Investigation on image processing error in Moire deflectometry applied to mini/micro scale flow visualization

摘要

When Moire deflectometry is used for mini/micro scale flow visualization, the phase variation caused by the non-uniform flow field is originally fairly small in magnitude. It is therefore essential, in order to meet the requests of mini/micro scale measurement, to reduce the error in image processing of Moire fringes to an acceptably small magnitude. In this paper, an effort has been made to explore the cause of image processing error with an emphasis on topics concerning the frequency leakage in Fourier transform and the request for operation parameters of measurement arrangement. Both mathematical analysis and numerical analogue are presented herewith. The research has shown that the following measures could help decrease the image processing error: (1) the Moire fringe should be externally interpolated so as to make it an integral multiple of fringe period; (2) the ratio of the cross angle of the two gratings to the distance between these gratings should be accordingly adjusted to conform with the deflect angle gradient.