The Performance of a High-Lift Airfoil in Turbulent Wind

Abstract

The performance of a prospective candidate vertical axis wind turbine airfoil S1223 has been investigated at Reynolds numbers of 55,000, 75,000, and 100,000. The airfoil was tested at angles of attack from −5 to 25 deg in a quasi-isotropic turbulent flow generated using orificed plates. The independent effects of the turbulence intensity were examined with a constant integral length scale Λ/ c=0.14 (where c is the chord length). By increasing the turbulence intensity independently from 4.1 to 9.5%, the airfoil exhibits strong stall characteristics at low turbulence, whereas the stall behaviour becomes less obvious at high turbulence. The independent roles of integral length scale were examined by varying integral length Λ/ c from 0.14 to 0.23. The less turbulent free-stream with smaller length scales appears to delay the stall of the airfoil based on the observation of the lift and drag curve, implying that the smaller integral length under low turbulence intensity (4.1%) delays the boundary layer separation on the suction surface. At a higher turbulence of intensity 9.5%, the effect of varying Λ/ c from 0.08 to 0.15 only leads to subtle changes in the lift and drag.