A Vision-Based Particle Tracking Velocimetry

Particle Image Velocimetry (PIV) is a non-intrusive optical technique to measure velocity of flows. It provides the simultaneous visualization of the streamline pattern in unsteady flows and the quantification of the velocity field over the image plane. To reveal the flow motion, the flow is seeded by small scattering particles. The instantaneous fluid velocities are evaluated by recording the images of tracers, suspended in the flid and traversing a light sheet. A PIV system consists of seeding particles, illumination unit, image acquisition system, and a computer for image processing. For industrial applications a classical PIV system is not suitable for its cost, sizes and needs of specialised users and work areas. Moreover, classical PIV are unable to work in real-time for the huge amount of data and expensive algorithms adopted. In this paper, a study and the implementation of a new PIV system is described and compared against classical PIV solutions. The solution proposed is capable of working in real-time and is a Continuous PIV, CPIV, system: with respect to classical PIV, it is composed of a continuous laser light source and a CCD camera. A specifically new image-processing algorithm for velocity estimation and recognition of correct traces has been developed. It is based on the grey level distribution in the particle trace image, and indicates those particles moving with an out-of-plane velocity vector component and provides the measure with a limited error.