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SPECIAL SECTION ON RANS/LES/DES/DNS: THE FUTURE PROSPECTS OF TURBULENCE MODELING

DNS of Drag-Reducing Turbulent Channel Flow With Coexisting Newtonian and Non-Newtonian Fluid

[+] Author and Article Information
Bo Yu

Department of Oil and Gas Storage and Transportation Engineering, China University of Petroleum, Beijing, 102249, People’s Republic of China

Yasuo Kawaguchi

Institute for Energy Utilization, National Institute of Advanced Industrial Science and Technology, Ibaraki 305-8564, Japan

J. Fluids Eng. 127(5), 929-935 (Jun 16, 2005) (7 pages) doi:10.1115/1.2012500 History: Received August 17, 2004; Revised June 16, 2005

In the present study, we numerically investigated drag-reducing turbulent channel flows by surfactant additives. Surfactant additives were assumed to be uniformly distributed in the entire flow region by turbulent convection and diffusion, etc., but it was assumed that the shear-induced structure (SIS) (network of rod-like micelles) could form either in the region next to the walls or in the center region of the channel, making the fluid viscoelastic. In other regions surfactant additives were assumed to be incapable of building a network structure, and to exist in the form of molecules or micelles that do not affect the Newtonian properties of the fluid. With these assumptions, we studied the drag-reducing phenomenon with coexisting Newtonian and non-Newtonian fluids. From the study we identified the effectiveness of the network structures at different flow regions, and showed that the phenomenon of drag-reduction (DR) by surfactant additives is not only closely associated with the reduction of Reynolds shear stress but also related to the induced viscoelastic shear stress.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Bilayer model of flows with Newtonian and non-Newtonian fluid coexistence. The gray color represents non-Newtonian fluid and the white color represents Newtonian fluid. The thickness of the non-Newtonian region is δ for flow A in the center region, and δ∕2 in the near-wall region for flow B.

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Figure 2

Local fractional contribution to the drag-reduction rate

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Figure 3

Mean velocity profiles

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Figure 4

The rms of streamwise velocity fluctuations

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Figure 5

The rms of wall-normal velocity fluctuations

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Figure 6

The rms of spanwise velocity fluctuations

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Figure 7

Budget of shear stress

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Figure 8

A comparison of Reynolds shear stresses

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Figure 9

Drag-reduction rate versus Reynolds number

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Figure 10

Relationships between DR%∕DR%max and Reb∕Rebmax

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