fps to measure transient and non-periodic turbulent flows w ith relatively low frequencies, i.e., the surf zone turbulence produced by depth-limited wave break in a long laboratory flume. The use of the develop ed PIV system comprehensively records the temporal development of both phas e-averaged and instantaneous turbulent vortex flows descended from the brea king waves to the bottom. Also, the measured power spectra show harmonic fr equencies, ranging from the orbital frequency of 0.5 Hz up to the order of 5 Hz, and the well-known -5/3 dependence upon the turbulence fluctuation fr equencies thereafter.