This paper presents the wind tunnel experimental results to investigate the effects of surface gradient-of-curvature on aerodynamic performance of a low Reynolds number airfoil Eppler 387 for use in small-scale wind turbines. The prescribed surface curvature distribution blade design method is applied to the airfoil E387 to remove the gradient-of-curvature discontinuities and the redesigned airfoil is denoted as A7. Both airfoils are manufactured with high precision to reflect the design. Low-speed wind tunnel experiments are conducted to both airfoils at chord based Reynolds numbers 100 000, 200 000, and 300 000. Surface pressure measurements are used to calculate the lift and pitching-moment data, and the wake survey method is applied to obtain the drag data. The experimental results of E387 are compared with NASA Low Turbulence Pressure Tunnel (LTPT) results for validation. The gradient-of-curvature discontinuities of E387 result in a larger laminar separation bubble which causes higher drag at lower angles of attack. As the angle of attack increases the separation bubble of the airfoil E387 moves faster towards the leading edge than that of A7, resulting in a premature bubble bursting and earlier stall on E387. The impact of the gradient-of-curvature distribution on the airfoil performance is more profound at higher angles of attack and lower Reynolds number. The aerodynamic improvements are integrated over the 3D geometry of a 3 kW small wind turbine, resulting in up to 10% increase in instantaneous power and 1.6% increase in annual energy production. It is experimentally concluded that an improved curvature distribution results in a better airfoil performance, leading to higher energy output efficiency.

1.
World Wind Energy Association
,
Small Wind World Report No. 2014
, Bonn, Germany, March,
2014
.
2.
T.
Korakianitis
,
M. A.
Rezaienia
,
X.
Shen
,
E. J.
Avital
,
A.
Munjiza
,
P. H.
Wen
, and
J.
Williams
, “
Aerodynamics of wind turbine technology
,” in
Handbook of Clean Energy Systems
(Wiley,
2015
).
3.
T. G.
Wang
,
L.
Wang
,
W.
Zhong
,
B. F.
Xu
, and
L.
Chen
, “
Large-scale wind turbine blade design and aerodynamic analysis
,”
Chin. Sci. Bull.
57
(
5
),
466
472
(
2012
).
4.
Y.
Li
, “
The status of large scale wind turbine technology development
,”
Appl. Math. Mech.
34
(
10
),
1003
1011
(
2013
).
5.
N. D.
Sandham
, “
Transitional separation bubbles and unsteady aspects of aerofoil stall
,”
Aeronaut. J.
112
(
1133
),
395
404
(
2008
).
6.
R. K.
Singh
and
M. R.
Ahmed
, “
Blade design and performance testing of a small wind turbine rotor for low wind speed applications
,”
Renewable Energy
50
,
812
819
(
2013
).
7.
K. W.
Van Treuren
, “
Small-scale wind turbine testing in wind tunnels under low Reynolds number conditions
,”
J. Energy Resour. Technol.
137
(
5
),
051208
(
2015
).
8.
P.
Giguere
and
M. S.
Selig
, “
New airfoils for small horizontal axis wind turbines
,”
J. Sol. Energy Eng.
120
(
2
),
108
114
(
1998
).
9.
K. R.
Ram
,
S.
Lal
, and
M. R.
Ahmed
, “
Low Reynolds number airfoil optimization for wind turbine applications using genetic algorithm
,”
J. Renewable Sustainable Energy
5
(
5
),
052007
(
2013
).
10.
D. M.
Somers
and
M. D.
Maughmer
, “
Theoretical aerodynamic analyses of six airfoils for use on small wind turbines
,”
Technical Report No. NREL/SR-500-33295
, National Renewable Energy Laboratory,
2003
.
11.
J. C. C.
Henriques
,
F.
Marques da Silva
,
A. I.
Estanqueiro
, and
L. M. C.
Gato
, “
Design of a new urban wind turbine airfoil using a pressure-load inverse method
,”
Renewable Energy
34
(
12
),
2728
2734
(
2009
).
12.
M.
Islam
,
M. R.
Amin
,
D. S.-K.
Ting
, and
A.
Fartaj
, “
Selection of airfoils for straight-bladed vertical axis wind turbines based on desirable aerodynamic characteristics
,” in
ASME 2008 International Mechanical Engineering Congress and Exposition
(
American Society of Mechanical Engineers
,
2008
), pp.
3
12
.
13.
M.
Marnett
,
S.
Yang
, and
W.
Schroder
, “
Lightweight airfoil design for a series of small vertical axis wind turbines
,” in
European Wind Energy Conference and Exhibition
(
2010
), Vol.
6
, pp.
4232
4238
.
14.
R. K.
Singh
,
M. R.
Ahmed
,
M. A.
Zullah
, and
Y.-H.
Lee
, “
Design of a low Reynolds number airfoil for small horizontal axis wind turbines
,”
Renewable Energy
42
,
66
76
(
2012
).
