Wind turbine industry has a special need for accurate post stall airfoil data. While literature often covers incidence ranges [−10 deg, +25 deg], smaller machines experience a range of up to 90 deg for horizontal axis and up to 360 deg for vertical axis wind turbines (VAWTs). The post stall data of airfoils is crucial to improve the prediction of the start-up behavior as well as the performance at low tip speed ratios. The present paper analyzes and discusses the performance of the symmetrical NACA 0021 airfoil at three Reynolds numbers (Re = 100 k, 140 k, and 180 k) through 180 deg incidence. The typical problem of blockage within a wind tunnel was avoided using an open test section. The experiments were conducted in terms of surface pressure distribution over the airfoil for a tripped and a baseline configuration. The pressure was used to gain lift, pressure drag, moment data. Further investigations with positive and negative pitching revealed a second hysteresis loop in the deep post stall region resulting in a difference of 0.2 in moment coefficient and 0.5 in lift.

References

References
1.
Selig
,
M. S.
,
Donovan
,
J.
, and
Fraser
,
D.
,
1989
,
Airfoils at Low Speeds (SoarTech 8)
,
SoarTech Aero Publications
, Virginia Beach, VA.
2.
Selig
,
M. S.
,
Guglielmo
,
J. J.
,
Broeren
,
A. P.
, and
Giguère
,
P.
,
1995
,
Summary of Low-Speed Airfoil Data
, Vol. 1,
SoarTech Publications
, Virginia Beach, VA.
3.
Selig
,
M. S.
,
Lyon
,
C.
,
Giguère
,
P.
,
Ninham
,
C. P.
, and
Guglielmo
,
J. J.
,
1996
,
Summary of Low-Speed Airfoil Data
, Vol.
2
,
SoarTech Publications
, Virginia Beach, VA.
4.
Dominy
,
R.
,
Lunt
,
P.
,
Bickerdyke
,
A.
, and
Dominy
,
J.
,
2007
, “
Self-Starting Capability of a Darrieus Turbine
,”
Proc. Inst. Mech. Eng., Part A
,
221
(
1
), pp.
111
120
.
5.
Worasinchai
,
S.
,
Ingram
,
G. L.
, and
Dominy
,
R. G.
,
2012
, “
Effects of Wind Turbine Starting Capability on Energy Yield
,”
ASME J. Eng. Gas Turbines Power
,
134
(
4
), p.
042603
.
6.
Sheldahl
,
R. E.
, and
Klimas
,
P. C.
,
1981
, “
Aerodynamic Characteristics of Seven Symmetrical Airfoil Sections Through 180-Degree Angle of Attack for Use in Aerodynamic Analysis of Vertical Axis Wind Turbines
,” Sandia National Laboratories, Albuquerque, NM, Technical Report No.
SAND-80-2114
.https://prod.sandia.gov/techlib-noauth/access-control.cgi/1980/802114.pdf
7.
Dossena
,
V.
,
Persico
,
G.
,
Paradiso
,
B.
,
Battisti
,
L.
,
Dell'Anna
,
S.
,
Brighenti
,
A.
, and
Benini
,
E.
,
2015
, “
An Experimental Study of the Aerodynamics and Performance of a Vertical Axis Wind Turbine in a Confined and Unconfined Environment
,”
ASME J. Energy Resour. Technol.
,
137
(
5
), p.
051207
.
8.
Bianchini
,
A.
,
Balduzzi
,
F.
,
Rainbird
,
J. M.
,
Peiro
,
J.
,
Graham
,
J. M. R.
,
Ferrara
,
G.
, and
Ferrari
,
L.
,
2015
, “
An Experimental and Numerical Assessment of Airfoil Polars for Use in Darrieus Wind Turbines—Part II: Post-Stall Data Extrapolation Methods
,”
ASME J. Eng. Gas Turbines Power
,
138
(
3
), p.
032603
.
9.
Worasinchai
,
S.
,
Ingram
,
G. L.
, and
Dominy
,
R. G.
,
2011
, “
A Low-Reynolds-Number, High-Angle-of-Attack Investigation of Wind Turbine Aerofoils
,”
Proc. Inst. Mech. Eng., Part A
,
225
(
6
), pp.
748
763
.
10.
Worasinchai
,
S.
,
2012
, “
Small Wind Turbine Starting Behaviour
,”
Ph.D. thesis
, University of Durham, Durham, UK.http://etheses.dur.ac.uk/4436/
11.
Du
,
L.
,
Berson
,
A.
, and
Dominy
,
R. G.
,
2014
, “
Aerofoil Behaviour at High Angles of Attack and at Reynolds Numbers Appropriate for Small Wind Turbines
,”
Proc. Inst. Mech. Eng., Part C: J. Mech. Eng. Sci.
,
229
(
11
), pp.
2007
2022
.
12.
Du
,
L.
,
Berson
,
A.
, and
Dominy
,
R. G.
,
2014
, “
NACA0018 Behaviour at High Angles of Attack and at Reynolds Numbers Appropriate for Small Wind Turbines
,” Durham University, Durham, UK, Report No. ECS-TR 2014/08.
13.
Rainbird
,
J.
,
2007
, “
The Aerodynamic Development of a Vertical Axis Wind Turbine
,” Master's thesis, University of Durham, Durham, UK.
14.
Rainbird
,
J. M.
,
Peirá
,
J.
, and
Graham
,
J. M. R.
,
2015
, “
Blockage-Tolerant Wind Tunnel Measurements for a NACA 0012 at High Angles of Attack
,”
J. Wind Eng. Ind. Aerodyn.
,
145
, pp.
209
218
.
15.
Holst
,
D.
,
Balduzzi
,
F.
,
Bianchini
,
A.
,
Church
,
B.
,
Wegner
,
F.
,
Pechlivanoglou
,
G.
,
Ferrari
,
L.
,
Ferrara
,
G.
,
Nayeri
,
C. N.
, and
Paschereit
,
C. O.
,
2018
, “
Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and CFD
,”
ASME J. Eng. Gas Turbines Power
(accepted).
16.
Holst
,
D.
,
Church
,
B.
,
Wegner
,
F.
,
Pechlivanoglou
,
G.
,
Nayeri
,
C. N.
, and
Paschereit
,
C. O.
,
2018
, “
Experimental Analysis of a NACA 0021 Airfoil Under Dynamic Angle of Attack Variation and Low Reynolds Numbers
,”
ASME J. Eng. Gas Turbines Power
(accepted).
17.
Stack
,
J.
,
1931
, “
Tests in the Variable Density Wind Tunnel to Investigate the Effects of Scale and Turbulence on Airfoil Characteristics
,” National Advisory Committee for Aeronautics, Washington, DC, Technical Report No. NACA-TN-364.
18.
Jacobs
,
E. N.
,
1932
, “
The Aerodynamic Characteristics of Eight Very Thick Airfoils From Tests in the Variable Density Wind Tunnel
,” National Advisory Committee for Aeronautics. Langley Aeronautical Laboratory, Langley Field, VA, Technical Report No. NACA-TR-391.
You do not currently have access to this content.