Low Reynolds airfoil family for small horizontal axis wind turbines based on RG15 airfoil

Abstract

The present study introduces a low Reynolds number (Re) airfoil family for the entire blade span of small wind turbines, aiming to reduce the effects related to laminar separation, improve startup response and meet acceptable levels of structural integrity. Six airfoils of varying relative thickness were designed by increasing the thickness distribution of RG15 airfoil up to 50% and adopting a rounded trailing edge with a diameter equal to 1% of the chord length. The aerodynamic performance of RG15 family was initially evaluated by means of XFOIL code at several low Reynolds numbers ranging from 60,000 to 300,000 and angles of attack between − 6° and 14°. XFOIL analysis revealed that increasing relative thickness leads to the reduction of maximum lift-to-drag ratio $$(C_{L} /C_{D} )$$ . However, this percentage reduction decreases with increasing Re. The maximum reduction in maximum $$C_{L} /C_{D}$$ was found at 60,000 Re for the thickest airfoil of RG15 family. Conversely, a growth of maximum lift coefficient $$(C_{L} )$$ was observed by increasing relative thickness. Besides, a Reynolds-Averaged Navier–Stokes (RANS) analysis was also conducted at 300,000 Re to get additional information on the flow characteristics. Comparisons between the XFOIL and RANS data were performed. The results of RANS simulations were generally in accordance with those of XFOIL. However, notable over-estimations of drag coefficient $$(C_{D} )$$ were detected. The behavior of the recirculation area behind the rounded trailing edge and that of the separation bubble near the leading edge for different values of relative thickness and angle of attack was examined. Thickening of the airfoils was found to have a beneficial impact on the appearance of separation bubbles, while no significant effect of the rounded trailing edge on $$C_{L}$$ and $$C_{D}$$ was observed.