The aerodynamic characteristics of a NACA0018 aerofoil have been investigated experimentally for incidence angles ranging from to in closed-jet and open-jet wind tunnels with different blockage coefficients at Reynolds numbers from 60,000 to 140,000. The results provide a comprehensive data set for studying the performance of typical, small-scale Darrieus wind turbine blades which mainly operate at relatively low Reynolds number and experience extreme angles of attack, particularly during start-up. Measurements in both very high and very low blockage, open-jet wind tunnels capture a “second-stall” phenomenon at high angles of attack, but this behaviour is not observed in the closed-jet wind tunnel confirming the sensitivity of aerofoil performance at extreme incidence to wind tunnel configuration. Surface flow visualisation suggests that the “second-stall” occurs when the flow separation point near the leading edge of the aerofoil moves from the suction side to the pressure side which leads to a sudden change of wake structure. In the closed-jet wind tunnel, the tunnel walls constrain the wake and prevent the flow from switching from one regime to another. The measured data are also used to demonstrate that established wind tunnel blockage corrections break down under these extreme, post-stall angles of attack.
Kirke BK. Evaluation of self-starting vertical axis wind turbines for stand-alone applications. PhD Thesis, School of Engineering, Griffith University, Australia, 1998.
2.
Pawsey NCK. Development and evaluation of passive variable-pitch vertical axis wind turbines. PhD Thesis, School of Mechanical and Manufacturing Engineering, The University of New South Wales, Australia, 2002.
3.
DominyRGLuntPBickerdykeA. Self-starting capability of a Darrieus turbine. Proc IMechE, Part A: J Power and Energy2007; 221: 111–120.
4.
KentfieldJAC. The fundamentals of wind-driven water pumpers, 1st ed. London: Taylor and Francis, 1996.
5.
RossettiAPavesiG. Comparison of different numerical approaches to the study of the H-Darrieus turbines start-up. J Renew Energy2013; 50: 7–19.
6.
Carmichael BH. Low Reynolds number airfoil survey. USA: NASA CR 165803, Vol. I, 1981.
7.
MuellerTJDeLaurierJD. Aerodynamics of small vehicles. Ann Rev Fluid Mech2003; 35: 89–111.
8.
YarusevychSSullivanPEKawallJG. On vortex shedding from an airfoil in low-Reynolds-number flows. Journal of Fluid Mech2009; 632: 245–271.
9.
SeligMSGuglielmoJJBroerenAP. Summary of low-speed airfoil data1995; vol. 1Virginia Beach, VA: SoarTech Publications.
10.
Worasinchai S, Ingram GL and Dominy RG. The physics of H-Darrieus turbine self-starting capability: flapping-wing perspective In: Proceedings of ASME turbo expo, Copenhagen, Denmark, 11–15 June 2012, Paper No. GT2012-69075, pp.869–878.
11.
Sheldahl RE and Klimas PC. Aerodynamic characteristics of seven symmetrical airfoil sections through 180-degree angle of attack for use in aerodynamic analysis of vertical axis wind turbines. USA: National Renewable Energy Laboratory, SAND80-2114, 1981.
12.
HillNDominyRGIngramG. Darrieus turbines: the physics of self-starting. Proc IMechE, Part A: J Power and Energy2008; 223: 21–29.
13.
McGowan R, Raghav VS and Komerath NM. Optimization of a vertical axis micro wind turbine for low tip speed ratio operation. In: Proceedings of the AIAA IECEC conference, Atlanta, GA, 2012.
14.
WorasinchaiSIngramGLDominyRG. A low-Reynolds-number, high-angle-of-attack investigation of wind turbine aerofoils. Proc IMechE, Part A: J Power and Energy2011; 226: 748–763.
15.
Swalwell KE, Sheridan J and Melbourne WH. The effect of turbulence intensity on stall of the NACA 0021 aerofoil. In: 14th Australasian fluid mechanics conference Adelaide University, Adelaide, Australia, 10–14 December 2001.
16.
AbbottIHVon DoenhoffAE. Theory of wing sections: including a summary of airfoil data, New York: Dover Publications, 1959.
17.
Selig MS and McGranahan BD. Wind tunnel aerodynamic tests of six airfoils for use on small wind turbines. Colorado: National Renewable Energy Laboratory, 2004.
18.
Gerakopulos R, Boutilier MSH and Yarusevych S. Aerodynamic characterization of a NACA 0018 airfoil at low Reynolds numbers. In: Proceedings of the 40th AIAA fluid dynamics conference and exhibit, Chicago, IL, 28 June–1 July 2010, AIAA Paper No. 2010-4629.
19.
Garner HC, Rogers EWE, Acum WEA, et al. Subsonic wind tunnel wall corrections. AGARDograph 109, North Atlantic Treaty Organization (NATO), 1966.
MaederPFWoodAD. Transonic wind tunnel test sections. J Zeitschrift für angewandte Mathematik und Physik ZAMP1956; 7: 177–212.
22.
Sims-Williams DB and Dominy RG. The design of an open-jet wind tunnel for model testing. SAE Technical Paper 2002-01-3340, 2002.
23.
CastelliMREnglaroABeniniE. The Darrieus wind turbine: Proposal for a new performance prediction model based on CFD. J Energy2011; 36: 4919–4934.
24.
Fuglsang P, Antoniou I, Sørensen NN, et al. Validation of a wind tunnel testing facility for blade surface pressure measurements. Denmark: Risø-R-981(EN), Risø National Laboratory, 1998.
25.
DominyRGHodsonHP. An investigation of factors influencing the calibration of 5-hole probes for 3-D flow measurements. ASME J Turbomachine1995; 115: 513–519.
26.
IngramGGregory-SmithD. An automated instrumentation system for flow and loss measurements in a cascade. Flow Measurement Instrument2006; 17: 23–28.
27.
Du L, Berson A and Dominy RG. NACA0018 behaviour at high angles of attack and at Reynolds numbers appropriate for small turbines. Durham University ECS Technical Report ECR-TR 2014/08.
28.
TimmerWA. Two-dimensional low-Reynolds number wind tunnel results for airfoil NACA 0018. Wind Eng2008; 32: 525–537.
29.
Worasinchai S. Small wind turbine starting behaviour. PhD Thesis, School of Engineering and computing science, University of Durham, 2012.
30.
Maskell EC. A theory of the blockage effects on bluff bodies and stalled wings in a closed wind tunnel. ARC RM 3400, 1963.
31.
Mangler W. The lift distribution of wings with end plates. NACA Technical Memorandum No. 856, Washington, 1938.
