Abstract
A new digital image processing system was constructed for three-dimensional particle tracking velocimetry, it consists of three TV cameras, three laser disk recorders, and a digital image processor interfaced with a graphic work station. A set of three images simultaneously taken by the cameras can be recorded consecutively at a 1/60s or 1/30s interval. A technique of particle path reconstruction over two to four time steps is introduced. A particle is. tracked by finding the particle in a search region around the particle's new position which is estimated from the preceding particle positions. The size of the search region must be large enough to capture all possible particle motions and, at the same time, smaller than the average particle distance to execute data processing efficiently. The optimization of this search region size is presently analyzed using the Lagrangian time spectra of velocity fluctuation. Computer simulations are also performed to evaluate effectiveness of the multiple time-step particle path reconstruction technique with modeled Lagrangian spectra of isotropic homogeneous turbulence.
