抄録
In this study, a numerical simulation using a vortex method was performed in order to investigate the aspect of flow and the fluid force around a symmetrical airfoil NACA0012 with relative velocity fluctuation in the direction of flow against main flow velocity. An airfoil with three kinds of fixed attack angle was forced oscillating in ranges of the oscillation amplitude ratio 2a/c=0.5, 1.0, 1.5 and 2.0 and the oscillation frequency ratio f/f_K=0.25, 0.5, 1.0 and 2.0 (here, a :half-amplitude of oscillation, c :chord-length, f :oscillation frequency,f_K :natural Karman vortex shedding frequency from a stationary aerofoil with the attack angle of 90 degrees) at the Reynolds number Re=4.05×10^5 based on the main flow velocity U=20m/s. In results, at the airfoil with attack angle which does not produce the separation on the surface of airfoil in stationary condition, the flow separation was produced even if the movement speed of airfoil does not exceed main flow velocity. At the airfoil with attack angle which can recognize the flow separation clearly in stationary condition, the aspect of flow around airfoil became more complicated without becoming calm. And the variations of fluid forces according to oscillation were obtained in all cases. The relationship between the variation of relative flow velocity and producing the separation including reattachment was investigated in each attack angle. And the separation in stationary condition was observed at smaller attack angle which observed the static stall in the experiment of Maresca et al (1979).
