Research Papers

Experimental Investigation of the Effects of Winglets on the Tip Vortex Behavior of a Model Horizontal Axis Wind Turbine Using Particle Image Velocimetry

[+] Author and Article Information
Yaşar Ostovan

Department of Aerospace Engineering,
METU Center for Wind Energy,
Middle East Technical University (METU),
Ankara 06800, Turkey
e-mail: yasar.ostovan@centralelille.fr

M. Tuğrul Akpolat

Department of Aerospace Engineering,
METU Center for Wind Energy,
Middle East Technical University (METU),
Ankara 06800, Turkey
e-mail: tugrul.akpolat@metu.edu.tr

Oğuz Uzol

Department of Aerospace Engineering,
METU Center for Wind Energy,
Middle East Technical University (METU),
Ankara 06800, Turkey
e-mail: uzol@metu.edu.tr

1Present address: Research Engineer at Laboratoire des Fluides de Lille Kampe de Feriet (LMFL), Villeneuve d'Ascq 59650, France,

2Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received September 21, 2017; final manuscript received August 4, 2018; published online September 14, 2018. Assoc. Editor: Yves Gagnon.

J. Sol. Energy Eng 141(1), 011006 (Sep 14, 2018) (13 pages) Paper No: SOL-17-1391; doi: 10.1115/1.4041154 History: Received September 21, 2017; Revised August 04, 2018

This study presents an experimental investigation on the effects of winglets on the near wake flow around the tip region and on the tip vortex characteristics downstream of a 0.94 m diameter three-bladed horizontal axis wind turbine (HAWT) rotor. Phase-locked 2D particle image velocimetry (PIV) measurements are performed with and without winglets covering 120 deg of azimuthal progression of the rotor. The impact of using winglets on the flow field near the wake boundary as well as on the tip vortex characteristics such as the vortex convection, vortex core size, and core expansion as well as the resultant induced drag on the rotor are investigated. Results show that winglets initially generate an asymmetric co-rotating vortex pair, which eventually merge together after about ten tip chords downstream to create a single but nonuniform vortex structure. Mutual induction of the initial double vortex structure causes a faster downstream convection and a radially outward motion of tip vortices compared to the baseline case. The wake boundary is shifted radially outward, velocity gradients are diffused, and vorticity and turbulent kinetic energy levels are significantly reduced across the wake boundary. The tip vortex core sizes are three times as big compared to those of the baseline case, and within the vortex core, vorticity and turbulent kinetic energy levels are reduced more than 50%. Results show consistency with various vortex core and expansion models albeit with adjusted model coefficients for the winglet case. The estimated induced drag reduction is about 15% when winglets are implemented.

Copyright © 2019 by ASME
Your Session has timed out. Please sign back in to continue.


