Particle tracking velocimetry in three-dimensional flows

The photogrammetric determination of three-dimensional particle coordinates from a 3-camera system is described in Part I. In Part II we describe a fully automated tracking scheme for the determination of a sequence of velocity vectors within a three-dimensional observation volume of a fluid flow. From this sequence long-time particle trajectories are reconstructed.The tracking scheme is tested on trajectories obtained using the Kinematic Simulation Inertial Model (KSIM). Estimates of the yield of links between adjacent data sets of particle positions and of the yield of long-time particle trajectories are obtained. The limits of efficient tracking as a function of the spacing-displacement ratio p = _o/ut are also obtained. The effect of noise, in the form of the apparent appearance and disappearance of particles between one image and the next, and of jitter, which is the error in the determination of particle coordinates, is examined. It is shown that noise reduces the number of links per frame, but does not increase the number of erroneous links which is always small. However, the yield of long trajectories drops sharply with increasing noise. A small level of jitter, on the other hand, does not significantly influence any of the results.The tracking scheme is used on two sets of particle coordinate data obtained from real flows: a non-turbulent flow in a small water tank and a turbulent open channel flow.