An annotated database of low Reynolds aerodynamic coefficients for the NACA0021 airfoil

Wind industry needs high quality airfoil data (namely lift, drag and moment coefficients) for ranges of the angle of attack (AoA) much wider than those that one can commonly get from the relevant technical literature dealing with aerospace or turbomachinery applications. Accurate aerodynamic coefficients are useful both in case of horizontal-axis wind turbines (HAWTs) in the root region and for vertical-axis ones (VAWTs), where the AoA varies continuously during the revolution, often experiencing stall. This need prompted the research group to establish a long-term research program aimed at assessing high quality polar data for several airfoils (symmetric and cambered) for use in wind energy. As a part of this program, in this study an extended survey of the technical literature has been carried out for the NACA0021 airfoil, often used in wind energy applications, and especially in VAWTs. Analogous to a twin study presented within the same proceeding collection for another symmetric airfoil, experimental and numerical data have been collected, compared and critically discussed. Original simulations and tests from the authors are also provided. The scope of the study is to provide the scientific community with an annotated database of aerodynamic coefficients for the NACA0021 airfoil, making accurate and robust results available to any researcher willing to use this airfoil in wind energy applications.