Sohn, M. H. , and Chang, J. W. , 2012, “Visualization and PIV Study of Wing-Tip Vortices for Three Different Tip Configurations,” Aerosp. Sci. Technol., 16(1), pp. 40–46. [CrossRef]
Johansen, J. , and Sørensen, N. , 2006, “Aerodynamic Investigation of Winglets on Wind Turbine Blades Using CFD,” Risø National Laboratory, Roskilde, Denmark, Report No. Risø-R-1543(EN). http://cms.education.gov.il/NR/rdonlyres/D9F6FC7B-A508-43C8-BB34-5C6D8AE0346D/178684/risr1543.pdf
Gaunaa, M. , and Johansen, J. , 2007, “Determination of the Maximum Aerodynamic Efficiency of Wind Turbine Rotors With Winglets,” J. Phys. Conf. Ser., 75, p. 012006. [CrossRef]
Gertz, D. , Johnson, D. A. , and Swytink-Binnema, N. , 2012, “An Evaluation Testbed for Wind Turbine Blade Tip Designs - Winglet Results,” Wind Eng., 36(4), pp. 389–410. [CrossRef]
Elfarra, M. A. , Sezer-Uzol, N. , and Akmandor, I. S. , 2014, “NREL VI Rotor Blade: Numerical Investigation and Winglet Design and Optimization Using CFD,” Wind Energy., 17(4), pp. 605–626. [CrossRef]
Tobin, N. , Hamed, A. , and Chamorro, L. , 2015, “An Experimental Study on the Effects of Winglets on the Wake and Performance of a Model Wind Turbine,” Energies., 8(10), pp. 11955–11972. [CrossRef]
Shimizu, Y. , Ismaili, E. , Kamada, Y. , and Maeda, T. , 2003, “Power Augmentation of a HAWT by Mie-Type Tip Vanes, Considering Wind Tunnel Flow Visualisation, Blade-Aspect Ratios and Reynolds Number,” Wind Eng., 27(3), pp. 183–194. [CrossRef]
Abdulrahim, A. , Anik, E. , and Uzol, O. , 2016, “Effects of Mie Vanes and Tip Injection on the Performance and Wake Characteristics of a HAWT,” AIAA Paper No. 2016-0519. https://arc.aiaa.org/doi/10.2514/6.2016-0519
Ostovan, Y. , and Uzol, O. , 2016, “Experimental Study on the Effects of Winglets on the Performance of Two Interacting Horizontal Axis Model Wind Turbines,” J. Phys. Conf. Ser., 753, p. 022015. [CrossRef]
Grant, I. , Mo, M. , Pan, X. , Parkin, P. , Powell, J. , Reinecke, H. , Shuang, K. , Coton, F. , and Lee, D. , 2000, “An Experimental and Numerical Study of the Vortex Filaments in the Wake of an Operational, Horizontal-Axis, Wind Turbine,” J. Wind Eng. Ind. Aerodyn., 85(2), pp. 177–189. [CrossRef]
Xiao, J. P. , Wu, J. , Chen, L. , and Shi, Z. Y. , 2011, “Particle Image Velocimetry (PIV) Measurements of Tip Vortex Wake Structure of Wind Turbine,” Appl. Math. Mech. (English Ed.), 32(6), pp. 729–738. [CrossRef]
Massouh, F. , and Dobrev, I. , 2014, “Investigation of Wind Turbine Flow and Wake,” J. Fluid Sci. Technol., 9, pp. 167–176. [CrossRef]
Krogstad, P. Å. , and Lund, J. A. , 2012, “An Experimental and Numerical Study of the Performance of a Model Turbine,” Wind Energy., 15(3), pp. 443–457. [CrossRef]
Krogstad, P. Å. , and Eriksen, P. E. , 2013, “Blind Test” Calculations of the Performance and Wake Development for a Model Wind Turbine,” Renewable Energy, 50, pp. 325–333. [CrossRef]
Pierella, F. , Krogstad, P. Å. , and Sætran, L. , 2014, “Blind Test 2 Calculations for Two in-Line Model Wind Turbines Where the Downstream Turbine Operates at Various Rotational Speeds,” Renewable Energy, 70, pp. 62–77. [CrossRef]
Krogstad, P. Å. , Sætran, L. , and Adaramola, M. S. , 2015, “Blind Test 3” Calculations of the Performance and Wake Development behind Two in-Line and Offset Model Wind Turbines,” J. Fluids Struct., 52, pp. 65–80. [CrossRef]
Anik, E. , Abdulrahim, A. , Ostovan, Y. , Mercan, B. , and Uzol, O. , 2014, “Active Control of the Tip Vortex: An Experimental Investigation on the Performance Characteristics of a Model Turbine,” J. Phys. Conf. Ser., 524, p. 012098. [CrossRef]
Abdulrahim, A. , Anik, E. , Ostovan, Y. , and Uzol, O. , 2016, “Effects of Tip Injection on the Performance and Near Wake Characteristics of a Model Wind Turbine Rotor,” Renewable Energy., 88, pp. 73–82. [CrossRef]
Maughmer, M. D. , Swan, T. S. , and Willits, S. M. , 2002, “Design and Testing of a Winglet Airfoil for Low-Speed Aircraft,” J. Aircr., 39(4), pp. 654–661. [CrossRef]
Keane, R. D. , and Adrian, R. J. , 1991, “Optimization of Particle Image Velocimeters—II: Multiple Pulsed Systems,” Meas. Sci. Technol., 2, pp. 963–974.
Raffel, M. , Willert, C. E. , Scarano, F. , Kähler, C. J. , Wereley, S. T. , and Kompenhans, J. , 2018, Particle Image Velocimetry, Springer International Publishing, Cham, Switzerland.
Uzol, O. , and Camci, C. , 2001, “The Effect of Sample Size, Turbulence Intensity and the Velocity Field on the Experimental Accuracy of Ensemble Averaged PIV Measurements,” DLR-Mitteilung, pp. 1457–1465.
Uzol, O. , Chow, Y.-C. , Katz, J. , and Meneveau, C. , 2002, “Experimental Investigation of Unsteady Flow Field Within a Two-Stage Axial Turbomachine Using Particle Image Velocimetry,” ASME J. Turbomach., 124(4), p. 542. [CrossRef]
Van der Wall, B. G. , and Richard, H. , 2006, “Analysis Methodology for 3C-PIV Data of Rotary Wing Vortices,” Exp. Fluids., 40(5), pp. 798–812. [CrossRef]
Devenport, W. J. , Vogel, C. M. , and Zsoldos, J. S. , 1999, “Flow Structure Produced by the Interaction and Merger of a Pair of Co-Rotating Wing-Tip Vortices,” J. Fluid Mech., 394, pp. 357–377. [CrossRef]
Romeos, A. , Giannadakis, A. , Perrakis, K. , and Panidis, T. , 2016, “Co-Rotating Vortex Interaction,” Aircr. Eng. Aerosp. Technol., 88(2), pp. 285–293. [CrossRef]
Rankine, W. J. M. , 1858, Manual of Applied Mechanics, C. Griffen Co., London.
Oseen, C. W. , 1911, “Über Wirbelbewegung in Einer Reibenden Flüssigkeit,” Ark. Foer Mat. Astron. Och Fys., 7, pp. 1–13.
Scully, M. P. , 1975, “Computation of Helicopter Rotor Wake Geometry and Its Influence on Rotor Harmonic Airloads,” Ph.D. thesis, Massachusetts Institute of Technology, Cambridge, MA. https://dspace.mit.edu/handle/1721.1/64826
Vatistas, G. H. , Kozel, V. , and Mih, W. C. , 1991, “A Simpler Model for Concentrated Vortices,” Exp. Fluids., 11(1), pp. 73–76. [CrossRef]
Vatistas, G. H. , 2006, “Simple Model for Turbulent Tip Vortices,” J. Aircr., 43(5), pp. 1577–1579. [CrossRef]
Sant, T. , van Kuik, G. , and van Bussel, G. J. W. , 2006, “Estimating the Angle of Attack From Blade Pressure Measurements on the NREL Phase VI Rotor Using a Free Wake Vortex Model:axial Conditions,” Wind Energy., 9(6), pp. 549–577. [CrossRef]
Birch, D. , Lee, T. , Mokhtarian, F. , and Kafyeke, F. , 2004, “Structure and Induced Drag of a Tip Vortex,” J. Aircr., 41(5), pp. 1138–1145. [CrossRef]
Kusunose, K. , 1997, “Development of a Universal Wake Survey Data Analysis Code,” AIAA Paper No. AIAA-97-2294. https://arc.aiaa.org/doi/abs/10.2514/6.1997-2294


