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13th Int. Symp on Appl. Laser Techniques to Fluid Mechanics, Lisbon, Portugal, June 26 – 29, 2006 Application of 3D-PTV to track particle in fluid mechanics experiments Antonio Cenedese1, John H. Cushman2 and Moroni Monica1 1: DITS – University of Rome “La Sapienza”, Italy 2: Mathematics Department - Purdue University, Italy Keywords: 3D-PTV processing, particle tracking 1. Introduction 3. Results There exist a number of imaging-based measurement techniques for determining 3D velocity fields in an observation volume. Among these are: • scanning techniques; • holographic techniques; • defocusing techniques; • photogrammetric techniques; • Feature-tracking techniques FT. We modify photogrammetric 3D-PTV by using feature tracking. The reconstruction of position and object shapes from photographs requires the camera/test section geometry be known. The system must be calibrated, then correspondences must detected to determine the 3D position of the tracer particles and finally, 3D trajectories are reconstructed via a tracking algorithm similar to the one used in the 2D reconstruction of Moroni and Cushman (2001). The time integral scales for two sets of data are presented in Tab. 1 while the velocity correlation functions are presented in figure 2. We will focus our attention on 3D-PTV which is an experimental technique based on reconstructing 3D trajectories of reflecting generic image features through a photogrammetric recording of image sequences. Feature coordinates are determined first and then trajectories are defined. 3D-PTV requires a lighted volume of the test section as opposed to 2D techniques that require a light sheet. 1/e 3 giri 6 giri Txx (s) 0.8392 1.7791 Tyy (s) 0.6657 1.5873 Tzz (s) 4.3893 2.1154 2. Experimental set-up Outlined in Figure 1 is the hexagonal cell (side length 24 cm, height 60 cm). As we are using an optical system based on visible light, the porous matrix within the test section and the fluid that bathes the matrix must be transparent to visible light. Moreover, both the matrix and the fluid must have the same refractive index so that matrix- fluid interface does not scatter light. For a tracer we will continue the use of small (<0.1 m) air bubbles for our Pyrex/glycerol mixtures and fluorescent micro-beads for the cryolite/water systems. Fig. 2 Comparison of velocity correlations along the principal axes for two sets of data Fig. 1 Hexagonal test section 16.5