15.
R.
Mcghee
,
B.
Walker
, and
B.
Millard
, “
Experimental results for the Eppler 387 airfoil at low Reynolds numbers in the Langley low-turbulence pressure tunnel
,” NASA Technical Memorandum 4062, NASA,
1988
.
16.
M. S.
Selig
,
R. W.
Deters
, and
G. A.
Williamson
, “
Wind tunnel testing airfoils at low Reynolds numbers
,” in
49th AIAA Aerospace Sciences Meeting
(
2011
), pp.
4
7
.
17.
I. A.
Hamakhan
and
T.
Korakianitis
, “
Aerodynamic performance effects of leading-edge geometry in gas-turbine blades
,”
Appl. Energy
87
(
5
),
1591
1601
(
2010
).
18.
K.
Siddappaji
,
M. G.
Turner
, and
A.
Merchant
, “
General capability of parametric 3D blade design tool for turbomachinery
,” in
ASME Turbo Expo 2012: Turbine Technical Conference and Exposition
(American Society of Mechanical Engineers,
2012
), pp.
2331
2344
.
19.
T.
Korakianitis
, “
Design of airfoils and cascades of airfoils
,”
AIAA J.
27
(
4
),
455
461
(
1989
).
20.
A. F.
Nemnem
,
M. G.
Turner
,
K.
Siddappaji
, and
M.
Galbraith
, “
A smooth curvature-defined meanline section option for a general turbomachinery geometry generator
,” in
ASME Turbo Expo 2014: Turbine Technical Conference and Exposition
(American Society of Mechanical Engineers,
2014
), p.
V02BT39A026
.
21.
H. P.
Hodson
, “
Boundary-layer transition and separation near the leading edge of a high-speed turbine blade
,”
J. Eng. Gas Turbines Power
107
(
1
),
127
134
(
1985
).
22.
P.
Stow
, Blading Design for Multi-Stage HP Compressors, Blading Design for Axial Turbomachines,
1989
.
23.
T.
Korakianitis
, “
Prescribed-curvature distribution airfoils for the preliminary geometric design of axial turbomachinery cascades
,”
Trans. ASME J. Turbomach.
115
(
2
),
325
333
(
1993
).
24.
A. P. S.
Wheeler
and
R. J.
Miller
, “
Compressor wake/leading-edge interactions at off design incidences
,” in
ASME Turbo Expo 2008: Power for Land, Sea, and Air
(
American Society of Mechanical Engineers
,
2008
), pp.
1795
1806
.
25.
A. P. S.
Wheeler
,
A.
Sofia
, and
R. J.
Miller
, “
The effect of leading-edge geometry on wake interactions in compressors
,”
J. Turbomach.
131
(
4
),
041013
(
2009
).
26.
A.
Massardo
,
A.
Satta
, and
M.
Marini
, “
Axial flow compressor design optimization: Part II Throughflow analysis
,”
J. Turbomach.
112
(
3
),
405
410
(
1990
).
27.
A. F.
Massardo
and
M.
Scialo
, “
Thermoeconomic analysis of gas turbine based cycles
,”
J. Eng. Gas Turbines Power
122
(
4
),
664
671
(
2000
).
28.
T.
Korakianitis
,
M. A.
Rezaienia
,
I. A.
Hamakhan
,
E. J.
Avital
, and
J. J. R.
Williams
, “
Aerodynamic improvements of wind-turbine airfoil geometries with the prescribed surface curvature distribution blade design (CIRCLE) method
,”
J. Eng. Gas Turbines Power
134
(
8
),
082601
(
2012
).
29.
Y.
Song
,
C. W.
Gu
, and
Y. B.
Xiao
, “
Numerical and theoretical investigations concerning the continuous-surface-curvature effect in compressor blades
,”
Energies
7
(
12
),
8150
8177
(
2014
).
30.
X.
Shen
,
T.
Korakianitis
, and
E. J.
Avital
, “
Numerical investigation of surface curvature effects on aerofoil aerodynamic performance
,”
Appl. Mech. Mater.
798
,
589
595
(
2015
).
31.
T.
Korakianitis
,
M. A.
Rezaienia
,
I. A.
Hamakhan
, and
A. P. S.
Wheeler
, “
Two- and three-dimensional prescribed surface curvature distribution blade design (CIRCLE) method for the design of high efficiency turbines, compressors, and isolated airfoils
,”
J. Turbomach.
135
(
3
),
041002
(
2013
).
32.
A.
Scupi
,
E. J.
Avital
,
D.
Dinu
,
J. J. R.
Williams
, and
A.
Munjiza
, “
Large eddy simulation of flows around a kite used as an auxiliary propulsion system
,”
J. Fluids Eng.
137
(
10
),
101301
(
2015
).
33.
X.
Amandolese
and
E.
