Experimental error analysis of a digital angular stereoscopic PIV system is presented. The paper firstly describes an experimental rig which includes the design of a novel PIV test block for in situ calibration. This allowed the user to set up a static seeded flow volume which was translated in and out of plane to record PIV images using two megapixel CCD cameras positioned for angular stereoscopic viewing. PIV data were collected for a range of camera angles up to and for a range of flow displacements and processed by cross correlation into a set of two-dimensional calibration and flow displacement vectors. These 2D data were then processed into three-dimensional data by the use of geometric and bicubic spline interpolation algorithms and an error analysis performed on the predicted displacements. Results from this analysis have shown optimum system performance will be obtained by using camera angles of between 20 and and f numbers of f16 and higher. The results have also shown a theoretical prediction of system performance derived in previous work, which considers the ratio of out of plane to in plane errors, matches to within 8 and 18% of the experimental system performance.

A geometric error model for analysis and design of stereoscopic PIV systems is presented. The model allows displacement errors in either translational or angular systems to be analysed for any given angle or camera separation and for any off-axis position. A parameter for the analysis of the system performance is also introduced based on the ratio of out-of-plane to in-plane errors. This is subsequently used to investigate the relative performance of translational and angular PIV systems for camera angles up to and camera separations of half the object distance. Results from this analysis show similar trends in centreline characteristics for both types of stereo systems but different trends in off-axis error ratios due to imaging geometry. The results have also suggested that a CCD-based angular PIV stereo system offers up to 40% greater out-of-plane accuracy for a given field of view and laser power than previous translational systems.

No abstract