Effect of leading edge spherical tubercles on the aerodynamic performance of a 2D wind turbine airfoil at low reynolds numbers using computational fluid dynamics

The majority of wind power is currently produced on high wind speed sites by large wind turbine, whereas small wind turbines often operate in light wind conditions. Small capacity wind turbines have not received the same engineering attention as their large counterparts. This is partially due to a number of unique problems that small wind turbines experience. The most relevant are: low operating Reynolds number (Re<500,000) and high angles of attack. Several studies have suggested that flow control devices such as the spherical tubercle could be used to increase lift before stall and generate more power in such situations. The aim of this study is to determine the effect of tubercle amplitude on aerodynamic performance of an airfoil at low-Re numbers (Re=300,000 & Re=400,000). Three amplitudes were considered in this study: A1=0.005c, A2=0.01c, and A3=0.03c. A detailed 2D simulation study is carried out using a calibrated Transition SST k-ω turbulence model to obtain aerodynamic coefficients and flow characteristics. Results indicate that small tubercles perform better overall than larger tubercles. The airfoil with the smallest tubercle outperforms the unmodified airfoil at both studied Reynolds numbers at angles of attack 0° – 4°. The analysis of the aerodynamic coefficients indicates that the improvement of the aerodynamic performance of the airfoils with tubercles is due to the reduction of the drag coefficient. Pressure, intermittency and wall shear stress contours suggest that the overall drag reduction is achieved through the decrease of friction drag.