Michael Böhmer, Heiko Hinrichs, Klaus D. Hinsch, Jan Kick stein, René Netter, Christof Surmann, Dept. of Physics, Oldenburg Univ., Oldenburg, Germany.
Much information about the spatial and temporal structure of fluid flows is gained by optical investigation of the distribution or motion of foreign matter introduced into the flow. Flow visualization, for example, relies on the propagation of smoke clouds or dye tracks. And, in flow velocimetry, the velocity is derived from the motion of tracer particles. Thin-sheet illumination, as in particle image velocimetry (PIV), provides planewise data, unaffected by the numerous particles in other regions of the flow that remain in the dark. Recent interest concerns 3-D and non-stationary flows where a field of considerable spatial depth must be registered instantaneously. Pulsed holography has been introduced to record the deep field of small scattering particles. The velocity vectors are obtained from a detailed evaluation of the positions of reconstructed particle images. Under these conditions, however, the advantage of a dark region in front or behind the area of interest is sacrificed and optical noise deteriorates the evaluation.
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