QUANTITATIVE FLOW-ANALYSIS AROUND AQUATIC ANIMALS USING LASER SHEET PARTICLE IMAGE VELOCIMETRY

Two alternative particle image velocimetry (PIV) methods have been dev eloped, applying laser light sheet illumination of particle-seeded flo ws around marine organisms, Successive video images, recorded perpendi cular to a light sheet parallel to the main stream, were digitized and processed to map the how velocity in two-dimensional planes, In parti cle tracking velocimetry (PTV), displacements of single particles in t wo subsequent images were determined semi-automatically, resulting in flow diagrams consisting of non-uniformly distributed velocity vectors , Application of grid-cell averaging resulted in pow field diagrams wi th uniform vector distribution, In sub-image correlation PIV (SCPIV), repetitive convolution filtering of small sub-areas of two subsequent images resulted in automatic determination of cross-correlation peaks, yielding flow field diagrams with regularly spaced velocity vectors, In both PTV and SCPIV, missing values, caused by incomplete particle d isplacement information in some areas of the images or due to rejectio n of some erroneous vectors by the vector validation procedure, were i nterpolated using a two-dimensional spline interpolation technique. Th e resultant vector how fields were used to study the spatial distribut ion of velocity, spatial acceleration, vorticity, strain and shear, Th ese flow fields could also be used to test for flow in the third dimen sion by studying the divergence, and to detect the presence and locati on of vortices, The results offer detailed quantitative descriptions o f the flow morphology and can be used to assess dissipated energy, The versatile character of the technique makes it applicable to a wide ra nge of fluid mechanical subjects within biological research, So far it has been successfully applied to map the flow around swimming copepod s, fish larvae and juvenile fish and the ventilation current of a tube -living shrimp.