Computer-aided discrimination of slow and fast tracer paths

An optical method for the discrimination between slow and fast tracer particles convected within a flow is proposed. It is based on the dependence of the brightness of a trace on the velocity of the corresponding tracer. The images of the traces are captured by a CCD-camera and processed on-line. A practical application of this technique to the visualization of the low velocity streamlines in a rotating duct is presented. The possibilities to develop this technique into a quantitative tool for velocity measurements is discussed.