Three-dimensional measurements of scalar dispersion in grid turbulence

The three-dimensional scalar-dispersion field of a passive Lagrangian-marker contaminant released in grid-generated turbulent flow with an initial Taylor Reynolds number of $\sim 40$, was investigated. The experiments were conducted in the GALCIT Free Surface Water Tunnel using laser-induced fluorescence, a two-dimensional galvanometric optical scanner, and recorded with a fast-framing CCD camera and data acquisition system that sustained $10^8\,$pix/s, at $12\,$bits/pix. The resulting data frames were processed to compensate for temporal and spatial skewing, and resampled on a Cartesian grid for subsequent processing. The spatial structure of the scalar field downstream of the grid will be presented and discussed.