PARTICLE TRACKING VELOCIMETRY IN 3-DIMENSIONAL FLOWS .2. PARTICLE TRACKING

The photogrammetric determination of three-dimensional particle coordi nates from a 3-camera system is described in Part I. In Part II we des cribe a fully automated tracking scheme for the determination of a seq uence of velocity vectors within a three-dimensional observation volum e of a fluid flow. From this sequence long-time particle trajectories are reconstructed. The tracking scheme is tested on trajectories obtai ned using the Kinematic Simulation Inertial Model (KSIM). Estimates of the yield of links between adjacent data sets of particle positions a nd of the yield of long-time particle trajectories are obtained. The l imits of efficient tracking as a function of the spacing-displacement ratio p = DELTA0/u'DELTAt are also obtained. The effect of noise, in t he form of the apparent appearance and disappearance of particles betw een one image and the next, and of jitter, which is the error in the d etermination of particle coordinates, is examined. It is shown that no ise reduces the number of links per frame, but does not increase the n umber of erroneous links which is always small. However, the yield of long trajectories drops sharply with increasing noise. A small level o f jitter, on the other hand, does not significantly influence any of t he results. The tracking scheme is used on two sets of particle coordi nate data obtained from real flows: a non-turbulent flow in a small wa ter tank and a turbulent open channel flow.