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Research Papers: Alternative Energy Sources

Improvement of Aerodynamic Performance of Cambered Airfoils Using Leading-Edge Slots

[+] Author and Article Information
Saman Beyhaghi

Department of Mechanical Engineering,
University of Wisconsin-Milwaukee,
3200 N. Cramer Street,
Milwaukee, WI 53211
e-mail: beyhagh2@uwm.edu

Ryoichi S. Amano

Fellow ASME
Department of Mechanical Engineering,
University of Wisconsin-Milwaukee,
3200 N. Cramer Street,
Milwaukee, WI 53211
e-mail: amano@uwm.edu

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received September 27, 2016; final manuscript received February 9, 2017; published online March 16, 2017. Assoc. Editor: Ashwani K. Gupta.

J. Energy Resour. Technol 139(5), 051204 (Mar 16, 2017) (8 pages) Paper No: JERT-16-1388; doi: 10.1115/1.4036047 History: Received September 27, 2016; Revised February 09, 2017

Feasibility of increasing lift and decreasing drag by drilling narrow span-wide channels near the leading edge of NACA 4412 airfoils is investigated. It is proposed to drill two-segment slots that allow some of the incoming air to flow through them and then exit from the bottom surface of the airfoil. Such slots can result in an increased local pressure and thereby higher lift. Length, width, inlet angle, and exit angle of slots are varied to determine optimum configurations. Aerodynamic performance at different angles of attack (AoAs) and the chord-based Reynolds number of 1.6 × 106 is investigated. It is concluded that longer and narrower slots with exit streams more aligned with the air flowing below the airfoil can result in a higher lift. Also, in order to keep the slotted airfoils beneficial for AoAs greater than zero, it is proposed to (a) slightly lower the slot position with respect to the original design and (b) tilt up the first-leg by a few degrees. For the best design case considered, an average improvement of 8% is observed for lift coefficient over the entire range of AoA (with the maximum increase of 15% for AoA = 0), without any significant drag penalty.

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References

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Figures

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Fig. 1

The slotted wind turbine blade fabricated and tested at UWM Wind Tunnel

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Fig. 2

The computational domain and the mesh generated around a typical slotted airfoil: (a) geometry, (b) mesh around the airfoil, (c) mesh magnified near the leading edge and slot, and (d) mesh near the trailing edge

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Fig. 3

(a) A typical picture of a slotted airfoil considered for this study and (b) cross section of a slotted airfoil with five main geometric parameters shown

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Fig. 4

(a) Lift coefficient, (b) drag coefficient, and (c) pressure coefficient with negative sign at AoA = 0 deg

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Fig. 5

Results of a parametric study on (a) lift and (b) drag coefficients, as a function of slot first-leg length, slot width, and the exit angle

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Fig. 6

Performance of slotted airfoils with different slot widths in terms of (a) lift coefficient and (b) drag coefficient

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Fig. 7

Performance of slotted airfoils with different first-leg lengths in terms of lift and drag coefficients

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Fig. 8

Velocity vectors near a slotted airfoil with L1/c = 70%, w/c = 2%, β1 = 0 deg, β2 = 85 deg, and h/c = 4% operating under (a) AoA = 0 deg and (b) AoA = 8 deg

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Fig. 9

Lift and drag coefficients of slotted airfoils with different first-leg lengths, w/c = 1%, and β2 = 25 deg at different AoAs

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Fig. 10

Lift and drag coefficients of slotted airfoils with different slot widths, L1/c = 80%, and β2 = 25 deg at different AoAs

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Fig. 11

Pressure contours (near leading edge) and normalized velocity contours (near both leading and trailing edges) for a slotted airfoil with L1/c = 80%, w/c = 1%, β1 = 0 deg, β2 = 80 deg, and h/c = 5.5% at AoA = 0 deg

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Fig. 12

Performance of slotted airfoils with different relative exit angles β2, with L1/c = 80%, and w/c = 0.5%: (a) lift coefficient and (b) drag coefficient

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