DISTORTION COMPENSATION FOR GENERALIZED STEREOSCOPIC PARTICLE IMAGE VELOCIMETRY

Optical distortion due to inaccurate optical alignment, lens nonlinear ity, and/or refraction by optical windows, fluid interfaces, and other optical elements of an experiment causes inaccuracy by introducing va riable magnification. Since fractional changes in the magnification ha ve a one-to-one effect on the accuracy of measuring the velocity, it i s important to compensate for such distortions. A general experimental calibration procedure is described which determines the magnification matrix of a distorted imaging system, and an algorithm is presented t o compute accurate velocity field displacements from measurements of d istorted PIV images. These procedures form a basis for generalized ste reoscopic PIV procedures which permit easy electronic registration of multiple cameras and accurate recombination of stereoscopic displaceme nt fields to obtain the three-dimensional velocity vector field.