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.

Copyright © 2017 by ASME
Your Session has timed out. Please sign back in to continue.


Burton, T. , Jenkins, N. , Sharpe, D. , and Bossanyi, E. , 2011, Wind Energy Handbook, Wiley, Chichester, UK.
Heathcote, D. J. , Gursul, I. , and Cleaver, D. J. , 2016, “ An Experimental Study of Mini-Tabs for Aerodynamic Load Control,” AIAA Paper No. 2016-0325.
Martin, S. , and Bhushan, B. , 2014, “ Fluid Flow Analysis of a Shark-Inspired Microstructure,” J. Fluid Mech., 756, pp. 5–29. [CrossRef]
Bixler, G. D. , and Bhushan, B. , 2013, “ Fluid Drag Reduction With Shark-Skin Riblet Inspired Microstructured Surfaces,” Adv. Funct. Mater., 23(36), pp. 4507–4528. [CrossRef]
Troldborg, N. , Zahle, F. , and Sørensen, N. N. , 2015, “ Simulation of a MW Rotor Equipped With Vortex Generators Using CFD and an Actuator Shape Model,” AIAA Paper No. 2015-1035.
Gao, L. , Zhang, H. , Liu, Y. , and Han, S. , 2015, “ Effects of Vortex Generators on a Blunt Trailing-Edge Airfoil for Wind Turbines,” Renewable Energy, 76, pp. 303–311. [CrossRef]
Wang, C. , and Sun, M. , 2000, “ Separation Control on a Thick Airfoil With Multiple Slots Blowing at Small Speeds,” Acta Mech., 143(3–4), pp. 215–227. [CrossRef]
Johnson, S. J. , van Dam, C. P. , and Berg, D. E. , 2008, “ Active Load Control Techniques for Wind Turbines,” Sandia National Laboratories, Albuquerque, NM, Technical Report No. SAND2008-4809.
Subash, B. , Nithyapathi, C. , Manikandan, D. , and Murali, K. K. , 2014, “ Aerodynamic Optimization of Wind Turbine Blade by Employment of Slot to Counteract the Effect of Drag,” Int. J. Emerging Technol. Adv. Eng., 4(3), pp. 249–253.
Ibrahim, M. S. , Alsultan, A. , Shen, S. , and Amano, R. S. , 2015, “ Advances in Horizontal Axis Wind Turbine Blade Designs: Introduction of Slots and Tubercle,” ASME J. Energy Resour. Technol., 137(5), p. 051205. [CrossRef]
Alsultan, A. , 2015, “ Computational and Experimental Study on Innovative Horizontal-Axis Wind Turbine Blade Designs,” M.Sc. thesis, University of Wisconsin-Milwaukee, Milwaukee, WI.
Menter, F. R. , 1994, “ Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications,” AIAA J., 32(8), pp. 1598–1605. [CrossRef]
Wadcock, A. J. , 1978, “ Flying-Hot-Wire Study of Two-Dimensional Turbulent Separation on an NACA 4412 Airfoil at Maximum Lift,” Ph.D. thesis, California Institute of Technology, Pasadena, CA.
Rumsey, C., 2014, “ 2DN44: 2D NACA 4412 Airfoil Trailing Edge Separation,” NASA Langley Research Center, Hampton, VA, accessed Aug. 27, 2016, http://turbmodels.larc.nasa.gov/naca4412sep_val.html


Grahic Jump Location
Fig. 1

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

Grahic Jump Location
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

Grahic Jump Location
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

Grahic Jump Location
Fig. 4

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

Grahic Jump Location
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

Grahic Jump Location
Fig. 6

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

Grahic Jump Location
Fig. 7

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

Grahic Jump Location
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

Grahic Jump Location
Fig. 9

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

Grahic Jump Location
Fig. 10

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

Grahic Jump Location
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

Grahic Jump Location
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



Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In