Peak lift-to-drag ratio enhancement of the DU12W262 airfoil by passive flow control and its impact on horizontal and vertical axis wind turbines

Recent studies have revealed that passive leading-edge slots on the pressure side has the potential to increase both the peak and overall C-L/C-D of airfoils and may possess an advantage over active methods. This work pursues application of such novel slots to the modern DU12W262 airfoil with a flexible slotshape parametrization coupled with an optimizer to allow other slot concepts as well (suction side and trailing edge slots). Experimentally validated Computational Fluid Dynamics (CFD) simulations are employed for this purpose. It is shown that 16% peak C-L/C-D improvement and overall alpha-C-L/C-D rise are observed without any penalty in stall range. Implications of these are demonstrated on Horizontal- and Vertical-Axis Wind Turbines (HAWT and VAWT) by CFD. It is shown that, HAWT peak C-p of increases by 3.2%. Alternative BEM simulations predict this as high as 7.5%. For the VAWT, the peak C-p remains unchanged, however high tip-speed-ratio (lambda > 3, low wind speed) C-p increases between 3.5 and 9.6% throughout the operational range. This may directly reflect into VAWT urban operation. In summary, the concept is highly successful in improving peak and overall C-L/C-D of a modern airfoil, and this yields to significant enhancements in both HAWTs and VAWTs. (C) 2020 Elsevier Ltd. All rights reserved.