High Density, Long-Term 3D PTV Using 3D Scanning Illumination and Telecentric Imaging

Abstract

This article discusses the application of 3D SPTV (3D Scanning Particle Tracking Velocimetry) to the high-density reconstruction of Lagrangian trajectories using telecentric imaging and a homogenous 3D illumination. A cubic volume in the order of roughly 10 x 10 x 10 cm³ is illuminated by a 3D beam scanning device and is recorded by three high speed digital cameras equipped with telecentric lenses. A vortex ring in a water tank is used as a model flow. The advantages of this setup are small particle displacements relative to the distances between the particles due to the high speed recording and a large depth of field without distortions due to the telecentric lenses. The scanning laser beam generates a homogenous and efficient illumination of the particles over the whole volume and a precise parallel shift of the scanned planes. The quality and precision of illumination and the telecentric imaging yield a more simplified particle matching and 3D reconstruction. This results in a robust, accurate and easy detection of time resolved particle trajectories with a high spatial resolution within the measured volume.