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Open AccessArticle

Asymmetrical Velocity Distribution in the Drag-Reducing Channel Flow of Surfactant Solution Caused by an Injected Ultrathin Water Layer

by Zaiguo Fu 1,*, Xiaotian Liang 1 and Kang Zhang 2,*
1
College of Energy and Mechanical Engineering, Shanghai University of Electric Power, Shanghai 200090, China
2
Department of Thermal Engineering, Chengde Petroleum College, Chengde 067000, China
*
Authors to whom correspondence should be addressed.
Symmetry 2020, 12(5), 846; https://doi.org/10.3390/sym12050846
Received: 29 March 2020 / Revised: 14 May 2020 / Accepted: 15 May 2020 / Published: 21 May 2020
(This article belongs to the Special Issue Symmetry in Fluid Flow)
Although the turbulent intensity is suppressed in the drag-reducing channel flow by viscoelastic additives, the mean velocity distribution in the channel flow is symmetrical and tends to be similar to the laminar flow. In the study of near-wall modulation of the drag-reducing flow with an injected ultrathin water layer, an asymmetrical mean velocity distribution was found. To further investigate this phenomenon and the underlying cause, an experiment was carried out with the water injected from a porous channel wall at a small velocity (~10−4 m/s) into the drag-reducing flow of surfactant solution. The instantaneous concentration and flow fields were measured by using planar laser-induced fluorescence (PLIF) and particle imaging velocimetry (PIV) techniques, respectively. Moreover, analyses on turbulent statistical characteristics and spatial distribution of viscoelastic structures were carried out on the basis of comparison among various flow cases. The results showed that the injected ultrathin water layer under present experimental conditions affected the anisotropy of the drag-reducing flow. The characteristics, such as turbulence intensity, showed the zonal feature in the wall-normal direction. The Reynolds shear stress was enhanced in the near-wall region, and the viscoelastic structure was modified severely due to the redistributed stress. These results may provide experimental supports for the near-wall modulation of turbulence and the exploration of the drag-reducing mechanism by viscoelastic additives. View Full-Text
Keywords: drag-reducing flow; viscoelasticity; water layer; velocity distribution; modulation drag-reducing flow; viscoelasticity; water layer; velocity distribution; modulation
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MDPI and ACS Style

Fu, Z.; Liang, X.; Zhang, K. Asymmetrical Velocity Distribution in the Drag-Reducing Channel Flow of Surfactant Solution Caused by an Injected Ultrathin Water Layer. Symmetry 2020, 12, 846.

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