STUDY OF THE PHENOMENA AFFECTING THE ACCURACY OF A VIDEO-BASED PARTICLE TRACKING VELOCIMETRY TECHNIQUE

The development of a video-based Particle Tracking Velocimetry (PTV) t echnique has focused on the problem of the accuracy of this method. Th e PTV-method can be decomposed into three parts: the recording of the experiment, the image processing and the evaluation of the velocities. The accuracy of each stage has been studied. Inaccuracies due to reso lution, length scale, light intensity and distortion of the x and y di rection are analysed. One of the main factors influencing the accuracy is the selection of the time difference between frames. During the ev aluation of velocities, incorrect identifications of particles may occ ur. The relation between the time-step of the frames and the percentag e of incorrect identifications has been shown. The percentage of false identifications increases with the size of the time-step. The resolut ion accuracy is however improved when the time-step is increased. An a dequate selection of the time-step has to be made to obtain a high res olution accuracy and a limited number of incorrect identifications.