Shear Layers in the Turbulent Pipe Flow of Drag Reducing Polymer Solutions
File(s)ZadraziletalChemEngSci2012_AAM.pdf (3.15 MB)
Accepted version
Author(s)
Zadrazil, I
Bismarck, A
Hewitt, GF
Markides, CN
Type
Journal Article
Abstract
A range of high molecular weight polymers (polyethylene oxide) was dissolved at very low concentrations – in the order of few wppm – in a solvent (water). The Newtonian character of the polymer solutions was confirmed by rheological measurements. The polymer solutions were then pumped through a long horizontal pipe section in fully developed turbulent conditions. The flow experienced a reduction in frictional drag when compared to the drag experienced by the equivalent flow of the pure solvent. Specifically, drag reduction was measured at Reynolds numbers ranging from 3.5×10^4 to 2.1×10^5 in a pressure driven flow facility with a circular tube section of internal diameter 25.3 mm. The turbulent flow was visualized by Particle Image Velocimetry and the resulting data were used to investigate the effect of the drag reducing additives on the turbulent pipe flow. Close attention was paid to the mean and instantaneous velocity fields, as well as the two-dimensional vorticity and streamwise shear strain rate. The results indicate that drag reduction is accompanied by the appearance of “shear layers” (i.e. thin filament-like regions of high spatial velocity gradients) that act as interfaces separating low-momentum flow regions near the pipe wall and high-momentum flow regions closer to the centerline. The shear layers are not stationary. They are continuously formed close to the wall at a random frequency and move towards the pipe centerline until they eventually disappear, thus occupying or existing within a “shear layer region”. It is found that the mean thickness of the shear layer region is correlated with the measured level of drag reduction. The shear layer region thickness is increased by the presence of polymer additives when compared to the pure solvent, in a similar way to the thickening of the buffer layer. The results provide valuable insights into the characteristics of the turbulent pipe flow of a solvent containing drag reducing polymers that can be used to further our understanding of the role of polymers on the mechanism of drag reduction and to develop advanced drag reduction models.
Date Issued
2012-01-08
Citation
Chemical Engineering Science, 2012, 72, pp.142-154
ISSN
0009-2509
Publisher
Elsevier
Start Page
142
End Page
154
Journal / Book Title
Chemical Engineering Science
Volume
72
Copyright Statement
Crown copyright © 2012 Published by Elsevier Ltd. All rights reserved. NOTICE: this is the author’s version of a work that was accepted for publication in Chemical Engineering Science. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Chemical Engineering Science, vol. 72, 2012. DOI:10.1016/j.ces.2011.12.044
Identifier
http://www3.imperial.ac.uk/people/c.markides
Subjects
Drag reduction
Hydrodynamics
Pipe flow
Polymers
Turbulence
Visualization
Publication Status
Published