Three-dimensional measurements of single bubble dynamics in a small diameter pipe using stereoscopic particle image velocimetry

The particle tracking velocimetry combined with the shadow image measurement techniques were used to study the velocity field generated by the passage of a single air bubble through a small volume, as it was rising in quiescent water, in a small diameter pipe. This technique provides the velocity field in conjunction with the bubble size and shape. The tracer particles were first tracked through foul consecutive frames, using a Hough transform and an architecture resonance theory 2 (ART 2) neural network. Then, the three-dimensional reconstruction of the how held in the whole measurement volume was achieved through a stereoscopic matching technique. Detailed information about the three-dimensional reconstruction of the bubble shape, calibration, particle tracking, and stereoscopic vector matching algorithms is presented. Error analysis to evaluate the accuracy of the measurements is also included. The effect of the wall on the flow field was studied by dividing the test volume into two regions; namely, center region and wall region. This allowed grouping similar bubble rise trajectories to perform conditional averages of the transient behavior of the velocity field. The vorticity generated from the velocity field is described and discussed for the bubble trajectory along the pipe core. (C) 2001 Elsevier Science Ltd. All rights reserved.