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 measuremen t 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 quiesce nt water, in a small diameter pipe. This technique provides the velocity fi eld in conjunction with the bubble size and shape. The tracer particles wer e first tracked through foul consecutive frames, using a Hough transform an d an architecture resonance theory 2 (ART 2) neural network. Then, the thre e-dimensional reconstruction of the how held in the whole measurement volum e was achieved through a stereoscopic matching technique. Detailed informat ion about the three-dimensional reconstruction of the bubble shape, calibra tion, particle tracking, and stereoscopic vector matching algorithms is pre sented. 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 v olume 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 fr om the velocity field is described and discussed for the bubble trajectory along the pipe core. (C) 2001 Elsevier Science Ltd. All rights reserved.