A Cost-efficient Shadow Particle Tracking Velocimetry Setup Suitable for Tracking Small Objects in a Large Volume

We use a Shadow Particle Tracking Velocimetry technique (S-PTV) with collimated light to investigate the dynamics of a turbulent von Kármán (VK) flow in water. Such a PTV technique permits easy calibration since the apparent particle positions on the images do not depend on the camera-particle distance and tracking of small objects (100 μm particles, fibers, ...) with low power LEDs light sources is made possible in a large volume (approximately (6 cm)3). This technique provides an ensemble of Lagrangian trajectories which are conditioned in space on a grid in order to reconstruct the 3d Eulerian mean flow together with its fluctuations. Typical Lagrangian statistics can also be obtained with this technique, such as velocity and acceleration auto-correlation functions.