A high-performance system for 3-dimensional particle tracking velocimetry in turbulent flow research using image sequences

The standard method in turbulent flow measurement is Laser Doppler Anemometry. which gains only 2-dimen- sional information about the velocity with good accuracy, but only for stationary points. 3D-PTV is able to cover all three components of a spatial flow field using stereoscopic image sequences. The determination of the 3rd component of the velocity vector requires the solving of the stereo correspondence problem. In contrast to other methods which solve first the stereo correspondence for single images and do the particle tracking as a second step, this paper describes a high-performance algorithm working on image sequences, where the first step is the particle tracking and then in a second step the stereo correspondence problem is resolved for particle trajectories not for single particles. The advantage of this approach are the ability to track the particles for long time intervals (7-10 s and more) while the stereo correspondence has a matching rate between 90% and 100% at particle densities up to750 particles and still a matching rate of 65% at 2000 particles. The typical computation times on a Silicon Graphics Indy (MIPS R4000.100MHz) are 0.25 seconds/image for the particle tracking and 10 seconds for the stereo correspondence with sequences of 150 images and 350 particels. These are considerable short times. The system has been developed using real image sequences. In a second step simulated data has been evaluated and it can be shown, that the limitations of the system come from the particle tracking. Thus further study will focus on improvement of the particle tracking