Velocity-Field Measurement of a Vortex by Dynamic Image Processing

A new dynamic image processing technique is applied to the measurement of the velocity of a vortex flow. Velocity-field of the vortex (i.e., the spatial distribution of speed and that of moving direction) is measured and visualized by pixel-based analysis calculating the mutual-correlation functions among temporal brightness changes at each pixel. It is shown that the dependence of the measured local speed V on the distance from the center of the vortex r is approximately V\varpropto(1/r), consistent with the results of pioneers in the field.