Extracting Numbers From Tracer Flow Visualization: High Attack-Angle Vanes

High attack-angle vanes have been proposed as a means of maintaining sediment in suspension in rivers and streams. Laboratory and computer studies have, up to now, been unable to describe how the flow mechanism actually works in the sediment-suspension mode. A turbulent-flow tracer has been used to study model vanes in a small water channel at the University of Bristol. The sediment-suspension capabilities of such vanes becomes evident from their highly swirling non-symmetric Ka´rma´n vortex-type wakes. The wake patterns have been analyzed using video recordings and frame-counting software. Using the video frame rate as a time base, Strouhal numbers and velocities in the vane wake can be extracted by following the movement of particular tracer strands.