Verification of 3-D Stereoscopic PIV Operation and Procedures

Particle image velocimetry (PIV) is a non-intrusive, whole-field velocity measurement technique that has been used since the mid-1980s. The accuracy, flexibility and versatility offered by PIV systems have made them extremely valuable tools for flow studies. 3-D stereoscopic PIV is the package capable of measuring 3-dimensional velocity components. It involves a very sophisticated routine during setup, calibration, measurement and data processing phases. This paper aims to verify the procedures of operation used for 3-D stereoscopic PIV measurements. This is important to ensure that the best data representation with low associated uncertainty is obtained. A free-diffuser inlet of rectangular cross-section, 14.2 cm x 6.2 cm, with known local air velocities (i.e. measured using pitot-static probe), is presently considered. The flow is assumed to be fully developed turbulent since sufficient hydrodynamic entry length, 4.4DhRe1/6< Lh,turb < 50Dh and Reynolds Number, Re>10000 are introduced. Images that are captured by CCD cameras are interpreted using Dantec Dynamic software providing 3-dimensional velocity vectors. The velocities obtained from PIV and pitot-static probe are compared in order to justify the quality of PIV measurement. The range of velocity obtained using probe is 2.31 – 2.58 m/s, whereas using PIV is 2.31 – 2.91 m/s. It thus gives the average discrepancy of 0.8%. Besides, there is also a close agreement between the air velocities measured by PIV and theories with average discrepancy of 1.2%. This discrepancy is mainly due to some uncertainties in the experiments such as imperfect matching of coordinate between probe and laser sheet, unsteadiness of flow, variation in density and less precision in calibration. The operating procedures of 3-D stereoscopic PIV have successfully been verified thus are justified to be used for future PIV measurement, provided minor discrepancies are recorded.