Szechenyi
, “
Experimental study of the effect of turbulence on a section model blade oscillating in stall
,”
Wind Energy
7
(
4
),
267
282
(
2004
).
34.
K. E.
Swalwell
,
J.
Sheridan
, and
W. H.
Melbourne
 et al, “
The effect of turbulence intensity on stall of the NACA 0021 aerofoil
,” in
14th Australasian Fluid Mechanics Conference
(
2001
), pp.
10
14
.
35.
K. E.
Swalwell
,
J.
Sheridan
, and
W. H.
Melbourne
, “
The effect of turbulence intensity on performance of a naca4421 airfoil section
,” in
42nd AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada. AIAA
(AIAA,
2004
).
36.
R.
Shelquist
, An introduction to air density and density altitude calculations, Internet Survey,
2012
.
37.
T. W.
Schlatter
and
D. V.
Baker
, “
Algorithms for thermodynamic calculations
,” in
NOAA/ERL PROFS Program Office, Boulder, CO
(
1981
), p.
34
.
38.
J. B.
Barlow
,
A.
Pope
, and
W. H.
Rae
,
Low Speed Wind Tunnel Testing
, 3rd ed. (
Wiley
,
Chichester, New York
),
1999
.
39.
H. P.
Horton
, “
Laminar separation bubbles in two and three dimensional incompressible flow
,” PhD thesis,
Queen Mary College, University of London
,
1968
.
40.
S.-w.
Li
,
S.
Wang
,
J.-p.
Wang
, and
J.-c.
Mi
, “
Effect of turbulence intensity on airfoil flow: Numerical simulations and experimental measurements
,”
Appl. Math. Mech.
32
,
1029
1038
(
2011
).
41.
J.
Stack
, “
Tests in the variable density wind tunnel to investigate the effects of scale and turbulence on airfoil characteristics
,”
Technical Report Technical Note 364
, NACA,
1931
.
42.
J. A.
Hoffmann
, “
Effects of freestream turbulence on the performance characteristics of an airfoil
,”
AIAA J.
29
(
9
),
1353
1354
(
1991
).
43.
M. J.
Churchfield
,
Y.
Li
, and
P. J.
Moriarty
, “
A large-eddy simulation study of wake propagation and power production in an array of tidal-current turbines
,”
Philos. Trans. R. Soc. Lond., A
371
(
1985
),
20120421
(
2013
).
44.
E.
Machefaux
,
G. C.
Larsen
,
N.
Troldborg
,
K.
Hansen
,
N.
Angelou
,
T.
Mikkelsen
,
J.
Mann
 et al, “
Investigation of wake interaction using full-scale lidar measurements and large eddy simulation
,”
Wind Energy
19
(8),
1535
1551
(
2016
).
45.
B.
Hwang
,
T.
Kim
,
S.
Lee
, and
S.
Lee
, “
Aeroacoustic analysis of a wind turbine airfoil and blade on icing state condition
,”
J. Renewable Sustainable Energy
6
(
4
),
042003
(
2014
).
46.
H. Y.
Xu
,
S. L.
Xing
, and
Z. Y.
Ye
, “
Numerical study of the s809 airfoil aerodynamic performance using a co-flow jet active control concept
,”
J. Renewable Sustainable Energy
7
(
2
),
023131
(
2015
).
47.
S.
Sanaye
and
A.
Hassanzadeh
, “
Multi-objective optimization of airfoil shape for efficiency improvement and noise reduction in small wind turbines
,”
J. Renewable Sustainable Energy
6
(
5
),
053105
(
2014
).
48.
R. E.
Wilson
and
P. B. S.
Lissaman
, “
Applied aerodynamics of wind power machines
,”
Technical Report No. PB-238595
, Oregon State University, Corvallis, USA,
1974
.
49.
S. A.
Ning
, AirfoilPrep.py Documentation,
Technical Report No. NREL/TP-5000-58817
, National Renewable Energy Laboratory,
2013
.
50.
L. A.
Viterna
and
D. C.
Janetzke
, “
Theoretical and experimental power from large horizontal-axis wind turbines
,”
Technical Report NASA TM-82944
, National Aeronautics and Space Administration,
1982
.
51.
R. E.
Wilson
, “
Aerodynamic potpourri
,” in
Wind Turbine Dynamics
(
NASA
,
1981
); abstract available at http://adsabs.harvard.edu/abs/1981wtd..nasa....3W.
52.
T.
Burton
,
D.
Sharpe
,
N.
Jenkins
, and
E.
Bossanyi
,
Wind Energy Handbook
(
John Wiley & Sons
,
2001
).
53.
J. V.
Seguro
and
T. W.
Lambert
, “
Modern estimation of the parameters of the Weibull wind speed distribution for wind energy analysis
,”
J. Wind Eng. Ind. Aerodyn.
85
(
1
),
75
84
(
2000
).
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