Research Papers

Vortices' Characteristics to Explain the Flange Height Effects on the Aerodynamic Performances of a Diffuser Augmented Wind Turbine

[+] Author and Article Information
Rym Chaker

Laboratory of Wind Power Control and Energy
Valorization of Waste (LMEEVED),
Research and Technology Center of Energy (CRTEn),
Technopark, BP. 95,
Hammam-Lif 2050, Tunisia
e-mail: rym.chaker@gmail.com

Mouldi Kardous

Laboratory of Wind Power Control and Energy
Valorization of Waste (LMEEVED),
Research and Technology Center of Energy (CRTEn),
Technopark, BP. 95,
Hammam-Lif 2050, Tunisia
e-mail: mouldi.kardous@crten.rnrt.tn

Mahmoud Chouchen

Laboratory of Wind Power Control and Energy
Valorization of Waste (LMEEVED),
Research and Technology Center of Energy (CRTEn),
Technopark, BP. 95,
Hammam-Lif 2050, Tunisia
e-mail: mamadouch2104@gmail.com

Fethi Aloui

Laboratory of Wind Power Control and Energy
Valorization of Waste (LMEEVED),
Research and Technology Center of Energy (CRTEn),
Technopark, BP. 95,
Hammam-Lif 2050, Tunisia
e-mail: aloui_fethi@yahoo.fr

Sassi Ben Nasrallah

Laboratory of Wind Power Control and Energy
Valorization of Waste (LMEEVED),
National Engineering School of Monastir,
Avenue Ibn El Jazzar,
Monastir 5019, Tunisia
e-mail: Sassi.bennasrallah@enim.rnu.tn

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 January 8, 2016; final manuscript received September 29, 2016; published online October 24, 2016. Assoc. Editor: Douglas Cairns.

J. Sol. Energy Eng 138(6), 061013 (Oct 24, 2016) (7 pages) Paper No: SOL-16-1014; doi: 10.1115/1.4034906 History: Received January 08, 2016; Revised September 29, 2016

Flange height is between the geometric features that contribute efficiently to improve the diffuser aerodynamic performances. Results obtained from wind tunnel experiments, particle image velocimetry (PIV) measurements, and numerical simulations reveal that at the diffuser inlet section, the wind velocity increases as the flange height increases. Nevertheless, there is an optimal ratio (flange height/inlet section diameter, Hopt/Da ≈ 0.15) beyond it, the flange height effect on the velocity increase diminishes. This behavior can be explained by both the positions of the two contra-rotating vortices generated downstream of the diffuser and the pressure coefficient at their centers. Indeed, it was found that, as the flange height increases, the two vortices move away from each other in the flow direction and since the flange height exceeds (Hopt/Da), they became too distant from each other and from the flange. While the pressure coefficients at the vortices' centers increase with (H/Da), attain a maximum when (Hopt/Da) is reached, and then decrease. This suggests that the wind velocity increase depends on the pressure coefficient at the vortices' centers. Therefore, it depends on the vortices' locations which are in turn controlled by the flange height. In practice, this means that the diffuser could be more efficient if equipped with a control system able to hold the vortices too near from the flange.

Copyright © 2016 by ASME
Your Session has timed out. Please sign back in to continue.