Grahic Jump Location
Fig. 1

(a) Model wind turbine located at the jet exit of the open jet wind tunnel and (b) the winglets attached to blade tips of the turbine

Grahic Jump Location
Fig. 2

Inlet velocity and turbulence intensity distributions 0.5D downstream of the open jet tunnel. Here R is the rotor radius. The rotor tip and the tunnel boundary positions are indicated on the figure.

Grahic Jump Location
Fig. 3

Definitions of winglet design variables

Grahic Jump Location
Fig. 4

(a) Phase definitions and sample three phases and (b) PIV measurement domain

Grahic Jump Location
Fig. 5

Convergence plot for two measured velocity components (left) as well as for turbulent kinetic energy (right) using samples from a grid point in window 1, for phase 90 and near the vortex core

Grahic Jump Location
Fig. 6

Picture of the facility while performing phase-locked PIV measurements

Grahic Jump Location
Fig. 7

(a) A sample PIV raw image for the baseline case at phase Φ = 36 deg, (b) and (c) corresponding phase averaged u¯ velocity and out-of-plane vorticity distributions near the blade tip, respectively, superimposed by vortex-induced velocity vectors. The free stream flow is from left to right. The dashed rectangular region represents the blade position at phase Φ = 0 deg. (x′/R)=(y′/R)=0 is the position of the blade tip at phase Φ = 0 deg.

Grahic Jump Location
Fig. 8

Phase-averaged axial velocity (u¯) distributions for rotor phases 0–120 deg for baseline (left) and winglet (right) cases

Grahic Jump Location
Fig. 9

Phase-averaged out-of-plane vorticity (ΩZ¯) distributions for rotor phases 0–120 deg for baseline (left) and winglet (right) cases. Vortex-induced velocity vectors are superimposed on the distributions.

Grahic Jump Location
Fig. 10

Phase-averaged turbulent kinetic energy distributions for rotor phases 0–120 deg for baseline (left) and winglet (right) cases

Grahic Jump Location
Fig. 11

Overall average of 21 phases (0–120 deg with 6 deg intervals) for (a) axial velocity, (b) vorticity, and (c) turbulent kinetic energy for baseline (left) and winglet cases (right)

Grahic Jump Location
Fig. 12

Data extracted from a vertical line at (x′/R)=0.8 from the overall averages of 21 phases (0–120 deg with 6 deg intervals) for (a) axial velocity, (b) out-of-plane vorticity, and (c) turbulent kinetic energy for baseline and winglet cases

Grahic Jump Location
Fig. 13

Vortex center positions from vortex age 30 deg to 330 deg with 30 deg intervals for the baseline and winglet cases

Grahic Jump Location
Fig. 14

(a) Vortex-induced swirl (tangential) velocity magnitude, (b) out-of-plane vorticity, and (c) turbulent kinetic energy distributions along a horizontal line intersecting the center of second vortex core at rotor phase 60 deg (vortex age 180 deg). Horizontal axis is the nondimensional distance from the vortex core center normalized by the tip chord length of the rotor blade.

Grahic Jump Location
Fig. 15

Comparison of vortex core models with current experimental data for three different phases and ages. Vortex ages 60 deg, 180 deg, and 300 deg correspond to phase 60 deg of blades 1–3, respectively, (a) baseline and (b) winglet cases.

Grahic Jump Location
Fig. 16

Vortex core growth for the baseline case from vortex age 12 deg to 348 deg with 6 deg intervals compared to winglet case. The vortex core expansion model of Sant et al. [32] is also presented.

Grahic Jump Location
Fig. 17

Estimated rotor induced drag for baseline and winglet cases, calculated for rotor phases 24–114 deg



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