Investigation on Effect of Surface Roughness Pattern to Drag Force Reduction Using Rotary Rheometer

[+] Author and Article Information
Chen Haosheng

State Key Laboratory of Tribology, Tsinghua University, Beijing China 100084chenhs@mail.tsinghua.edu.cn

Chen Darong, Li Yongjian

State Key Laboratory of Tribology, Tsinghua University, Beijing China 100084

J. Tribol 128(1), 131-138 (Sep 16, 2005) (8 pages) doi:10.1115/1.2125969 History: Received June 12, 2005; Revised September 16, 2005

A drag force reduction experiment is performed on polyoxyethylene (PEO) water solution using a rotary rheometer. Longitudinal, transverse, and isotropic grooves are notched on the rotor’s surface to investigate the effect of surface roughness patterns. The experiment results show that higher drag force is generated on the surface with transverse grooves compared with the drag force on a smooth surface, while lower drag force is generated on the surface with longitudinal grooves. The drag force on the surface with isotropic grooves is between them. Forces on the side wall of the grooves play important roles in drag force reduction. They are numerically analyzed based on the Navier-Stokes equation using the finite volume method. The viscous force on the groove’s bottom plane is far less than the force on the corresponding plane of the smooth surface, but the drag force on the groove’s surface is compensated either by the pressure drag on the side walls of the transverse groove or by the viscous force on the side walls of the longitudinal groove. The pressure drag on side wall of transverse groove is always higher than the viscous force on side wall of longitudinal groove. The numerical results cope with the experiment results that only the surface with longitudinal grooves can reduce the drag force.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Geometry models of surface patterns. (a) Transverse pattern. (b) Longitudinal pattern. (c) Isotropic pattern.

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Figure 2

Solution viscosity and its fit line

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Figure 3

Measuring schematic and rotors with different surface roughness patterns. (a) Measurement schematic. (b) Surface with longitude grooves. (c) Surface with transverse grooves. (d) Surface with isotropic grooves.

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Figure 4

Effect of surface roughness patterns on shear force with different solutions. (a) 50 ppm PEO water solution, Molecular weight = 0.5 million. (b) 50 ppm PEO water solution, Molecular weight = 1 million. (c) 50 ppm PEO water solution, Molecular weight = 2.5 million. (d) 50 ppm PEO water solution, Molecular weight = 5 million.

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Figure 5

Pressure on the perpendicular planes of transverse groove

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Figure 6

Strain rate on the perpendicular planes

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Figure 7

Forces on planes of transverse and longitudinal grooves. (a) Total force comparison when velocity is 2 m/s. (b) Force comparison under different shear rates.

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Figure 8

Effect of surface pattern on drag reduction compared with smooth surface. (a) Comparison of drag force on different surfaces. (b) Strain rate along y direction.




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