David Marten Chair of Fluid Dynamics, Hermann-F € ottinger-Institut, Technische Universit € at Berlin, M€ uller-Breslau-Str. 8, Berlin 10623, Germany e-mail: david.marten@tu-berlin.de Alessandro Bianchini Department of Industrial Engineering, University of Florence, Via di Santa Marta 3, Firenze 50139, Italy e-mail: bianchini@vega.de.unifi.it Georgios Pechlivanoglou Chair of Fluid Dynamics, Hermann-F € ottinger-Institut, Technische Universit € at Berlin, M€ uller-Breslau-Str. 8, Berlin 10623, Germany e-mail: george@pechlivanoglou.com Francesco Balduzzi Department of Industrial Engineering, University of Florence, Via di Santa Marta 3, Firenze 50139, Italy e-mail: balduzzi@vega.de.unifi.it Christian Navid Nayeri Chair of Fluid Dynamics, Hermann-F € ottinger-Institut, Technische Universit € at Berlin, M€ uller-Breslau-Str. 8, Berlin 10623, Germany e-mail: christian.nayeri@tu-berlin.de Giovanni Ferrara Department of Industrial Engineering, University of Florence, Via di Santa Marta 3, Firenze 50139, Italy e-mail: giovanni.ferrara@unifi.it Christian Oliver Paschereit Chair of Fluid Dynamics, Hermann-F € ottinger-Institut, Technische Universit € at Berlin, M€ uller-Breslau-Str. 8, Berlin 10623, Germany e-mail: oliver.paschereit@tu-berlin.de Lorenzo Ferrari CNR-ICCOM, National Research Council of Italy, Via Madonna del Piano 10, Sesto Fiorentino 50019, Italy e-mail: lorenzo.ferrari@iccom.cnr.it Effects of Airfoil’s Polar Data in the Stall Region on the Estimation of Darrieus Wind Turbine Performance Interest in vertical-axis wind turbines (VAWTs) is experiencing a renaissance after most major research projects came to a standstill in the mid 1990s, in favor of conventional horizontal-axis turbines (HAWTs). Nowadays, the inherent advantages of the VAWT con- cept, especially in the Darrieus configuration, may outweigh their disadvantages in spe- cific applications, like the urban context or floating platforms. To enable these concepts further, efficient, accurate, and robust aerodynamic prediction tools and design guide- lines are needed for VAWTs, for which low-order simulation methods have not reached yet a maturity comparable to that of the blade element momentum theory for HAWTs’ applications. The two computationally efficient methods that are presently capable of capturing the unsteady aerodynamics of Darrieus turbines are the double multiple streamtubes (DMS) theory, based on momentum balances, and the lifting line theory (LLT) coupled to a free vortex wake model. Both methods make use of tabulated lift and drag coefficients to compute the blade forces. Since the incidence angles range experi- enced by a VAWT blade is much wider than that of a HAWT blade, the accuracy of polars in describing the stall region and the transition toward the “thin plate like” behavior has a large effect on simulation results. This paper will demonstrate the importance of stall and poststall data handling in the performance estimation of Darrieus VAWTs. Using validated CFD simulations as a baseline, comparisons are provided for a blade in VAWT-like motion based on a DMS and a LLT code employing three sets of poststall data obtained from a wind tunnel campaign, XFoil predictions extrapolated with the Viterna–Corrigan model and a combination of them. The polar extrapolation influence on quasi-steady operating conditions is shown and azimuthal variations of thrust and tor- que are compared for exemplary tip-speed ratios (TSRs). In addition, the major relevance of a proper dynamic stall model into both the simulation methods is highlighted and discussed. [DOI: 10.1115/1.4034326] Introduction Increasing interest is presently being paid by the researchers and industrial manufacturers in rediscovering vertical-axis wind turbines (VAWTs), after most major research projects came to a Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 28, 2016; final manuscript received July 4, 2016; published online September 13, 2016. Editor: David Wisler. Journal of Engineering for Gas Turbines and Power FEBRUARY 2017, Vol. 139 / 022606-1 Copyright V C 2017 by ASME Downloaded from https://asmedigitalcollection.asme.org/gasturbinespower/article-pdf/139/2/022606/6175472/gtp_139_02_022606.pdf by Tu Berlin Universitaetsbibl.im Volkswagen-haus user on 20 December 2019