EFFECTS OF FREESTREAM TURBULENCE ON THE PERFORMANCE-CHARACTERISTICS OF AN AIRFOIL

THE lift and drag characteristics and associated flowfields over the suction surface of an NACA 0015 airfoil with an aspect ratio of 2.9 were obtained at a Reynolds number of 250,000 for conditions both with and without freestream turbulence (FST). Increasing the FST from 0.25 to 9% resulted in an increase in peak lift coefficient of 30% with no measurable change in the slope of the lift coefficient C(L) vs the curve of the angle of attack alpha; no significant change in drag coefficient C(D) at each alpha occurred. Oil flow visualization results showed an elimination of the laminar separation bubble with FST, corresponding to a disappearance of the hysteresis loop in the performance data; a significant delay in separation was also shown for the case with FST, corresponding to the increase in peak lift coefficient. The results present engineers with information for the design of a wide variety of systems where airfoils experience FST.