Abstract
A technique for measuring the three components of velocity in liquid flows is developed by using a digital image processing system. This system consists of two Coupled Charged Device (CCD) cameras, a digital image processor interfaced with a micro-computer, and a stroboscope triggered by the CCD camera. Based on stereoscopic photography theory, the instantaneous three dimensional position of a tracer in a liquid flow is calculated by the relation between absolute and image coordinate systems, which is established by camera calibration. The present algorithm is verified by a preliminary experiment using a rotating solid model, and the associated uncertainty is evaluated systematically. An unsteady laminar Couette flow between two concentric cylinders, of which the outer cylinder starts to rotate impulsively, is measured by the present technique. Good agreement between the experimental and numerical results of instantaneous velocity distributions demonstrates the validity of the present technique for the application to the measurement in unsteady three-dimensional shear flows.
