Off-axis holographic particle image velocimetry for diagnosing particulate flows

Holographic particle image velocimetry (HPIV) is a three-dimensional (3D) measurement technique that was originally developed for the velocity field measurements of single-phase fluid flows. The present study aims at a further extension of the HPIV technique for multiphase flow applications. HPIV should be able to provide not only the flow velocity fields on 3D grids, but also 3D information for individual particles including their positions and velocities. In this paper, we describe the extension of an off-axis HPIV system for the measurement of 3D positions and velocities of particles. Unlike most other PIV and HPIV systems, where velocity fields are obtained from correlation techniques, this HPIV system measures velocities by matching and pairing particles and potentially preserves the individual particle information. A volume rendering algorithm called the particle reconstructed by edge detection (PRED) method is developed to identify individual 3D particle images with complicated shapes. As a starting point of the development of HPIV for diagnosing particulate flows, this technique is applied to both a simulated flow to provide accuracy analysis and a real flow to test its feasibility.