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Research Papers

Drag Reduction Using Riblet Film Applied to Airfoils for Wind Turbines

[+] Author and Article Information
Agrim Sareen

Department of Aerospace Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: sareen2@illinois.edu

Robert W. Deters

Department of Aerospace Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: rdeters@illinois.edu

Steven P. Henry

Department of Aerospace Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: henry12@illinois.edu

Michael S. Selig

Associate Professor
e-mail: m-selig@illinois.edu
Department of Aerospace Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received November 7, 2011; final manuscript received June 16, 2013; published online September 16, 2013. Assoc. Editor: Christian Masson.

J. Sol. Energy Eng 136(2), 021007 (Sep 16, 2013) (8 pages) Paper No: SOL-11-1247; doi: 10.1115/1.4024982 History: Received November 07, 2011; Revised June 16, 2013

This paper presents results of a study that was commissioned by the 3M Renewable Energy Division to measure the drag reduction by using riblet film on airfoils specifically designed for wind turbine applications. The DU 96-W-180 airfoil was tested with four different symmetrical V-shaped riblet sizes (44, 62, 100, and 150-μm) at three Reynolds numbers (1 × 106, 1.5 × 106, and 1.85 × 106) and at angles of attack spanning the low drag range of the airfoil. Tests were run with riblet film covering different sections of the airfoil in order to determine the optimal riblet location in terms of drag reduction. Results showed that the magnitude of drag reduction depended on the angle of attack, Reynolds number, riblet size, and riblet location. For some configurations, riblets produced significant drag reduction of up to 5%, while for others riblets were detrimental. Trends in the results indicated an optimum riblet size of 62-μm for the range of Reynolds numbers at which tests were conducted. The airfoil chord was 18 in (0.457 m). Results also showed that each riblet size performed best at a given Reynolds number with the optimal Reynolds number decreasing with an increase in riblet size.

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References

Figures

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Fig. 1

Schematic of the UIUC low-turbulence subsonic wind tunnel

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Fig. 2

Riblet film viewed under a scanning electron microscope: a) 44-μm riblet film, and b) 62-μm riblet film (courtesy of 3 M)

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Fig. 3

Cp distribution for the DU 96-W-180 at Re = 1,500,000 as predicted by XFOIL

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Fig. 4

Drag polar for the DU 96-W-180 at Re = 1,500,000 as predicted by XFOIL

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Fig. 5

Flow visualization on the upper surface of the DU 96-W-180 airfoil at α = 6 deg and Re = 1,500,000

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Fig. 6

Laminar separation, reattachment and riblet film locations on the DU 96-W-180 airfoil at angles of attack near maximum L/D (symbols correspond to x/c locations and not airfoil surface normal)

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Fig. 7

Drag polars for the clean DU 96-W-180 at the three Re

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Fig. 8

Drag polar for the DU 96-W-180 at Re = 1,000,000 with 44-μm riblets in the turbulent regions

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Fig. 9

Drag polar for the DU 96-W-180 at Re = 1,000,000 with 62-μm riblets in the turbulent regions

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Fig. 10

Drag polar for the DU 96-W-180 at Re = 1,000,000 with 100-μm riblets in the turbulent regions

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Fig. 11

Drag polar for the DU 96-W-180 at Re = 1,000,000 with 150-μm riblets in the turbulent regions

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Fig. 12

Drag polar for the DU 96-W-180 at Re = 1,500,000 with 44-μm riblets in the turbulent regions

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Fig. 13

Drag polar for the DU 96-W-180 at Re = 1,500,000 with 62-μm riblets in the turbulent regions

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Fig. 14

Drag polar for the DU 96-W-180 at Re = 1,500,000 with 100-μm riblets in the turbulent regions

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Fig. 15

Drag polar for the DU 96-W-180 at Re = 1,500,000 with 150-μm riblets in the turbulent regions

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Fig. 16

Drag polar for the DU 96-W-180 at Re = 1,850,000 with 44-μm riblets in the turbulent regions

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Fig. 17

Drag polar for the DU 96-W-180 at Re = 1,850,000 with 62-μm riblets in the turbulent regions

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Fig. 18

Drag polar for the DU 96-W-180 at Re = 1,850,000 with 100-μm riblets in the turbulent regions

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Fig. 19

Drag polar for the DU 96-W-180 at Re = 1,850,000 with 150-μm riblets in the turbulent regions

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Fig. 20

Percent drag reduction variation with riblet size for the DU 96-W-180 at Re = 1,500,000 and riblets in the upper and lower surface turbulent regions

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Fig. 21

Percent drag reduction variation with riblet size for the DU 96-W-180 at Cl = 0.75 and riblets in the upper and lower surface turbulent regions

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