Visualizing Conduit Flows around Solitary Air Pockets by FVT and HSPIV
Publication: Journal of Engineering Mechanics
Volume 141, Issue 5
Abstract
Understanding flow characteristics around air pockets is fundamental in the study of air entrainment and transport in pipelines. This study deals with the use of flow visualization technique (FVT) and high-speed particle image velocimetry (HSPIV) in exploration of the characteristics around stationary air pockets in horizontal-pipe flow. The air-pocket volume varies from 0 to 10.0 mL, and the air pocket is injected into a fully developed turbulent flow with Reynolds numbers between 17,000 and 18,400. In the plane of symmetry, the main flow features include (1) a horseshoe vortex upstream, (2) a stagnation point on the frontal interface, (3) a separation point and a separated shear layer beneath, (4) a reattached shear layer downstream of the reattachment point (for air-pocket volumes greater than 2.0 mL), and (5) a reverse-flow region downstream. The deformable air pocket in the turbulent flow causes streamwise random movements of both the stagnation and separation points around their mean positions. The flow pattern is categorized based on the occurrence of either separated flow or flow reattachment. Fully separated flow (Mode I) occurs at air-pocket volumes less than 2.0 mL. Intermittently reattached flow (Mode II) occurs if the volume is within 2.0–5.0 mL. Fully reattached flow (Mode III) is evident at volumes greater than 5.0 mL. Water particles on the air-pocket surface move with the adjacent flow, thus forming a slip boundary. The evolution of mean streamwise velocity beneath the air pocket demonstrates the formation of either a separated or a reattached shear layer. Using nonlinear regression analysis, appropriate characteristic velocity and length scales are determined to obtain similarity profiles in the separated shear layer beneath.
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Acknowledgments
The experiments reported in this paper were conducted in the Hydraulic Laboratory of the Department of Civil Engineering, National Chung Hsing University (NCHU), Taiwan. This study, a cooperation between NCHU and the Royal Institute of Technology (KTH), is part of a research program in the area of hydraulic design funded in part by the Swedish Hydropower Centre [Svenskt Vattenkraftcentrum (SVC)], Stockholm. The authors are grateful to Mr. Cristian Andersson, of the SVC, for project coordination. Further, the authors also thank Dr. Ming-Jer Kao and Mr. Guang-Wei Tzeng, postdoctoral research fellow and master’s graduate student at NCHU, respectively, for their kind help in test rig installations as well as in modifications of the tables and figures in the revision.
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Published In
Journal of Engineering Mechanics
Volume 141 • Issue 5 • May 2015
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Jan 12, 2014
Accepted: Aug 14, 2014
Published online: Oct 1, 2014
Published in print: May 1, 2015
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