Evaluation and correction of perspective errors in endoscopic PIV

Results are presented from a single and dual lens endoscopic PIV imaging system with a view to application of PIV where optical access is restricted, such as internal combustion engines and other internal flows. PIV images taken from the single lens system were processed using cross-correlation and a quadratic distortion-mapping function. The dual lens images were processed using cross-correlation, a cubic mapping function, and standard stereoscopic relationships. Comparisons between the single and dual lens systems show the single lens system to have in-plane errors, caused by perspective effects, of an order of magnitude greater than the stereoscopic dual lens endoscopic PIV system. The stereo arrangement is recommended wherever quantitative velocimetry is required, and may also prove useful in general endoscopic inspection where dimensional measurements are to be estimated.