Vortex Scale of Unsteady Separation on a Pitching Airfoil

: The streaklines of unsteady separation on two kinds of pitching airfoils, the NACA65‐0910 and a blunt trailing edge airfoil, were studied by dye flow visualization and by the Schlieren method. The latter visualized the discrete vortices shed from the leading edge. The results of these visualization studies allow a comparison between the dynamic behavior of the streakline of unsteady separation and that of the discrete vortices shed from the leading edge. The influence of the airfoil configuration on the flow characteristics was also examined. Furthermore, the scale of a discrete vortex forming the recirculation region was investigated. The non‐dimensional pitching rate was k= 0.377, the angle of attack αm= 16° and the pitching amplitude was fixed to A=±6° for Re= 4.0 × 103 in this experiment.