Videogrammetric Methods in Velocimetry

Photogrammetry has been successfully applied in surveying and mapping for a long time. New imaging techniques, digital data acquisition and storage and powerful computing facilities transformed photogrammetry into videogrammetry, a technique applied in many fields for precise and reliable position measurements. Two applications of videogrammetry in fluid mechanics are presented in this article. Both are at their present stage of development suited for three-dimensional velocity measurements in liquids. One is based on tracking particles seeded in the liquid by using three to four synchronized video-cameras (PTV). It allows one to determine accurately the velocity vectors at a large number of points inside a thick observation volume and also to follow the trajectories of these particles for sufficiently long time periods. It is especially well suited for Lagrangian measurements in flows. The other tracks small three-dimensional patterns in flows of liquids tagged by fluorescent dye (LIFV). The three-dimensional Laser Induced Fluorescence images needed are obtained by sweeping rapidly a thin laser-light sheet with simultaneous imaging using a high speed solid-state camera. The method yields the shift and deformations of the liquid volumes associated with these patterns and allows one to determine velocity vectors and their derivatives simultaneously and accurately at a large number of points inside the observation volume. This review article includes 100 references.