SIMULTANEOUS MEASUREMENT OF UNSTEADY FLOW VECTORS OVER LARGE REGIONS.

An important recent development in experimental fluid mechanics is the arrival of a new generation of optical instruments that provide fluid velocity vector data at several thousand points in a flow simultaneously. These instruments use a pulsed light source, typically a pulsed laser, to produce a multiple exposure photographic image of fine particles moving with the fluid. Analysis of the photograph to obtain the particle displacement between exposures then yields a vector map of the flow. Instruments under development differ from elementary photographic time-of-flight predecessors by virtue of very significant improvements in quantitative performance. The primary purpose of this presentation is to describe the principles and current status of two-dimensional, non-holographic pulsed laser velocimetry. However, much of the discussion pertains equally well to two-dimensional image planes obtained from holographic recordings.