Ragheb, M. , 2014, “ Wind Energy Converters Concepts,” University of Illinois at Urbana-Champaign, Champaign, IL.
Lilley, G. M. , and Rainbird, W. J. A. , 1956, “ Preliminary Report on the Design and Performance of Ducted Windmills,” College of Aeronautics, Cranfield, UK, CoA Reports, Technical Report No. 102, p. 73.
Oman, R. A. , and Foreman, K. M. , 1973, “ Advantages of the Diffuser Augmented Wind Turbine,” Wind Energy Conversion Systems: Workshop Proceedings, Washington, DC, pp. 103–106.
Igra, O. , 1977, “ Compact Shrouds for Wind Turbines,” Energy Convers., 16(4), pp. 149–157. [CrossRef]
Gilbert, B. L. , Oman, R. A. , and Foreman, K. M. , 1978, “ Fluid Dynamics of Diffuser-Augmented Wind Turbines,” J. Energy, 2(6), pp. 368–374. [CrossRef]
Ohya, Y. , and Karasudani, T. A. , 2010, “ Shrouded Wind Turbine Generating High Output Power With Wind-Lens Technology,” J. Energies, 3(4), pp. 634–649. [CrossRef]
Hansen, M. O. L. , Sorensen, N. N. , and Flay, R. G. J. , 2000, “ Effect of Placing a Diffuser Around a Wind Turbine,” J. Wind Energy, 3(4), pp. 207–213. [CrossRef]
Van Bussel, G. J. W. , 2007, “ The Science of Making More Torque From Wind: Diffuser Experiments and Theory Revisited,” J. Phys.: Conf. Ser., 75, p. 012010.
Abe, K. , and Ohya, Y. , 2004, “ An Investigation of Flow Fields Around Flanged Diffusers Using CFD,” J. Wind Eng. Ind. Aerodyn., 92, pp. 315–330. [CrossRef]
Abe, K. , Nishida, M. , Sakurai, A. , Ohya, Y. , Kihara, H. , Wada, E. , and Sato, K. , 2005, “ Experimental and Numerical Investigations of Flow Fields Behind a Small Wind Turbine With a Flanged Diffuser,” J. Wind Eng. Ind. Aerodyn., 93(12), pp. 951–970. [CrossRef]
Phillips, D. G. , Richards, P. J. , and Flay, R. G. J. , 2002, “ CFD Modelling and the Development of the Diffuser Augmented Wind Turbine,” Wind Struct., 5, pp. 267–276. [CrossRef]
ten Hoopen, P. D. C. , 2009, “ An Experimental and Computational Investigation of a Diffuser Augmented Wind Turbine,” Ph.D. thesis, Faculty of Aerospace Engineering, Delft University of Technology, Delft, Netherlands.
Matsushima, T. , Takagi, S. , and Muroyama, S. , 2006, “ Characteristics of a Highly Efficient Propeller Type Small Wind Turbine With a Diffuser,” Renewable Energy, 31(9), pp. 1343–1354. [CrossRef]
Kardous, M. , Chaker, R. , Aloui, F. , and Ben Nasralah, S. , 2013, “ On the Dependence of an Empty Flanged Diffuser Performance on Flange Height: Numerical Simulations and PIV Visualizations,” Renewable Energy, 56, pp. 123–128. [CrossRef]
Chaker, R. , Kardous, M. , Aloui, F. , and Ben Nasralah, S. , 2014, “ Open Angle Effects on the Aerodynamic Performances of a Flanged Diffuser Augmented Wind Turbine (DAWT),” International Journal Conference on Energy and Electrical Engineering, Vol. 2, p. 6.
García, E. , Pizá, R. , Benavides, X. , Quiles, E. , Correcher, A. , and Morant, F. , 2014, “ Mechanical Augmentation Channel Design for Turbine Current Generators,” Adv. Mech. Eng., 6, p. 650131. [CrossRef]
Kale, A. , Gunjal, Y. R. , Jadhav, S. P. , and Tanksale, A. N. , 2013, “ CFD Analysis for Optimization of Diffuser for a Micro Wind Turbine,” IEEE International Conference on Energy Efficient Technologies for Sustainability, Apr. 10–12, pp. 257–260.
Adeel, A. , Zaidi, M. , and Uddin, N. , 2013, “ Numerical Investigations of Subsonic Flow Through a Convergent-Divergent Duct With Varying Flange Heights at Exit,” International Conference on Energy and Sustainability, NED University of Engineering & Technology, Karachi, Pakistan, pp. 15–19.
Ohya, Y. , Karasudani, T. , Sakurai, A. , Abe, K. , and Inoue, M. , 2008, “ Development of a Shrouded Wind Turbine With a Flanged Diffuser,” J. Wind Eng. Ind. Aerodyn., 96(5), pp. 524–539. [CrossRef]
Mansour, K. , and Meskinkhoda, P. , 2014, “ Computational Analysis of Flow Fields Around Flanged Diffusers,” J. Wind Eng. Ind. Aerodyn., 124, pp. 109–120. [CrossRef]
Robinson, S. K. , 1991, “ Coherent Motions in the Turbulent Boundary Layer,” Annu. Rev. Fluid Mech., 23(1), pp. 601–639. [CrossRef]
Roth, M. , and Peikert, R. , 1998, “ A Higher-Order Method for Finding Vortex Core Lines,” IEEE Visualization, Oct. 18–23, pp. 143–150.
Strawn, R. C. , Kenwright, D. N. , and Ahmad, J. , 1999, “ Computer Visualization of Vortex Wake Systems,” AIAA J., 37(4), pp. 511–512. [CrossRef]
Graftieaux, L. , Michard, M. , and Grosjean, N. , 2001, “ Combining PIV, POD and Vortex Identification Algorithms for the Study of Unsteady Turbulent Swirling Flows,” Meas. Sci. Technol., 12(9), pp. 1422–1429. [CrossRef]
Jiang, M. , Machiraju, R. , and Thompson, D. S. , 2002, “ A Novel Approach to Vortex Core Region Detection,” Joint Eurographics IEEE TCVG Symposium on Visualization, pp. 217–225.
Pope, A. , and Harper, J. J. , 1966, Low Speed Wind Tunnel Testing, Wiley, New York, p. 457.
ASCE, Aerodynamics Committee, 1987, “ Wind Tunnel Model Studies of Buildings and Structures,” ASCE Manuals and Reports on Engineering Practice, American Society of Civil Engineers, New York, No. 67, p. 228.
Mehmood, N. , Liang, Z. , and Khan, J. , 2012, “ CFD Study of NACA 0018 for Diffuser Design of Tidal Current Turbines,” Res. J. Appl. Sci. Eng. Technol., 4(21), pp. 4552–4560.


Grahic Jump Location
Fig. 1

Photographs of the tested diffuser and the different rings used

Grahic Jump Location
Fig. 9

Pressure coefficient (Cp) at vortices' centers versus (H/Da)

Grahic Jump Location
Fig. 5

Examples of streamlines for some flange height (PIV measurement): (a) H/Da = 0.05, (b) H/Da = 0.2, and (c) H/Da = 0.3

Grahic Jump Location
Fig. 6

Wind velocity vectors downstream the diffuser (PIV Data)

Grahic Jump Location
Fig. 7

Streamlines, Γ2 criterion, and vortex center positions (experimental data)

Grahic Jump Location
Fig. 8

Motion diagram of the two vortices (represented by the spatial coordinate of their centers Cx and Cy): squares and triangles correspond, respectively, to the first vortex and the second vortex; filled symbol corresponds to the optimal flange height

Grahic Jump Location
Fig. 2

(u/U) versus (H/Da): square point: measured data and circle point: corrected data

Grahic Jump Location
Fig. 3

(u/U) versus (H/Da) for different data sets: filled points correspond to optimal value

Grahic Jump Location
Fig. 4

(u/U) calculated versus (u/U) measured for the whole data sets (H/Da ≤ 0.15)

Grahic Jump Location
Fig. 10

ΔCp and u/U versus H/Da



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