Numerical study of the effect of surface grooves on the aerodynamic performance of a NACA 4415 airfoil for small wind turbines

Abstract

Indented surface grooves can eliminate the laminar separation bubbles formed on airfoil surfaces, and thus have the potential to improve the aerodynamic performance of small wind turbines. In this study, a three-equation transitional turbulence model was selected and validated with experimental data to simulate the 2D flow around a NACA 4415 airfoil. Parametric simulation of surface groove characteristics was then conducted to investigate their effects on aerodynamic behavior. It was found that the recess depth ratio (h/δ, h: groove recess depth, δ: baseline boundary layer thickness) is the key influencing factor among the groove feature parameters, with the most effective value between h/δ=1.0 and 1.5. A smaller aspect ratio of recess depth to groove width is required to trap the vortex for a shallow recess depth, while a higher aspect ratio can stabilize the vortex for a deep recess. The endpoint of a groove can affect the potential vortex size within it, and the optimum endpoint is located around 0.16c (c: airfoil chord). Moreover, a rectangular groove especially for a recess depth ratio h/δ=1.2−1.5 offers better aerodynamic performance than an arc groove, as the rectangular configuration more efficiently restricts the flow motion inside the groove.