Computer aided measurement of velocity fields in liquid flows

This paper presents a computer aided measurement of velocity fields based on the hydrogen bubble method. This method uses streaks of hydrogen bubbles to trace how the water flows. The bubbles are generated in a transparent section of a pipe and the images are captured using a video camera with a stroboscopic lamp. The data collected is further processed off-line by a workstation. The processing comprises two main stages: image and data processing. In the first stage the electrode and hydrogen streaks are located and measured. The second stage performs a numerical processing of data and creates a graphical output. The software was used for processing sixteen sequences, each ten images long and 94.6% of all hydrogen streaks were measured correctly compared with manual processing. On a typical workstation, processing takes of the order of minutes compared with weeks of manual work. The paper describes these stages in details and shows the results.